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- Front Matter: Volume 10329
- Interometric Techniques I
- World of Photonics Congress-wide Plenary Session
- Interometric Techniques II
- Digital Holography and Holographic Microscopy
- OCT and Coherence Scanning
- High-Speed Techniques
- Fringe Projection I
- Fringe Projection II
- Special Session: Spectroscopic Techniques in Industrial and Astronomical Applications
- High-Resolution Profiling I
- High-Resolution Profiling II
- Joint Session I: High-Precision Measurement of Optical Components and Systems
- Joint Session II: High-Precision Measurement of Optical Components and Systems
- Speckle Metrology
- In-situ and Nondestructive Testing I
- In-situ and Nondestructive Testing II
- In-situ and Nondestructive Testing III
- Posters--Tuesday
Front Matter: Volume 10329
Front Matter: Volume 10329
Show abstract
This PDF file contains the front matter associated with SPIE Proceedings Volume 10329 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.
Interometric Techniques I
Polarization and phase shifting interferometry
Show abstract
This publication presents a novel interferometric method for the simultaneous measurement of the phase and
state of polarization of a light wave with arbitrary, in particular locally varying elliptical polarization. The mea-
surement strategy is based on variations of the reference wave concerning phase and polarization and processing
the interference patterns so obtained. With this method, that is very similar to the classical phase shifting
interferometry, a complete analysis of spatially variant states of polarization and their phase fronts can be done
in one measurement cycle. Furthermore, a direct analysis of specimens under test regarding birefringence and
the impact on the phase of the incoming light can be realized. The theoretical description of the investigated
methods and their experimental implementation are presented.
Increasing the accuracy of tilted-wave-interferometry by elimination of systematic errors
Show abstract
This work investigates methods to eliminate calibration errors as one of the limiting factors to reduce measurement
uncertainty in Tilted-Wave-Interferometry. The correlations between errors in the model parameters and
in the measurement result are investigated, taking into account the symmetry of the surface under test. Two
schemes for the elimination of such errors are introduced: Rotations around the z-axis allow the removal on
non-rotationally symmetric error components. Measurements in lateral shears allow the elimination of calibration
errors with higher spatial frequency. The corresponding algorithms and underlying models are explained
for both approaches and examples for their application are presented.
Full-field heterodyne dynamic interferometry based on hertz-level low differential-frequency acousto-optic frequency shifter
Show abstract
High precision measurement of optical elements with long focal length is affected by vibration, airflow and other
environmental factors due to the long cavity length, which has been difficulty and hot issue in optical machining and
detection. In order to overcome the difficulties of high precision measurement of optical elements with long focal length,
the paper proposes a full-field heterodyne interferometric measurement technique that could effectively suppress the
environmental interference. In the early related research, a series of Hertz-level high-stability, low-differential frequency
acousto-optic frequency shifters were successfully developed, which could be applied to heterodyne interferometry,
instead of traditional phase-shifting intererometry. On this basis, a full-field heterodyne interference measurement system
is developed, using array detector with conventional frame rate for full-field detection, to solve the problem of different
optical paths of reference light and measuring light in dynamic interferometers. It could effectively suppress the vibration,
noise, airflow and other factors, and thus significantly improve measurement accuracy and environmental adaptability. In
typical environment with vibration and airflow, our measurement system can achieve technical indicators as follows:
surface measurement accuracy is better than λ/1000 and repeated measurement accuracy is better than 5λ/10000.
Thereby the new full-field heterodyne interferometry could be applied to dynamic measurement of large-diameter optical
components and systems quality inspection, system installation correction, on-line measurement and other areas.
World of Photonics Congress-wide Plenary Session
Putting a spin on photons
Show abstract
We demonstrate the voltage induced switching of single defect centers between its charge states. The individual charge
states do show different emission wavelengths and are identified by their ground state spin properties.
Interometric Techniques II
Phase imaging using a single-pixel camera
Show abstract
We demonstrate a phase imaging method based on a single-pixel camera based on a complex-amplitude representation to
measure a surface profile of objects. The use of the complex-amplitude representation of the input signal and the phaseshifting
technique enables us to perform the phase imaging of an object, that is, the profilometry. The complex-amplitude
mask can directly represent the Hadamard patterns that have the positive and negative values. The complex-amplitude
masks are displayed on phase modulation mode liquid crystal on silicon spatial light modulator (LCOS-SLM).
Furthermore, the residual area is used for the reference beam with the phase shifting. Therefore, the phase imaging
system with the coaxial structure has high stability for external disturbances.
Spatial-temporal phase shifting interferometry: suppressing phase errors in dynamic Fizeau interferometer
Show abstract
A spatial-temporal phase shifting interferometry is proposed to suppress the phase errors in dynamic Fizeau
interferometer. The process of phase errors suppression in this interferometry includes three steps: (1) utilizing the
spatial phase shifting interferometry to calculate the initial phase; (2) viewing all the effects of the error sources as a
complex; (3) utilizing the temporal phase shifting interferometry to obtain multiple different initial phases and calculate
the average phase. Experimentally, the phase errors are suppressed effectively and the measurement results are in good
agreement with those obtained by Zygo GPI interferometer, which verifies that the proposed interferometry is a powerful
tool for phase errors suppression in dynamic interferometer.
Study on measurement accuracy of active optics null test systems based on liquid crystal spatial light modulator and laser interferometer
Show abstract
A common way to test high-quality aspherical lenses is to use a measurement system based on a set of null corrector and
a laser interferometer. The null corrector can either be a combination of spherical lenses or be a computer generated
hologram (CGH), which compensates the aspheric wave-front being tested. However, the null optics can’t be repeatedly
used once the shape of tested optics changes. Alternative active null correctors have been proposed based on dynamic
phase modulator devices. A typical dynamic phase modulator is liquid crystal spatial light modulator (LCSLM), which
can spatially change the refractive index of the liquid crystal and thus modify the phase of the input wave-front. Even
though the measurement method based on LCSLM and laser interferometer has been proposed and demonstrated for
optical testing several years ago, it still can’t be used in the high quality measurement process due to its limited accuracy.
In this paper, we systematically study the factors such as LCSLM structure parameters, encoding error and laser
interferometer performance, which significantly affect the measurement accuracy. Some solutions will be proposed in
order to improve the measurement accuracy based on LCSLM and laser interferometer.
Digital Holography and Holographic Microscopy
Evaluation of refocus criteria for holographic particle imaging
Show abstract
This paper proposes a quality assessment of focusing criteria for imaging in digital off-axis holography. In literature,
several refocus criteria have been proposed in the past to get the best refocus distance in digital holography. As a general
rule, the best focusing plane is determined by the reconstruction distance for which the criterion function presents a
maximum or a minimum. To evaluate the robustness of these criteria, a set of thirteen criteria is compared with
application on both amplitude and phase images from off-axis holographic data. Experimental results lead to define
general rule and to exhibit the most robust criteria for accurate and rapid refocusing in digital holography.
Topography measurements of high NA aspherical microlenses by digital holographic microscopy with spherical illumination
Show abstract
In this contribution, we propose a method of digital holographic microscopy (DHM) that enables measurement of high
numerical aperture spherical and aspherical microstructures of both concave and convex shapes. The proposed method
utilizes reflection of the spherical illumination beam from the object surface and the interference with a spherical
reference beam of the similar curvature. In this case, the NA of DHM is fully utilized for illumination and imaging of the
reflected object beam. Thus, the system allows capturing the phase coming from larger areas of the quasi-spherical
object and, therefore, offers possibility of high accuracy characterization of its surface even in the areas of high
inclination. The proposed measurement procedure allows determining all parameters required for the accurate shape
recovery: the location of the object focus point and the positions of the illumination and reference point sources. The
utility of the method is demonstrated with characterization of surface of high NA focusing objects. The accuracy is
firstly verified by characterization of a known reference sphere with low error of sphericity. Then, the method is applied
for shape measurement of spherical and aspheric microlenses. The results provide a full-field reconstruction of high NA
topography with resolution in the nanometer range. The surface sphericity is evaluated by the deviation from the best
fitted sphere or asphere, and the important parameters of the measured microlens: e.g.: radius of curvature and conic
constant.
Digital holography on moving objects: multiwavelength height measurements on inclined surfaces
Show abstract
Multiwavelength digital holography on moving objects enables fast and precise inline-measurements of surface pro files. Due to the use of multiple wavelengths, optically rough surfaces with structure heights in the micrometer range can be mapped unambiguously. In this work we explore the influence of the object velocity on height measurements on inclined surfaces. We show measurements using spatial-phase-shifting holography employing two wavelengths and object velocities of up to 90 mm/s with eye-safe cw-lasers with less than 1 mW of laser light. Despite motion blur exceeding the mean speckle size, reliable height measurements can be conducted at these velocities. The height map of a metal cone with two different slope angles (1° , 10° ) is measured at an exposure time of 2 ms. Using line shaped illumination, each frame yields a height map of approximately 2 x 17 mm2. The overlap between the frames allows averaging as the image is put together, improving data quality. The mean repeatability of the height information in the investigated setup is better than 4.5 µm at a synthetic wavelength of 214 µm.
A method for total noise removal in digital holography based on enhanced grouping and sparsity enhancement filtering
Show abstract
In digital holography (DH), the coherent nature of the employed light sources severely degrades the holographic
reconstructions due to a mixture of speckle and incoherent additive noise. These can affect both the visual quality in
holographic imaging and display, and the accuracy of quantitative phase-contrast reconstructions. Typically, the noise
problem is tackled by reducing the illumination coherence, thus the most intuitive way involves the recording of multiple
uncorrelated holograms to be incoherently combined. This framework is known as Multi-Look DH (MLDH). However,
single shot recordings are highly desirable in DH, and numerical methods are required to go beyond the improvement
bound of ML techniques. Among the existing image processing methods, the 3D Block Matching filtering (BM3D) has
shown the best performance. Here we present the MLDH-BM3D, a method specifically suitable to filter DH images that
combines the two aforementioned strategies to overcome their respective limitations. We demonstrate the effectiveness
of this framework in three different experimental situations, i.e. reconstructions of single wavelength holograms and
color holograms in the visible region and the challenging case of the Infrared Radiation Digital Holography (IRDH)
reconstructions, where a very severe noise degradation occurs.
Miniaturized multiwavelength digital holography sensor for extensive in-machine tool measurement
Show abstract
In this paper we present a miniaturized digital holographic sensor (HoloCut) for operation inside a machine tool.
With state-of-the-art 3D measurement systems, short-range structures such as tool marks cannot be resolved inside a machine tool chamber. Up to now, measurements had to be conducted outside the machine tool and thus processing data are generated offline.
The sensor presented here uses digital multiwavelength holography to get 3D-shape-information of the machined sample. By using three wavelengths, we get a large artificial wavelength with a large unambiguous measurement range of 0.5mm and achieve micron repeatability even in the presence of laser speckles on rough surfaces. In addition, a digital refocusing algorithm based on phase noise is implemented to extend the measurement range beyond the limits of the artificial wavelength and geometrical depth-of-focus. With complex wave field propagation, the focus plane can be shifted after the camera images have been taken and a sharp image with extended depth of focus is constructed consequently.
With 20mm x 20mm field of view the sensor enables measurement of both macro- and micro-structure (such as tool marks) with an axial resolution of 1 µm, lateral resolution of 7 µm and consequently allows processing data to be generated online which in turn qualifies it as a machine tool control.
To make HoloCut compact enough for operation inside a machining center, the beams are arranged in two planes: The beams are split into reference beam and object beam in the bottom plane and combined onto the camera in the top plane later on. Using a mechanical standard interface according to DIN 69893 and having a very compact size of 235mm x 140mm x 215mm (WxHxD) and a weight of 7.5 kg, HoloCut can be easily integrated into different machine tools and extends no more in height than a typical processing tool.
With state-of-the-art 3D measurement systems, short-range structures such as tool marks cannot be resolved inside a machine tool chamber. Up to now, measurements had to be conducted outside the machine tool and thus processing data are generated offline.
The sensor presented here uses digital multiwavelength holography to get 3D-shape-information of the machined sample. By using three wavelengths, we get a large artificial wavelength with a large unambiguous measurement range of 0.5mm and achieve micron repeatability even in the presence of laser speckles on rough surfaces. In addition, a digital refocusing algorithm based on phase noise is implemented to extend the measurement range beyond the limits of the artificial wavelength and geometrical depth-of-focus. With complex wave field propagation, the focus plane can be shifted after the camera images have been taken and a sharp image with extended depth of focus is constructed consequently.
With 20mm x 20mm field of view the sensor enables measurement of both macro- and micro-structure (such as tool marks) with an axial resolution of 1 µm, lateral resolution of 7 µm and consequently allows processing data to be generated online which in turn qualifies it as a machine tool control.
To make HoloCut compact enough for operation inside a machining center, the beams are arranged in two planes: The beams are split into reference beam and object beam in the bottom plane and combined onto the camera in the top plane later on. Using a mechanical standard interface according to DIN 69893 and having a very compact size of 235mm x 140mm x 215mm (WxHxD) and a weight of 7.5 kg, HoloCut can be easily integrated into different machine tools and extends no more in height than a typical processing tool.
High-throughput single-shot hyperspectral interferometer for areal profilometry based on microlens array integral field unit
Show abstract
A single-shot technique to measure areal profiles on optically smooth and rough surfaces and for applications in noncooperative
environments is presented. It is based on hyperspectral interferometry (HSI), a technique in which the output
of a white-light interferometer provides the input to a hyperspectral imaging system. Previous HSI implementations
suffered from inefficient utilisation of the available pixels which limited the number of measured coordinates and/or
unambiguous depth range. In this paper a >20-fold increase in pixel utilization is achieved through the use of a 2-D
microlens array as proposed for integral field units in astronomy applications. This leads to a 35×35 channel system with
an unambiguous depth range of 0.88 mm.
OCT and Coherence Scanning
Tomographical process monitoring of laser transmission welding with OCT
Philippe Ackermann,
Robert Schmitt
Show abstract
Process control of laser processes still encounters many obstacles. Although these processes are stable, a narrow process
parameter window during the process or process deviations have led to an increase on the requirements for the process
itself and on monitoring devices.
Laser transmission welding as a contactless and locally limited joining technique is well-established in a variety of demanding production areas. For example, sensitive parts demand a particle-free joining technique which does not affect the inner components.
Inline integrated non-destructive optical measurement systems capable of providing non-invasive tomographical images of the transparent material, the weld seam and its surrounding areas with micron resolution would improve the overall process. Obtained measurement data enable qualitative feedback into the system to adapt parameters for a more robust process.
Within this paper we present the inline monitoring device based on Fourier-domain optical coherence tomography developed within the European-funded research project “Manunet Weldable”. This device, after adaptation to the laser transmission welding process is optically and mechanically integrated into the existing laser system. The main target lies within the inline process control destined to extract tomographical geometrical measurement data from the weld seam forming process. Usage of this technology makes offline destructive testing of produced parts obsolete. 1,2,3,4
Laser transmission welding as a contactless and locally limited joining technique is well-established in a variety of demanding production areas. For example, sensitive parts demand a particle-free joining technique which does not affect the inner components.
Inline integrated non-destructive optical measurement systems capable of providing non-invasive tomographical images of the transparent material, the weld seam and its surrounding areas with micron resolution would improve the overall process. Obtained measurement data enable qualitative feedback into the system to adapt parameters for a more robust process.
Within this paper we present the inline monitoring device based on Fourier-domain optical coherence tomography developed within the European-funded research project “Manunet Weldable”. This device, after adaptation to the laser transmission welding process is optically and mechanically integrated into the existing laser system. The main target lies within the inline process control destined to extract tomographical geometrical measurement data from the weld seam forming process. Usage of this technology makes offline destructive testing of produced parts obsolete. 1,2,3,4
Non-destructive testing of layer-to-layer fusion of a 3D print using ultrahigh resolution optical coherence tomography
Show abstract
Within the last decade, 3D printing has moved from a costly approach of building mechanical items to the
present state-of-the-art phase where access to 3D printers is now common, both in industry and in private places.
The plastic printers are the most common type of 3D printers providing prints that are light, robust and of lower
cost.
The robustness of the structure printed is only maintained if each layer printed is properly fused to its previously printed layers. In situations where the printed component has to accomplish a key mechanical role there is a need to characterize its mechanical strength. This may only be revealed by in-depth testing in order to discover unwanted air-gaps in the structure.
Optical coherence tomography (OCT) is an in-depth imaging method, that is sensitive to variations in the refractive index and therefore can resolve with high resolution translucid samples.
We report on volume imaging of a 3D printed block made with 100% PLA fill. By employing ultrahigh resolution OCT (UHR-OCT) we show that some parts of the PLA volume reveal highly scattering interfaces which likely correspond to transitions from one layer to another. In doing so, we document that UHR-OCT can act as a powerful tool that can be used in detecting fractures between layers stemming from insufficient fusion between printed structure layers. UHR-OCT can therefore serve as an useful assessment method of quality of 3D prints.
The robustness of the structure printed is only maintained if each layer printed is properly fused to its previously printed layers. In situations where the printed component has to accomplish a key mechanical role there is a need to characterize its mechanical strength. This may only be revealed by in-depth testing in order to discover unwanted air-gaps in the structure.
Optical coherence tomography (OCT) is an in-depth imaging method, that is sensitive to variations in the refractive index and therefore can resolve with high resolution translucid samples.
We report on volume imaging of a 3D printed block made with 100% PLA fill. By employing ultrahigh resolution OCT (UHR-OCT) we show that some parts of the PLA volume reveal highly scattering interfaces which likely correspond to transitions from one layer to another. In doing so, we document that UHR-OCT can act as a powerful tool that can be used in detecting fractures between layers stemming from insufficient fusion between printed structure layers. UHR-OCT can therefore serve as an useful assessment method of quality of 3D prints.
Applications of optical coherence tomography in the non-contact assessment of automotive paints
Show abstract
The multiple layer paint systems on modern cars serve two end purposes, they firstly protect against corrosion and
secondly give the desired visual appearance. To ensure consistent corrosion protection and appearance, suitable Quality
Assurance (QA) measures on the final product are required. Various (layer thickness and consistency, layer composition,
flake statistics, surface profile and layer dryness) parameters are of importance, each with specific techniques that can
measure one or some of them but no technique that can measure all or most of them. Optical Coherence Tomography
(OCT) is a 3D imaging technique with micrometre resolution. Since 2016, OCT measurements of layer thickness and
consistency, layer composition fingerprint and flake statistics have been reported. In this paper we demonstrate two more
novel applications of OCT to automotive paints. Firstly, we use OCT to quantify unwanted surface texture, which leads
to an “orange peel” visual defect. This was done by measuring the surface profiles of automotive paints, with an unoptimised
precision of 37 nm over lateral range of 7 mm, to quantify texture of less than 500 nm. Secondly, we
demonstrate that OCT can measure how dry a coating layer is by measuring how fast it is still shrinking quasiinstantaneously,
using Fourier phase sensitivity.
Single-shot multilayer measurement by chromatic confocal coherence tomography
Show abstract
We propose Chromatic Confocal Coherence Tomography as a new system able to achieve corrected topography
measurements of multi-layered specimens by measuring position, thickness and refractive index of each layer
simultaneously at each measurement point. This feature is achieved by a combination of a chromatic confocal
scheme and an interferometric one. The numerical aperture of the used microscope objective has a significant
effect on the measurement uncertainty. Hence, its contribution to uncertainty is discussed in more detail.
Tolerance on sphere radius for the calibration of the transfer function of coherence scanning interferometry
Show abstract
Although coherence scanning interferometry (CSI) commonly achieves a sub-nanometre noise level in surface
topography measurement, the absolute accuracy is difficult to determine when measuring a surface that contains varying
local slope angles and curvatures. Recent research has shown that it is possible to use a single sphere with a radius much
greater than the source wavelength to calibrate the three-dimensional transfer function of a CSI system. A major
requirement is the accurate knowledge of the sphere radius, but the three-dimensional measurement of a sphere with
nanometre level uncertainty is a highly challenging metrology problem, and is not currently feasible. Perfect spheres do
not exist and every measurement has uncertainty. Without having a quantitative understanding of the tolerance of the
sphere radius, the calibration method cannot be used confidently for calibration of the transfer function of a CSI system
that may be used in research laboratories or industry. In this paper, the effects of the tolerance of the radius of the
calibration sphere on surface topography measurements are quantitatively analysed through a computational approach.
CSI measurements of spherical, sinusoidal and rough surfaces are investigated in the presence of various degrees of
radius error. A lookup table that relates the surface height error as a function of the radius error and surface slope angle is
provided. The users may estimate the required tolerances of the sphere radius for their specific surface measurements if
this calibration approach is used. The output of this paper provides a feasibility analysis for this calibration method for
further development and applications.
High-Speed Techniques
GOBO projection for underwater 3D measurement technique
Show abstract
This paper gives an approach for the application of the principle of GOBO projection for underwater 3D measurement
systems based on optical 3D scanners using stereo cameras. The GOBO projection principle is explained and the special
challenges of underwater structured light projection using GOBO projection are discussed.
The new principle was realized in a laboratory setup where camera and projection unit were placed outside a water tank.
Several experiments were performed in order to estimate the necessary measurement conditions and parameters such as
exposure time, camera lens apertures, measurement field size, and object distance. Additionally, selected different fringe
patterns were applied and analyzed. First measurements were performed using a mobile 3D scanner and a GOBO
projection unit.
Verification of real sensor motion for a high-dynamic 3D measurement inspection system
Show abstract
Inline three-dimensional measurements are a growing part of optical inspection. Considering increasing production capacities and economic aspects, dynamic measurements under motion are inescapable. Using a sequence of different pattern, like it is generally done in fringe projection systems, relative movements of the measurement object with respect to the 3d sensor between the images of one pattern sequence have to be compensated.
Based on the application of fully automated optical inspection of circuit boards at an assembly line, the knowledge of the relative speed of movement between the measurement object and the 3d sensor system should be used inside the algorithms of motion compensation. Optimally, this relative speed is constant over the whole measurement process and consists of only one motion direction to avoid sensor vibrations. The quantified evaluation of this two assumptions and the error impact on the 3d accuracy are content of the research project described by this paper.
For our experiments we use a glass etalon with non-transparent circles and transmitted light. Focused on the circle borders, this is one of the most reliable methods to determine subpixel positions using a couple of searching rays. The intersection point of all rays characterize the center of each circle. Based on these circle centers determined with a precision of approximately 1=50 pixel, the motion vector between two images could be calculated and compared with the input motion vector. Overall, the results are used to optimize the weight distribution of the 3d sensor head and reduce non-uniformly vibrations. Finally, there exists a dynamic 3d measurement system with an error of motion vectors about 4 micrometer. Based on this outcome, simulations result in a 3d standard deviation at planar object regions of 6 micrometers. The same system yields a 3d standard deviation of 9 µm without the optimization of weight distribution.
Based on the application of fully automated optical inspection of circuit boards at an assembly line, the knowledge of the relative speed of movement between the measurement object and the 3d sensor system should be used inside the algorithms of motion compensation. Optimally, this relative speed is constant over the whole measurement process and consists of only one motion direction to avoid sensor vibrations. The quantified evaluation of this two assumptions and the error impact on the 3d accuracy are content of the research project described by this paper.
For our experiments we use a glass etalon with non-transparent circles and transmitted light. Focused on the circle borders, this is one of the most reliable methods to determine subpixel positions using a couple of searching rays. The intersection point of all rays characterize the center of each circle. Based on these circle centers determined with a precision of approximately 1=50 pixel, the motion vector between two images could be calculated and compared with the input motion vector. Overall, the results are used to optimize the weight distribution of the 3d sensor head and reduce non-uniformly vibrations. Finally, there exists a dynamic 3d measurement system with an error of motion vectors about 4 micrometer. Based on this outcome, simulations result in a 3d standard deviation at planar object regions of 6 micrometers. The same system yields a 3d standard deviation of 9 µm without the optimization of weight distribution.
High speed imaging for assessment of impact damage in natural fibre biocomposites
Karthik Ram Ramakrishnan,
Stephane Corn,
Nicolas Le Moigne,
et al.
Show abstract
The use of Digital Image Correlation has been generally limited to the estimation of mechanical properties and fracture
behaviour at low to moderate strain rates. High speed cameras dedicated to ballistic testing are often used to measure the
initial and residual velocities of the projectile but rarely for damage assessment. The evaluation of impact damage is
frequently achieved post-impact using visual inspection, ultrasonic C-scan or other NDI methods. Ultra-high speed
cameras and developments in image processing have made possible the measurement of surface deformations and
stresses in real time during dynamic cracking. In this paper, a method is presented to correlate the force- displacement
data from the sensors to the slow motion tracking of the transient failure cracks using real-time high speed imaging.
Natural fibre reinforced composites made of flax fibres and polypropylene matrix was chosen for the study. The creation
of macro-cracks during the impact results in the loss of stiffness and a corresponding drop in the force history. However,
optical instrumentation shows that the initiation of damage is not always evident and so the assessment of damage
requires the use of a local approach. Digital Image Correlation is used to study the strain history of the composite and to
identify the initiation and progression of damage. The effect of fly-speckled texture on strain measurement by image
correlation is also studied. The developed method can be used for the evaluation of impact damage for different
composite materials.
Fringe Projection I
Miniaturization of an optical 3D sensor by additive manufacture of metallic mirrors
Andre Sigel,
Markus Merkel,
Andreas Heinrich
Show abstract
Based on progress in the field of additive manufacturing optical components can now be printed with rapid prototyping
technologies. In this contribution the possibilities of rapid prototyping for optical metrology are exemplified by the
fabrication of miniaturized reflectors and the construction of a miniaturized metrology system designed for an industrial
metrology application.
Focusing on the manufacturing and post processing steps the process chain to fabricate the miniaturized mirror is described. This includes an evaluation of the mirror based on roughness measurements. The reflectors are later utilized in a miniaturized sensor system to scan the interior of small pipes. The additively manufactured mirror is used in the metrology system to create a defined sampling signal within the cavity. Thereby the sensor system generates a point cloud of the internal surfaces using a 3D acquisition algorithm based on the laser triangulation principle. Part of this contribution will be the setup, the 3D acquisition and calibration principle as well as an evaluation of the metrology system. To optimize the point cloud acquisition three different hardware setups were designed using different cameras and calibration algorithms. These three approaches are evaluated and compared.
Focusing on the manufacturing and post processing steps the process chain to fabricate the miniaturized mirror is described. This includes an evaluation of the mirror based on roughness measurements. The reflectors are later utilized in a miniaturized sensor system to scan the interior of small pipes. The additively manufactured mirror is used in the metrology system to create a defined sampling signal within the cavity. Thereby the sensor system generates a point cloud of the internal surfaces using a 3D acquisition algorithm based on the laser triangulation principle. Part of this contribution will be the setup, the 3D acquisition and calibration principle as well as an evaluation of the metrology system. To optimize the point cloud acquisition three different hardware setups were designed using different cameras and calibration algorithms. These three approaches are evaluated and compared.
Platform for 3D inline process control in additive manufacturing
Show abstract
3D - Inline - Process - Control is getting more attention in any fields of manufacturing processes to increase productivity
and quality. Sensor systems are necessary to capture the currently process status and are basement for Inline-Process-
Control. The presented work is a possibility to get inline information’s about the additive manufacturing process Fused
Filament Fabrication. The requirement is the ability to manipulate the machine code to get free field of view to the
topside of the object after every manufactured layer. The adaptable platform layout makes possible to create different
approaches for inline process control. One approach is the single camera layout from bird view to get 2,5D information’s
about the manufactured object and the other one is the active stereoscopic camera layout with pattern projection. Both
approaches are showing a possibility to get information’s of the manufactured object in process. Additional this cases
allow a view inside the manufactured object and defects can be located. Deviations in the manufacturing process can be
corrected and relevant parameters can be adapted during slicing process to increase the manufacturing quality.
Flexible registration method for light-stripe sensors considering sensor misalignments
Show abstract
In many application areas such as object reconstruction or quality assurance, it is required to completely or partly
measure the shape of an object or at least the cross section of the required object region. For complex geometries,
therefore, multiple views are needed to bypass undercuts respectively occlusions. Hence, a multi-sensor measuring
system for complex geometries has to consist of multiple light-stripe sensors that are surrounding the measuring
object in order to complete the measurements in a prescribed time. The number of sensors depends on the
object geometry and dimensions. In order to create a uniform 3D data set from the data of individual sensors,
a registration of each individual data set into a common global coordinate system has to be performed. Stateof-
the-art registration methods for light-stripe sensors use only data from object intersection with the respective
laser plane of each sensor. At the same time the assumption is met that all laser planes are coplanar and that there
are corresponding points in two data sets. However, this assumption does not represent the real case, because it
is nearly impossible to align multiple laser planes in the same plane. For this reason, sensor misalignments are
neglected by this assumption. In this work a new registration method for light-stripe sensors is presented that
considers sensor misalignments as well as intended sensor displacements and tiltings. The developed method
combines 3D pose estimation and triangulated data to properly register the real sensor pose in 3D space.
Fringe Projection II
Suppression of contrast-related artefacts in phase-measuring structured light techniques
Show abstract
Optical metrology using phase measurements has benefited significantly from the introduction of phase-shifting
methods, first in interferometry, then also in fringe projection and fringe reflection. As opposed to interferometry, the
latter two techniques generally use a spatiotemporal phase-shifting approach: A sequence of fringe patterns with varying
spacing is used, and a phase map of each is generated by temporal phase shifting, to allow unique assignments of
projector or screen pixels to camera pixels. One ubiquitous problem with phase-shifting structured-light techniques is
that phase artefacts appear near regions of the image where the modulation amplitude of the projected or reflected fringes
changes abruptly, e.g. near dirt/dust particles on the surface in deflectometry or bright-dark object colour transitions in
fringe projection. Near the bright-dark boundaries, responses in the phase maps appear that are not plausible as actual
surface features. The phenomenon has been known for a long time but is usually ignored because it does not compromise
the overall reliability of results. In deflectometry, however, often the objective is to find and classify small defects, and
of course it is then important to distinguish between bogus phase responses caused by fringe modulation changes, and
actual surface defects. We present, for what we believe is the first time, an analytical derivation of the error terms, study
the parameters influencing the phase artefacts (in particular the fringe period), and suggest some simple algorithms to
minimise them.
3D geometry measurement of hot cylindric specimen using structured light
Show abstract
We present a fringe projection system to measure glowing hot hybrid components in between production processes. For this a high power green light projector, based on TI DLP technology, is used to create the highest possible contrast between fringes on the red glowing specimen. It has a resolution of 1140 x 912 pixels with a maximum frame rate of 120 images per second for fast measurement. We use a green bandpass filter (525 nm) on the camera lens to block unwanted incoming radiation from the specimen caused by self-emission. Commercial measurement standards are not calibrated for temperatures other than 20° C, so they cannot be used to validate measurement data at the required temperatures of up to 1000°C since thermal expansion invalidates the geometry specification from the calibration data sheet. In our first development we use a uniformly heated pipe made of stainless steel as a dummy specimen to examine the measured geometry data. A pyrometer measures the temperature of the pipe so the expansion can be easily calculated using the thermal expansion coefficient. Different impact and triangulation angles are investigated to identify the effects of hot ambient air on the measurement. The impact of the induced refractive index gradient is examined to check the need for pre-processing steps in the measurement routine.
Phase retrieval for high-speed 3D measurement using binary patterns with projector defocusing
Show abstract
Recent digital technology allows binary patterns to be projected with a very high speed, which shows great potential for
high-speed 3D measurement. However, how to retrieve an accurate phase with an even faster speed is still challenging.
In this paper, an accurate and efficient phase retrieval technique is presented, which combines a Hilbert three-step phaseshifting
algorithm with a ternary Gray code-based phase unwrapping method. The Hilbert three-step algorithm uses three
squared binary patterns, which can calculate an accurate phase even under a slight defocusing level. The ternary Gray
code-based method uses four binary patterns, which can unwrap a phase with a large number of fringe periods. Both
simulations and experiments have validated its accuracy and efficiency.
Experimental comparison of photogrammetry for additive manufactured parts with and without laser speckle projection
Show abstract
In this paper we show that, by using a photogrammetry system with and without laser speckle, a large range of additive
manufacturing (AM) parts with different geometries, materials and post-processing textures can be measured to high
accuracy. AM test artefacts have been produced in three materials: polymer powder bed fusion (nylon-12), metal powder
bed fusion (Ti-6Al-4V) and polymer material extrusion (ABS plastic). Each test artefact was then measured with the
photogrammetry system in both normal and laser speckle projection modes and the resulting point clouds compared with
the artefact CAD model. The results show that laser speckle projection can result in a reduction of the point cloud
standard deviation from the CAD data of up to 101 μm. A complex relationship with surface texture, artefact geometry
and the laser speckle projection is also observed and discussed.
Special Session: Spectroscopic Techniques in Industrial and Astronomical Applications
Comparison of astrophysical laser frequency combs with respect to the requirements of HIRES
Show abstract
Precise astronomical spectroscopy with the forthcoming E-ELT and its high resolution spectrograph HIRES will address a number of important science cases,1 e.g. detection of atmospheres of exoplanets. Challenging technical requirements have been identified to achieve these cases, principal among which is the goal to achieve a radial velocity precision on the order of 10 cms-1. HIRES will experience systematic errors like intrapixel variations and random variations like fiber noise, caused by the non-uniform illumination of the coupling fibers, with these and other systematic errors affecting the performance of the spectrograph. Here, we describe the requirements for the calibration sources which may be used for mitigating such systematic errors in HIRES. Precise wavelength calibration with wide-mode-spacing laser frequency combs (LFCs), so called astrocombs, has been demonstrated with different astronomical spectrographs. Here we present a comparison of currently used astrocombs and outline a possible solution to meet the requirements of HIRES with a single broadband astrocomb.
The end-to-end simulator for the E-ELT HIRES high resolution spectrograph
Show abstract
We present the design, architecture and results of the End-to-End simulator model of the high resolution spectrograph
HIRES for the European Extremely Large Telescope (E-ELT). This system can be used as a tool to characterize the
spectrograph both by engineers and scientists. The model allows to simulate the behavior of photons starting from the
scientific object (modeled bearing in mind the main science drivers) to the detector, considering also calibration light
sources, and allowing to perform evaluation of the different parameters of the spectrograph design. In this paper, we will
detail the architecture of the simulator and the computational model which are strongly characterized by modularity and
flexibility that will be crucial in the next generation astronomical observation projects like E-ELT due to of the high
complexity and long-time design and development. Finally, we present synthetic images obtained with the current
version of the End-to-End simulator based on the E-ELT HIRES requirements (especially high radial velocity accuracy).
Once ingested in the Data reduction Software (DRS), they will allow to verify that the instrument design can achieve the
radial velocity accuracy needed by the HIRES science cases.
Atomic layer sensitive in-situ plasma etch depth control with reflectance anisotropy spectroscopy (RAS)
Show abstract
Reflectance anisotropy spectroscopy (RAS) allows for in-situ monitoring of reactive ion etching (RIE) of
monocrystalline III-V semiconductor surfaces. Upon use of RAS the sample to be etched is illuminated with broad-band
linearly polarized light under nearly normal incidence. Commonly the spectral range is between 1.5 and 5.5 eV.
Typically the spectrally resolved difference in reflectivity for light of two orthogonal linear polarizations of light is
measured with respect to time - for example for cubic lattices (like the zinc blende structures of most III-V
semiconductors) polarizations along the [110] and the [-110] direction. Local anisotropies on the etch front cause
elliptical polarization of the reflected light resulting in the RAS signal. The time and photon energy resolved spectra of
RAS include reflectometric as well as interferometric information. Light with wavelengths well above 100 nm (even
inside the material) can be successfully used to monitor surface abrasion with a resolution of some tens of nanometers.
The layers being thinned out act as optical interferometers resulting in Fabry-Perot oscillations of the RAS-signal. Here
we report on RAS measurements assessing the surface deconstruction during dry etching. For low etch rates our
experimental data show even better resolution than that of the (slow) Fabry-Perot oscillations. For certain photon
energies we detect monolayer-etch-related oscillations in the mean reflectivity, which give the best possible resolution in
etch depth monitoring and control, i.e. the atomic scale.
Photo-vibrational spectroscopy using quantum cascade laser and laser Doppler vibrometer
Huan Liu,
Qi Hu,
Jiecheng Xie,
et al.
Show abstract
Photoacoustic/photothermal spectroscopy is an established technique for detection of chemicals and explosives.
However, prior sample preparation is required and the analysis is conducted in a sealed space with a high-sensitivity
sensor coupled with a lock-in amplifier, limiting the technique to applications in a controllable laboratory environment.
Hence, this technique may not be suitable for defense and security applications where the detection of explosives or
hazardous chemicals is required in an open environment at a safe standoff distance. In this study, chemicals in various
forms were excited by an intensity-modulated quantum cascade laser (QCL), while a laser Doppler vibrometer (LDV)
was applied to detect the vibration signal resulting from the photocoustic/photothermal effect. The photo-vibrational
spectrum obtained by scanning the QCL’s wavelength in MIR range, coincides well with the corresponding spectrum
obtained using typical FTIR equipment. The experiment in short and long standoff distances demonstrated that the LDV
is a capable sensor for chemical detection in an open environment.
High-Resolution Profiling I
Three-dimensional Dammann confocal microscopy
Show abstract
Three-dimensional (3D) Dammann confocal microscopy is proposed based on introducing 3D Dammann gratings into
traditional confocal microscopy. The conventional confocal microscopy usually has a single focal point. Using threedimensional
Dammann gratings, it shows a new confocal microscopy which could obtain three-dimensional information
of object, therefore, novel Dammann-based microscopy should be developed for practical applications.
Optical inspection of hidden MEMS structures
Show abstract
Micro-electro-mechanical system's (MEMS) applications have greatly expanded over the recent years, and the MEMS industry has grown almost exponentially. One of the strongest drivers are the automotive and consumer markets. A 100% test is necessary especially in the production of automotive MEMS sensors since they are subject to safety relevant functions. This inspection should be carried out before dicing and packaging since more than 90% of the production costs are incurred during these steps. An electrical test is currently being carried out with each MEMS component. In the case of a malfunction, the defect can not be located on the wafer because the MEMS are no longer optically accessible due to the encapsulation. This paper presents a low coherence interferometer for the topography measurement of MEMS structures located within the wafer stack. Here, a high axial and lateral resolution is necessary to identify defects such as stuck or bent MEMS fingers. First, the boundary conditions for an optical inspection system will be discussed. The setup is then shown with some exemplary measurements.
Confocal unrolled areal measurements of cylindrical surfaces
Show abstract
Confocal microscopes are widely used for areal measurements thanks to its good height resolution and the capability to
measure high local slopes. For the measurement of large areas while keeping few nm of system noise, it is needed to use
high numerical aperture objectives, move the sample in the XY plane and stitch several fields together to cover the
required surface. On cylindrical surfaces a rotational stage is used to measure fields along the round surface and stitch
them in order to obtain a complete 3D measurement. The required amount of fields depends on the microscope’s
magnification, as well as on the cylinder diameter. However, for small diameters, if the local shape reaches slopes not
suitable for the objective under use, the active field of the camera has to be reduced, leading to an increase of the
required number of fields to be measured and stitched. In this paper we show a new approach for areal measurements of
cylindrical surfaces that uses a rotational stage in combination with a slit projection confocal arrangement and a highspeed
camera. An unrolled confocal image of the cylinder surface is built by rotating the sample and calculating the
confocal intensity in the centre of the slit using a gradient algorithm. A set of 360º confocal images can be obtained at
different heights of the sample relative to the sensor and used to calculate an unrolled areal measure of the cylinder. This
method has several advantages over the conventional one such as no stitching required, or reduced measurement time. In
addition, the result shows less residual flatness error since the surface lies flat in the measurement direction in
comparison to field measures where the highest slope regions will show field distortion and non-constant sampling. We
have also studied the influence on the areal measurements of wobble and run-out introduced by the clamping mechanism
and the rotational axis.
Transfer characteristics of optical profilers with respect to rectangular edge and step height measurement
Show abstract
Optical profilers are mature instruments used in research and industry to study surface topography features. Although the corresponding standards are based on simple step height measurements, in practical applications these instruments are often used to study the fidelity of surface topography.
In this context it is well-known that in certain situations a surface profile obtained by an optical profiler will differ from the real profile. With respect to practical applications such deviations often occur in the vicinity of steep walls and in cases of high aspect ratio.
In this contribution we compare the transfer characteristics of different 3D optical profiler principles, namely white-light interferometry, focus sensing, and confocal microscopy. Experimental results demonstrate that the transfer characteristics do not only depend on the parameters of the optical measurement system (e. g. wavelength and coherence of light, numerical aperture, evaluated signal feature, polarization) but also on the properties of the measuring object such as step height, aspect ratio, material properties and homogeneity, rounding and steepness of the edges, surface roughness. As a result, typical artefacts such as batwings occur for certain parameter combinations, particularly at certain height-to-wavelength ratio (HWR) values. Understanding of the mechanisms behind these phenomena enables to reduce them by an appropriate parameter adaption. However, it is not only the edge artefacts, but also the position of an edge that may be changed due to the properties of the measuring object.
In order to investigate the relevant effects theoretically, several models are introduced. These are based on either an extension of Richards-Wolf modeling or rigorous coupled wave analysis (RCWA). Although these models explain the experimental effects quite well they suffer from different limitations, so that a quantitative correspondence of theoretical modeling and experimental results is hard to achieve.
Nevertheless, these models are used to study the characteristics of the measured signals occurring at edges of different step height compared to signals occurring at plateaus. Moreover, a special calibration sample with continuous step height variation was developed to reduce the impact of unknown sample properties. We analyzed the signals in both, the spatial and the spatial frequency domain, and found systematic signal changes that will be discussed. As a consequence, these simulations will help to interpret measurement results appropriately and to improve them by proper parameter settings and calibration and finally to increase the edge detection accuracy.
In this context it is well-known that in certain situations a surface profile obtained by an optical profiler will differ from the real profile. With respect to practical applications such deviations often occur in the vicinity of steep walls and in cases of high aspect ratio.
In this contribution we compare the transfer characteristics of different 3D optical profiler principles, namely white-light interferometry, focus sensing, and confocal microscopy. Experimental results demonstrate that the transfer characteristics do not only depend on the parameters of the optical measurement system (e. g. wavelength and coherence of light, numerical aperture, evaluated signal feature, polarization) but also on the properties of the measuring object such as step height, aspect ratio, material properties and homogeneity, rounding and steepness of the edges, surface roughness. As a result, typical artefacts such as batwings occur for certain parameter combinations, particularly at certain height-to-wavelength ratio (HWR) values. Understanding of the mechanisms behind these phenomena enables to reduce them by an appropriate parameter adaption. However, it is not only the edge artefacts, but also the position of an edge that may be changed due to the properties of the measuring object.
In order to investigate the relevant effects theoretically, several models are introduced. These are based on either an extension of Richards-Wolf modeling or rigorous coupled wave analysis (RCWA). Although these models explain the experimental effects quite well they suffer from different limitations, so that a quantitative correspondence of theoretical modeling and experimental results is hard to achieve.
Nevertheless, these models are used to study the characteristics of the measured signals occurring at edges of different step height compared to signals occurring at plateaus. Moreover, a special calibration sample with continuous step height variation was developed to reduce the impact of unknown sample properties. We analyzed the signals in both, the spatial and the spatial frequency domain, and found systematic signal changes that will be discussed. As a consequence, these simulations will help to interpret measurement results appropriately and to improve them by proper parameter settings and calibration and finally to increase the edge detection accuracy.
Focus-variation microscopy for measurement of surface roughness and autocorrelation length
Erich Grossman
Show abstract
Spatial bandwidth limitations frequently introduce large biases into the estimated values of RMS roughness and
autocorrelation length that are extracted from topography data on random rough surfaces. The biases can be particularly
severe for focus-variation microscopy data because of the technique’s spatial bandwidth limitations (limited lateral
resolution and field-of-view). We recently developed a measurement protocol that greatly reduces the bias due to limited
resolution[1]. In the present paper, we describe an extension of the protocol to correct for limited field-of-view, and present
measurements on a series of commercial surface roughness comparator samples to validate the protocol. The protocol
strictly applies to the case of surfaces that are isotropic, and whose topography displays an autocovariance function that is
exponential, with a single autocorrelation length. However, we find that applying the protocol yields extracted values of
roughness and autocorrelation length for each surface that are accurate and consistent among datasets obtained at different
magnifications (i.e. among datasets obtained with different spatial bandpass limits), even for samples that are not in any
way selected to conform to the model’s assumptions.
High-Resolution Profiling II
Sub-diffraction surface topography measurement using a microsphere-assisted Linnik interferometer
Show abstract
Microscopic surface topography measurement is an important aspect of industrial inspection. Optical and near field
scanning techniques are increasingly replacing the use of the traditional mechanical stylus since they provide better lateral
resolutions and higher measurement speeds. The main far field optical techniques used are interference microscopy and
confocal microscopy, with the advantages of having larger fields of view and higher measurement speeds. Interference
microscopy is now widely used, mainly because of its nanometric axial measurement sensitivity and its ease of use but
suffers from a limitation in lateral resolution of about /2 due to diffraction. A new technique for high resolution 2D
imaging using a microsphere placed on the sample has been recently combined with interferometry by several groups to
greatly improve the lateral resolution. In this paper we present some of our own first results using glass microspheres with
a white light Linnik interferometer and demonstrate a lateral resolution of /4 and an axial measurement sensitivity of
several nm. Results are shown on calibrated square profile gratings with periods down to 400 nm, with a minimum feature
size of 200 nm and a height of 148 nm and a field of view of several μm. While these features are not visible directly with
the microscope objective, they become observable and measurable through the microsphere. An analysis using rigorous
electromagnetic simulations is also given to help better understand the imaging properties of the technique. These first
experimental and simulation results clearly indicate that this is an important new technique that opens new possibilities for
surface metrology with a lateral resolution well beyond the diffraction limit.
Measurement, certification and use of step-height calibration specimens in optical metrology
Show abstract
Calibration, adjustment and verification of surface topography measuring instruments are important tasks, often facilitated by precision step-height specimens that have been calibrated using traceable metrology such as interferometry. Although standardized procedures for calculating parameters of the step-height are available for line profiling contact stylus systems, there is inconsistent guidance as to how to interpret step height data for 3D, areal surface topography instruments, such as confocal and interference microscopes. Here we provide definitions for the reference and measurement areas of step-height specimens as well as practical measurement protocols for processing the surface topography map.
Surface profile measurement by using the integrated Linnik WLSI and confocal microscope system
Show abstract
The white-light scanning interferometer (WLSI) and confocal microscope (CM) are the two major optical inspection
systems for measuring three-dimensional (3D) surface profile (SP) of micro specimens. Nevertheless, in practical
applications, WLSI is more suitable for measuring smooth and low-slope surfaces. On the other hand, CM is more suitable
for measuring uneven-reflective and low-reflective surfaces. As for aspect of surface profiles to be measured, the
characteristics of WLSI and CM are also different. WLSI is generally used in semiconductor industry while CM is more
popular in printed circuit board industry. In this paper, a self-assembled multi-function optical system was integrated to
perform Linnik white-light scanning interferometer (Linnik WLSI) and CM. A connecting part composed of tubes, lenses
and interferometer was used to conjunct finite and infinite optical systems for Linnik WLSI and CM in the self-assembled
optical system. By adopting the flexibility of tubes and lenses, switching to perform two different optical measurements
can be easily achieved. Furthermore, based on the shape from focus method with energy of Laplacian filter, the CM was
developed to enhance the on focal information of each pixel so that the CM can provide all-in-focus image for performing
the 3D SP measurement and analysis simultaneously. As for Linnik WLSI, eleven-step phase shifting algorithm was used
to analyze vertical scanning signals and determine the 3D SP.
Super-resolution photonic nanojet interferometry: photonic nanojet interaction with a polymer sample
Show abstract
Super-resolution photonic nanojet interferometry is a new modality for 3D label-free super-resolution imaging. We
present a comparative study of the photonic nanojet interaction with a polymer sample. We use numerical modelling to
understand the interaction between a microsphere-induced photonic nanojet and the polymer sample. The numerical
model employs the same set of input parameters (melamine formaldehyde microsphere with a diameter of 11 μm and a
refractive index of 1.68), as in our experiments. The interaction is described using the Finite-Difference Time-Domain
method applied on a finely discretized mesh. The knowledge gained using the verified and validated model, will be used
to conduct numerical simulations in a wider parameter space. This enables optimizing the design of 3D-interferometric
super-resolution microscopes.
Joint Session I: High-Precision Measurement of Optical Components and Systems
Combination of a fast white-light interferometer with a phase shifting interferometric line sensor for form measurements of precision components
Show abstract
By means of an interferometric line sensor system, the form of a specimen can be measured by stitching several
overlapping circular subapertures to form one 3D topography. This concept is very flexible and can be adapted to many
different specimen geometries. The sensor is based on a Michelson interferometer configuration that consists of a rapidly
oscillating reference mirror in combination with a high-speed line-scan camera. Due to the overlapping areas, movement
errors of the scan axes can be corrected.
In order to automatically adjust the line sensor in such a way that it is perpendicular to the measurement surface at a fixed working distance, a white-light interferometer was included in the line-based form-measuring system. By means of a fast white-light scan, the optimum angle of the sensor (with respect to the surface of the specimen) is determined in advance, before scanning the specimen using the line-based sinusoidal phase shifting interferometer. This produces accurate measurement results and makes it possible to also measure non-rotational specimens.
In this paper, the setup of the line-based form-measuring system is introduced and the measurement strategy of the sensor adjustment using an additional white-light interferometer is presented. Furthermore, the traceability chain of the system and the main error influences are discussed. Examples of form measurement results are shown.
In order to automatically adjust the line sensor in such a way that it is perpendicular to the measurement surface at a fixed working distance, a white-light interferometer was included in the line-based form-measuring system. By means of a fast white-light scan, the optimum angle of the sensor (with respect to the surface of the specimen) is determined in advance, before scanning the specimen using the line-based sinusoidal phase shifting interferometer. This produces accurate measurement results and makes it possible to also measure non-rotational specimens.
In this paper, the setup of the line-based form-measuring system is introduced and the measurement strategy of the sensor adjustment using an additional white-light interferometer is presented. Furthermore, the traceability chain of the system and the main error influences are discussed. Examples of form measurement results are shown.
Birefringence measurement in complex optical systems
Show abstract
State of the art optical systems become more complex. There are more lenses required in the optical design
and optical coatings have more layers. These complex designs are prone to induce more thermal stress into the optical
system which causes birefringence. In addition, there is a certain degree of freedom required to meet optical specifications
during the assembly process. The mechanical fixation of these degrees of freedom can also lead to mechanical stress in
the optical system and therefore to birefringence. To be able to distinguish those two types of stress a method to image
the birefringence in the optical system is required. In the proposed setup light is polarized by a circular polarization filter
and then is transmitted through a rotatable linear retarder and the tested optical system. The light then is reflected on the
same path by a mirror. After the light passes the circular polarization filter on the way back, the intensity is recorded.
When the rotatable retarder is rotated, the recorded intensity is modulated depending on the birefringence of the tested
optical system. This modulation can be analyzed in Fourier domain and the linear retardance angle between the slow and
the fast axis as well as the angle of the fast axis can be calculated. The retardance distribution over the pupil of the optical
system then can be analyzed using Zernike decomposition. From the Zernike decomposition, the origin of the birefringence
can be identified. Since it is required to quantify small amounts of retardance well below 10nm, the birefringence of the
measurement system must be characterized before the measurement and considered in the calculation of the resulting
birefringence. Temperature change of the measurement system still can produce measurement artifacts in the calculated
result, which must also be compensated for.
Joint Session II: High-Precision Measurement of Optical Components and Systems
Dynamic interferometry: measurement of space optics and structures
Show abstract
Over the last two decades the use of single-frame interferometric techniques, known as Dynamic Interferometry, has
become widely available in commercial interferometer systems and they have been used extensively in the production of
state-of-the-art space-based optical systems. This paper presents an overview of the techniques and configurations used
to build dynamic interferometers and measurement results for a variety of space-based optical components as well as the
structures that hold them under simulated space-flight conditions. These techniques and configurations have applicability
for many non-space applications as well.
Preliminary results of a new proposal for objective human independent striae measurement
Show abstract
Optical glasses with certain inner quality e.g. low striae content are essential for good optical systems. A stria is a small
local change in the refractive index inside the glass resulting in a wave front distortion that can cause blurring of the image.
During the production process of optical glass, striae are observed by measuring it with the so-called shadow graph method.
This simple measurement displays a stria as a shadow on an observation screen. A human operator evaluates the contrast
by comparing it with references. The new proposed approach uses a digital camera and image processing to measure human
independent the stria level. A first repeatability measurement shows wave front deviation (maximum deviation, peak-topeak)
of less than +/- 8 nm.
Development of metrology for freeform optics in reflection mode
Show abstract
The increased range of manufacturable freeform surfaces offered by the new fabrication techniques is giving
opportunities to incorporate them in the optical systems. However, the success of these fabrication techniques depends
on the capabilities of metrology procedures and a feedback mechanism to CNC machines for optimizing the
manufacturing process. Therefore, a precise and in-situ metrology technique for freeform optics is in demand. Though
all the techniques available for aspheres have been extended for the freeform surfaces by the researchers, but none of the
techniques has yet been incorporated into the manufacturing machine for in-situ measurement. The most obvious reason
is the complexity involved in the optical setups to be integrated in the manufacturing platforms. The Shack-Hartmann
sensor offers the potential to be incorporated into the machine environment due to its vibration insensitivity, compactness
and 3D shape measurement capability from slope data. In the present work, a measurement scheme is reported in which a
scanning Shack-Hartmann Sensor has been employed and used as a metrology tool for measurement of freeform surface
in reflection mode. Simulation studies are conducted for analyzing the stitching accuracy in presence of various
misalignment errors. The proposed scheme is experimentally verified on a freeform surface of cubic phase profile.
Speckle Metrology
Deformation measurements by ESPI of the surface of a heated mirror and comparison with numerical model
Show abstract
The manufacture of mirrors for space application is expensive and the requirements on the optical performance increase
over years. To achieve higher performance, larger mirrors are manufactured but the larger the mirror the higher the
sensitivity to temperature variation and therefore the higher the degradation of optical performances. To avoid the use of
an expensive thermal regulation, we need to develop tools able to predict how optics behaves with thermal constraints.
This paper presents the comparison between experimental surface mirror deformation and theoretical results from a
multiphysics model. The local displacements of the mirror surface have been measured with the use of electronic speckle
pattern interferometry (ESPI) and the deformation itself has been calculated by subtracting the rigid body motion. After
validation of the mechanical model, experimental and numerical wave front errors are compared.
Reduction of phase singularities in a speckle Michelson setup
Show abstract
Speckle interferometry is an optical metrology technique for characterizing rough surfaces. In one application, the
deformation of a specimen under a load may be determined by comparing measurements before and after the load is
applied. Owing to the surface roughness, however, the results are impaired by phase singularities, leading to a strong
noise in the measurement results. Usually, filtering and smoothing operations are performed to reduce the noise.
However, these procedures also affect the underlying systematic phase and are therefore disadvantageous. Instead, we
examine incoherent averaging, a physical procedure, to reduce the number of phase singularities in the first place. We
tailor the spatial coherence of the light using extended light sources of continuous or multipoint shape, achieving
smoother phase distributions. The mechanism behind the reduction process involves subtle effects like enhancing phase
singularity correlations in the fields before and after the deformation takes place.
Speckle-interferometric measurement system of 3D deformation to obtain thickness changes of thin specimen under tensile loads
Show abstract
The analysis of materials and geometries in tensile tests and the extraction of mechanic parameters is an important field
in solid mechanics. Especially the measurement of thickness changes is important to obtain accurate strain information of
specimens under tensile loads. Current optical measurement methods comprising 3D digital image correlation enable
thickness-change measurement only with nm-resolution. We present a phase-shifting electronic speckle-pattern
interferometer in combination with speckle-correlation technique to measure the 3D deformation. The phase-shift for the
interferometer is introduced by fast wavelength tuning of a visible diode laser by injection current. In a post-processing
step, both measurements can be combined to reconstruct the 3D deformation. In this contribution, results of a 3Ddeformation
measurement for a polymer membrane are presented. These measurements show sufficient resolution for the
detection of 3D deformations of thin specimen in tensile test. In future work we address the thickness changes of thin
specimen under tensile loads.
Uncertainty of scattered light roughness measurements based on speckle correlation methods
Show abstract
Surface micro topography measurement (e.g., form, waviness, roughness) is a precondition to assess the surface quality
of technical components with regard to their applications. Well defined, standardized measuring devices measure and
specify geometrical surface textures only under laboratory conditions. Laser speckle-based roughness measurement is a
parametric optical scattered light measuring technique that overcomes this confinement. Field of view dimensions of
some square millimeters and measuring frequencies in the kHz domain enable in-process roughness characterization of
even moving part surfaces. However, camera exposure times of microseconds or less and a high detector pixel density
mean less light energy per pixel due to the limited laser power. This affects the achievable measurement uncertainty
according to the Heisenberg uncertainty principle. The influence of fundamental, inevitable noise sources such as the
laser shot noise and the detector noise is not quantified yet. Therefore, the uncertainty for speckle roughness
measurements is analytically estimated. The result confirms the expected inverse proportionality of the measurement
uncertainty to the square root of the illuminating light power and the direct proportionality to the detector readout noise,
quantization noise and dark current noise, respectively. For the first time it is possible to quantify the achievable
measurement uncertainty u(Sa) < 1 nm for the scattered light measuring system. The low uncertainty offers ideal
preconditions for in-process roughness measurements in an industrial environment with an aspired resolution of 1 nm.
Pre-treatment for preventing degradation of measurement accuracy by speckle noise in speckle interferometry
Show abstract
The deformation measurement method by using only two speckle patterns has been proposed in ESPI (electronic speckle
pattern interferometry) by using Fourier transform. Furthermore, three-dimensional deformation of the object was able to
be measured with the same sensitivities in each direction of three-dimensional axis. However, the measurement results of
a complex shape deformation are not always a smooth distribution of phase map. It can be thought that this trouble is
caused from the effect of speckle noise which is included in speckle pattern. In this paper, the solution of the problem
concerning the speckle noise is investigated. The degradation of measurement accuracy in speckle interferometry is
caused by some speckle noise. The speckle noise influences the bias component and the amplitude of the speckle pattern.
Furthermore, the spatial movement of speckles of speckle-pattern during the deformation process also influences into the
measurement accuracy. In this paper, the pre-treatment for the speckle interferometry is proposed in order to reduce such
influence by speckle noise. In the experimental results, it is confirmed that the influence of speckle noise can be reduced
by using the features of the reference and the object beams’ intensity distributions in interference measurement process.
The proposed method can reduce the influence of speckle noise to 1/1000 in comparing with the results of conventional
method. The validity of the proposed method in the practical operation is confirmed from the experiments.
In-situ and Nondestructive Testing I
Optical residual stress measurement in TFT-LCD panels
Show abstract
The residual stress of the glass substrate might be one of causes to produce the non-uniform light distribution defect, i.e.
Mura, in thin film transistor-liquid crystal display (TFT-LCD) panels. Glass is a birefringent material with very low
birefringence. Furthermore, the thinner and thinner thickness request from the market makes the traditional
photoelasticity almost impossible to measure the residual stresses produced in thin glass plates. Recently, a low-level
stress measurement method called transmissivity extremities theory of photoelasticity (TEToP) was successfully
developed to measure the residual stress in glass plate. Besides, to measure the stress of the glass plate in the TFT-LCD
panel whose rear surface may has different kinds of coatings, an advanced reflection photoelasticity was also developed.
In this paper, three commercially available glass plates with 0.33mm nominal thickness and three glass circular disks
with different coatings were inspected to verify the feasibility of the TEToP and the advanced reflection photoelasticity,
respectively.
Calibration of the incident beam in a reflective topography measurement from an unknown surface
Show abstract
The precision of measurements as well as the need for precise measurements are increasing more and more. Thus, the
importance of a good calibration of a setup is increasing, too. In the world of topography measurement a huge variety of
techniques are available. Some of these techniques are using known shadow patterns reflected by the device under test
(DUT). The reflected patterns are recorded using a camera with imaging optics. From the changes of the patterns, the
topography can be resolved. Other measurement techniques are using a tactile sensing head, which is in contact with the
surface to determine its topography. However, these techniques need a reference surface to calibrate movements. If this
reference surface presents deviations from its expected form, errors are introduced.
We have developed a calibration method for reflective surface measurements based on experimental ray tracing (ERT) without the need of a reference surface. In our measurement setup, a narrow laser beam introduced in the measurement under a certain angle is reflected by the device under test. After the reflection the position and the direction of the ray in terms of the coordinate system of the camera is detected. Thus, no errors are introduced by using an additional imaging optic. To calibrate position and direction of the incident ray in respect to the coordinate system of the camera, the reflected rays from the measurement are used only. From these rays, the incident ray is determined by detecting the line, all reflected rays are intersecting with. This leads to two major advantages. First, there is no calibration run needed, since the measurement data can be used directly for the calibration. Second, for the calibration no well-known reference surface is needed. However, some regulations have to be considered for a stable process of this calibration method. In terms of peak-to-valley values of the sag of the surface as well as of the change of the surface slope, the surface has to show values deviating from zero. If a surface like this is measured, a separate measurement run can be performed using another surface fulfilling these requirements. Since the DUT is scanned by moving the DUT itself, the position and the direction of the incident ray is not changed from one measurement to another and can be reused. We describe the newly introduced calibration method for the incident ray in detail and present the necessary boundary conditions. The calibration has been tested using simulations and has been implemented in a measurement setup. Within this measurement setup, the expected performance resulting from the simulations has been examined.
We have developed a calibration method for reflective surface measurements based on experimental ray tracing (ERT) without the need of a reference surface. In our measurement setup, a narrow laser beam introduced in the measurement under a certain angle is reflected by the device under test. After the reflection the position and the direction of the ray in terms of the coordinate system of the camera is detected. Thus, no errors are introduced by using an additional imaging optic. To calibrate position and direction of the incident ray in respect to the coordinate system of the camera, the reflected rays from the measurement are used only. From these rays, the incident ray is determined by detecting the line, all reflected rays are intersecting with. This leads to two major advantages. First, there is no calibration run needed, since the measurement data can be used directly for the calibration. Second, for the calibration no well-known reference surface is needed. However, some regulations have to be considered for a stable process of this calibration method. In terms of peak-to-valley values of the sag of the surface as well as of the change of the surface slope, the surface has to show values deviating from zero. If a surface like this is measured, a separate measurement run can be performed using another surface fulfilling these requirements. Since the DUT is scanned by moving the DUT itself, the position and the direction of the incident ray is not changed from one measurement to another and can be reused. We describe the newly introduced calibration method for the incident ray in detail and present the necessary boundary conditions. The calibration has been tested using simulations and has been implemented in a measurement setup. Within this measurement setup, the expected performance resulting from the simulations has been examined.
Error influences of the shear element in interferometry for form characterization of optics
Show abstract
A shearing interferometer combined with an LED multispot illumination provides a high flexibility form characterization
of optical surfaces as it is needed for aspheres and freeforms. Core element of the setup is the spatial light modulator as
shearing element (SLM). Error influences due to the used blazed grating of the SLM need to be investigated. We show
results of wavefront measurements with a Shack-Hartmann sensor which demonstrate residual structures of the grating at
the wavefront under test. Additionally, simulated data are compared to the measurements to get a better understanding of
the expected effects. These investigations help to correct the wavefront under test for this static error and improve the
accuracy of the form characterisation.
An endoscopic shearography system with radial sensitivity for inner inspection of adhesion faults in composite material pipes
Show abstract
This work presents the development of a special shearography system with radial sensitivity and explores its applicability
for detecting adhesion flaws on internal surfaces of joints of composite material pipes. The system uses two conical mirrors
to achieve radial sensitivity. A primary 45° conical mirror is responsible for promoting the inspection of the internal surface
all way around 360°. A special Michelson-like interferometer is formed replacing one of the plane mirrors by a conical
mirror. The image reflected by this conical mirror is shifted away from the image center in a radial way and a radial shear
is produced on the images. The concept was developed and tested. Two tubular steel specimens internally coated with
composite materials and having known artificial defects were analyzed to test the ability of the system to detect the flaws.
The system presented very good results on all inspected specimens. The experimental results obtained in this work are
promising and open a new front for inspections of inner surfaces of composite pipes with shearography.
Bulk strain solitons as a tool for determination of the third order elastic moduli of composite materials
Show abstract
We demonstrate an alternative approach to determination of the third order elastic moduli of materials based on
registration of nonlinear bulk strain waves in three basic structural waveguides (rod, plate and shell) and further
calculation of the Murnaghan moduli from the recorded wave parameters via simple algebra. These elastic moduli are
available in literature for a limited number of materials and are measured with considerable errors, that evidences a
demand in novel approaches to their determination.
In-situ and Nondestructive Testing II
Fiber Bragg grating sensors in harsh environments: considerations and industrial monitoring applications
Show abstract
Over the last few years, fiber optic sensors (FOS) have seen an increased acceptance and widespread use in industrial sensing and in structural monitoring in civil, aerospace, marine, oil & gas, composites and other applications. One of the most prevalent types in use today are fiber Bragg grating (FBG) sensors. Historically, FOS have been an attractive solution because of their EM immunity and suitability for use in harsh environments and rugged applications with extreme temperatures, radiation exposure, EM fields, high voltages, water contact, flammable atmospheres, or other hazards.
FBG sensors have demonstrated that can operate reliably in many different harsh environment applications but proper type and fabrication process are needed, along with suitable packaging and installation procedure. In this paper, we review the impact that external factors and environmental conditions play on FBG’s performance and reliability, and describe the appropriate sensor types and protection requirements suitable for a variety of harsh environment applications in industrial furnaces, cryogenic coolers, nuclear plants, maritime vessels, oil & gas wells, aerospace crafts, automobiles, and others.
FBG sensors have demonstrated that can operate reliably in many different harsh environment applications but proper type and fabrication process are needed, along with suitable packaging and installation procedure. In this paper, we review the impact that external factors and environmental conditions play on FBG’s performance and reliability, and describe the appropriate sensor types and protection requirements suitable for a variety of harsh environment applications in industrial furnaces, cryogenic coolers, nuclear plants, maritime vessels, oil & gas wells, aerospace crafts, automobiles, and others.
Measurement uncertainty budget of an interferometric flow velocity sensor
Show abstract
Flow rate measurements are a common topic for process monitoring in chemical engineering and food industry. To achieve the requested low uncertainties of 0:1% for flow rate measurements, a precise measurement of the shear layers of such flows is necessary. The Laser Doppler Velocimeter (LDV) is an established method for measuring local flow velocities. For exact estimation of the flow rate, the flow profile in the shear layer is of importance. For standard LDV the axial resolution and therefore the number of measurement points in the shear layer is defined by the length of the measurement volume. A decrease of this length is accompanied by a larger fringe distance variation along the measurement axis which results in a rise of the measurement uncertainty for the flow velocity (uncertainty relation between spatial resolution and velocity uncertainty). As a unique advantage, the laser Doppler profile sensor (LDV-PS) overcomes this problem by using two fan-like fringe systems to obtain the position of the measured particles along the measurement axis and therefore achieve a high spatial resolution while it still offers a low velocity uncertainty. With this technique, the flow rate can be estimated with one order of magnitude lower uncertainty, down to 0:05% statistical uncertainty.1 And flow profiles especially in film flows can be measured more accurately. The problem for this technique is, in contrast to laboratory setups where the system is quite stable, that for industrial applications the sensor needs a reliable and robust traceability to the SI units, meter and second. Small deviations in the calibration can, because of the highly position depending calibration function, cause large systematic errors in the measurement result. Therefore, a simple, stable and accurate tool is needed, that can easily be used in industrial surroundings to check or recalibrate the sensor. In this work, different calibration methods are presented and their influences to the measurement uncertainty budget of the sensor is discussed. Finally, generated measurement results for the film flow of an impinging jet cleaning experiment are presented.
Laser speckle velocimetry for robot manufacturing
Show abstract
A non-contact speckle correlation sensor for the measurement of robotic tool speed is presented for use in robotic manufacturing and is capable of measuring the in-plane relative velocities between a robot end-effector and the workpiece or other surface. The sensor performance was assessed in the laboratory with the sensor accuracies found to be better than 0:01 mm/s over a 70 mm/s velocity range. Finally an example of the sensors application to robotic manufacturing is presented where the sensor was applied to tool speed measurement for path planning in the wire and arc additive manufacturing process using a KUKA KR150 L110/2 industrial robot.
Non-invasive seedingless measurements of the flame transfer function using high-speed camera-based laser vibrometry
Show abstract
The characterization of modern jet engines or stationary gas turbines running with lean combustion by means of swirl-stabilized flames necessitates seedingless optical field measurements of the flame transfer function, i.e. the ratio of the fluctuating heat release rate inside the flame volume, the instationary flow velocity at the combustor outlet and the time average of both quantities. For this reason, a high-speed camera-based laser interferometric vibrometer is proposed for spatio-temporally resolved measurements of the flame transfer function inside a swirl-stabilized technically premixed flame. Each pixel provides line-of-sight measurements of the heat release rate due to the linear coupling to fluctuations of the refractive index along the laser beam, which are based on density fluctuations inside the flame volume. Additionally, field measurements of the instationary flow velocity are possible due to correlation of simultaneously measured pixel signals and the known distance between the measurement positions. Thus, the new system enables the spatially resolved detection of the flame transfer function and instationary flow behavior with a single measurement for the first time. The presented setup offers single pixel resolution with measurement rates up to 40 kHz at an maximum image resolution of 256 px x 128 px. Based on a comparison with reference measurements using a standard pointwise laser interferometric vibrometer, the new system is validated and a discussion of the measurement uncertainty is presented. Finally, the measurement of refractive index fluctuations inside a flame volume is demonstrated.
Application of GPU-based, highly parallelized algorithms for the estimation of electromagnetic multi-layer interactions
Show abstract
In nowadays industry, complex surfaces with material contrasts or surface coatings are present and represent a challenge
for optical topography measuring instruments. The reason is that varying optical properties lead to phase jumps and to
topography deviations when the surface height is evaluated. Thus, Ellipso-Height-Topometry as a measurement
technique which can measure both topography and material properties of technical surfaces was proposed in order to
achieve a correction of the occurring topographic artefacts. The height correction value can be obtained for the
compensation of material-induced height deviations and the thickness of surface layers can be evaluated. Currently, it is
possible to calculate the surface characteristics from ellipsometric parameters for at most two layers. However, the
described height corrections are only possible when well-defined and realistic models of surface layers can be utilized,
e.g. a given set of homogeneous oxide layers. Oxidation effects however describe statistical processes which can be
predicted with underlying material distribution models. This leads to an uncertainty in ellipsometry, which is considered
with a new approach that will be discussed in this publication. Therefore, an extended multi-layer approach which is
capable of handling additional layers based on a parallelized algorithm using graphic processing units and the commonly
known CUDA technology is proposed. This algorithm can also be used to consider material proportions which result
from oxidation effects in z direction. The new approach for the Ellipso-Height-topometry measurement technique is
compared with the current procedures which often neglect the existence of an oxide layer for the basic material. To
experimentally verify the approach and according algorithm, it is applied for the evaluation of actual surfaces with
multiple plane layers and different materials. Test samples with different materials are used in order to evaluate the
complex refractive index, the distribution of identified materials and the layer thicknesses with actual Ellipso-Height-
Topometry measurements. The results of the measurements are compared to the predicted theoretical results.
In-situ and Nondestructive Testing III
3D interferometric shape measurement technique using coherent fiber bundles
Show abstract
In-situ 3-D shape measurements with submicron shape uncertainty of fast rotating objects in a cutting lathe are expected, which can be achieved by simultaneous distance and velocity measurements. Conventional tactile methods, coordinate measurement machines, only support ex-situ measurements. Optical measurement techniques such as triangulation and conoscopic holography offer only the distance, so that the absolute diameter cannot be retrieved directly. In comparison, laser Doppler distance sensors (P-LDD sensor) enable simultaneous and in-situ distance and velocity measurements for monitoring the cutting process in a lathe. In order to achieve shape measurement uncertainties below 1 μm, a P-LDD sensor with a dual camera based scattered light detection has been investigated. Coherent fiber bundles (CFB) are employed to forward the scattered light towards cameras. This enables a compact and passive sensor head in the future. Compared with a photo detector based sensor, the dual camera based sensor allows to decrease the measurement uncertainty by the order of one magnitude. As a result, the total shape uncertainty of absolute 3-D shape measurements can be reduced to about 100 nm.
Interferometric fibre-optic curvature sensing for structural, directional vibration measurements
Show abstract
Dynamic fibre-optic curvature sensing using fibre segment interferometry is demonstrated using a cost-effective rangeresolved
interferometry interrogation system. Differential strain measurements from four fibre strings, each containing
four fibre segments of gauge length 20 cm, allow the inference of lateral vibrations as well as the direction of the
vibration of a cantilever test object. Dynamic tip displacement resolutions in the micrometre range over a 21 kHz
interferometric bandwidth demonstrate the suitability of this approach for highly sensitive fibre-optic directional
vibration measurements, complementing existing laser vibrometry techniques by removing the need for side access to the
structure under test.
Subpixel edge estimation with lens aberrations compensation based on the iterative image approximation for high-precision thermal expansion measurements of solids
Show abstract
A new method for precise subpixel edge estimation is presented. The principle of the method is the iterative image
approximation in 2D with subpixel accuracy until the appropriate simulated is found, matching the simulated and
acquired images. A numerical image model is presented consisting of three parts: an edge model, object and background
brightness distribution model, lens aberrations model including diffraction. The optimal values of model parameters are
determined by means of conjugate-gradient numerical optimization of a merit function corresponding to the L2 distance
between acquired and simulated images. Computationally-effective procedure for the merit function calculation along
with sufficient gradient approximation is described. Subpixel-accuracy image simulation is performed in a Fourier
domain with theoretically unlimited precision of edge points location. The method is capable of compensating lens
aberrations and obtaining the edge information with increased resolution. Experimental method verification with digital
micromirror device applied to physically simulate an object with known edge geometry is shown. Experimental results
for various high-temperature materials within the temperature range of 1000°C..2400°C are presented.
Posters--Tuesday
New technique for generating light source array in tilted wave interferometer
Show abstract
Smaller and lighter optical systems with better performance can be built by the use of freeform optics.
However, most optical systems were constrained to traditional surfaces for the accurate metrology of
freeform surface is a challenge so far unsolved. One high-precision approach to measure freeform
surface with less time and expense is using tilted wave interferometer. A lens array is placed in the test
path of the interferometer, which can generate light source array that locally compensate the gradient of
test surface. But each source generated by lens array is not ideal spherical wave which contains
aberrations. In addition, the sources cannot be activated individually during the measurement, so that it
is impossible to perform an irregular source array according to the gradient variation of each test
surface. Thus, a novel technique based on fiber array is proposed for generating irregular source array.
Whereas, the position deviation of each fiber and phase difference produced by the length of each fiber
affect the measurement result. In this paper, the consequences of above errors are analyzed. A
calibration method can obtain the exact spatial coordinates of each fiber is suggested to calculate the
position deviation of each fiber. Meanwhile, a method based on Mach-Zehnder interference system is
presented, which can get phase difference produced by the length of each fiber accurately. Afterwards,
the data obtained by the two calibration methods are introduced into the mathematical model of system
error for eliminating the measurement error introduced by the use of fiber array. An elliptical mirror is
measured by our tilted wave interferometer based on fiber array showing the feasibility of the proposed
methods.
Absolute test using the conjugate differential method
Show abstract
The conjugate differential method has been applied to the absolute test of flat, cylindrical, and axicon surfaces. In the
previous work, simulations and correspond experiments have been carried out to verify the feasibility of the method. To
analyze the influences of different factors upon the measurement result, the conjugate differential method is discussed in
detail. Considering the characteristics of the test surface such as surface types and surface profiles, the application ranges
of the conjugate differential method are discussed into three parts. According to the three surface types using the
conjugate differential method, the method can be extended to the absolute test of the spherical surfaces based on
spherical coordinate system. The reconstructed errors caused by different aberrations expressed as Zernike polynomial
terms show that they are more sensitive to high order aberration terms of the surface under test. And for surfaces with
different frequency distributions, the surface with less mid-spatial frequency information is less sensitive to the sampling
frequency. The influence from the other factors in interferometric test are also discussed into three parts. The influences
from the uncertainty of shifts are correlated with the increased aperture diameters, since the integration error caused by
the shift error increases gradually with the expanding of the integration path. The integration error changes by the
influences from the coherent noise and pixel noise related to pixel deviations. The reconstructed deviations get increased
while the peak pixel deviation is increasing. For the balance of the differential deviation and integration error, the
optimization of sampling resolution should take considered for accuracy improvement.
Optical scanner system for high resolution measurement of lubricant distributions on metal strips based on laser induced fluorescence
Show abstract
We present a new optical setup, which uses scanning mirrors in combination with laser induced fluorescence to monitor
the spatial distribution of lubricant on metal sheets.
Current trends in metal processing industry require forming procedures with increasing deformations. Thus a welldefined amount of lubricant is necessary to prevent the material from rupture, to reduce the wearing of the manufacturing tool as well as to prevent problems in post-deforming procedures. Therefore spatial resolved analysis of the thickness of lubricant layers is required. Current systems capture the lubricant distribution by moving sensor heads over the object along a linear axis. However the spatial resolution of these systems is insufficient at high strip speeds, e.g. at press plants.
The presented technology uses fast rotating scanner mirrors to deflect a laser beam on the surface. This 405 nm laser light excites the autofluorescence of the investigated lubricants. A coaxial optic collects the fluorescence signal which is then spectrally filtered and recorded using a photomultiplier. From the acquired signal a two dimensional image is reconstructed in real time. This paper presents the sensor setup as well as its characterization. For the calibration of the system reference targets were prepared using an ink jet printer.
The presented technology for the first time allows a spatial resolution in the millimetre range at production speed. The presented test system analyses an area of 300 x 300 mm² at a spatial resolution of 1.1 mm in less than 20 seconds. Despite this high speed of the measurement the limit of detection of the system described in this paper is better than 0.05 g/m² for the certified lubricant BAM K-009.
Current trends in metal processing industry require forming procedures with increasing deformations. Thus a welldefined amount of lubricant is necessary to prevent the material from rupture, to reduce the wearing of the manufacturing tool as well as to prevent problems in post-deforming procedures. Therefore spatial resolved analysis of the thickness of lubricant layers is required. Current systems capture the lubricant distribution by moving sensor heads over the object along a linear axis. However the spatial resolution of these systems is insufficient at high strip speeds, e.g. at press plants.
The presented technology uses fast rotating scanner mirrors to deflect a laser beam on the surface. This 405 nm laser light excites the autofluorescence of the investigated lubricants. A coaxial optic collects the fluorescence signal which is then spectrally filtered and recorded using a photomultiplier. From the acquired signal a two dimensional image is reconstructed in real time. This paper presents the sensor setup as well as its characterization. For the calibration of the system reference targets were prepared using an ink jet printer.
The presented technology for the first time allows a spatial resolution in the millimetre range at production speed. The presented test system analyses an area of 300 x 300 mm² at a spatial resolution of 1.1 mm in less than 20 seconds. Despite this high speed of the measurement the limit of detection of the system described in this paper is better than 0.05 g/m² for the certified lubricant BAM K-009.
Characterizing the quality of the fiber optic reference for cylindrical wave testing
Show abstract
With continued advances in cylindrical optics manufacturing capability, interferometric testing of such optics is difficult.
This is due to the lack of a well characterized cylindrical reference surface. In this paper, the Random Fiber Test (RFT)
is used to experimentally quantify the quality of fiber surface as a cylindrical reference. The basic idea of the experiment
is to take measurements at different rotations about, and translations along the fiber axis. From these measurements the
quality of the fiber surface in both directions can be determined.
Analysis of the fractures of metallic materials using optical coherence tomography
Show abstract
Forensic in situ investigations, for example for aviation, maritime, road, or rail accidents would benefit from a method
that may allow to distinguish ductile from brittle fractures of metals - as material defects are one of the potential causes
of such accidents. Currently, the gold standard in material studies is represented by scanning electron microscopy
(SEM). However, SEM are large, lab-based systems, therefore in situ measurements are excluded. In addition, they are
expensive and time-consuming. We have approached this problem and propose the use of Optical Coherence
Tomography (OCT) in such investigations in order to overcome these disadvantages of SEM. In this respect, we
demonstrate the capability to perform such fracture analysis by obtaining the topography of metallic surfaces using OCT.
Different materials have been analyzed; in this presentation a sample of low soft carbon steel with the chemical
composition of C 0.2%, Mn 1.15%, S 0.04%, P 0.05 % and Fe for the rest has been considered. An in-house developed
Swept Source (SS) OCT system has been used, and height profiles have been generated for the sample surface. This
profile allowed for concluding that the carbon steel sample was subjected to a ductile fracture. A validation of the OCT
images obtained with a 10 microns resolution has been made with SEM images obtained with a 4 nm resolution.
Although the OCT resolution is much lower than the one of SEM, we thus demonstrate that it is sufficient in order to
obtain clear images of the grains of the metallic materials and thus to distinguish between ductile and brittle fractures.
This study analysis opens avenues for a range of applications, including: (i) to determine the causes that have generated
pipe ruptures, or structural failures of metallic bridges and buildings, as well as damages of machinery parts; (ii) to
optimize the design of various machinery; (iii) to obtain data regarding the structure of metallic alloys); (iv) to improve
the manufacturing technologies of metallic parts.
A novel white-light interferometry using low differential-frequency heterodyne system
Show abstract
The optical surface profiler offers fast non-contact and high-precision 3D metrology for complex surface features, which
are widely used in the field of precision machining manufacturing. The optical surface profiler traditionally adopts the
white light interference (WLI) technique which mainly includes optical interference system and high-precision
displacement stage. The accuracy of the displacement table determines the longitudinal resolution of the instrument. In
this paper, a novel WLI technique is proposed, i.e. full-field heterodyne WLI, which combines common displacement
stage, low differential-frequency heterodyne system and optical interferometry system. The low differential-frequency
heterodyne system generates heterodyne signal in the range of laser coherence length. By using the digital phase shift in
substitution for the mechanical phase shift, the vertical resolution increases from the sub-nanometer level to the
sub-angstrom level. Due to the low difference frequency technique, the common area array detector acquisition is
available. A fixed displacement stage position obtains a set of three-dimensional data cubes. Through Fourier-Transform
process of the time series data, the initial phase of each pixel at a specific heterodyne frequency is calculated and
transformed into surface height information. By using phase unwrapping, the object surface profile can be restored
within the laser coherence length. Through digital phase-shifting, phase extraction technology replaces the intensity
extraction technology, the moving distance of the displacement can be calibrated with high precision. Thus it can achieve
a large range of high-precision contour measurement and reduce the cost of the instrument.
Fiber Bragg gratings strain measuring system and a sensor calibration setup based on mechanical nanomotion transducer
Show abstract
Fiber Bragg grating (FBG) strain sensors are powerful tools for structural health monitoring applications. However, FBG sensor fabrication and packaging processes can lead to a non-linear behavior, that affects the accuracy of the strain measurements. Here we present a novel nondestructive calibration technique for FBG strain sensors that use a mechanical nanomotion transducer. A customized calibration setup was designed based on dovetail-type slideways that were mechanized using a stepping motor. The performance of the FBG strain sensor was investigated through analysis of experimental data, and the calibration curves for the FBG strain sensor are presented.
Evaluation and tolerancing of irregularly shaped interferometric test regions
Show abstract
The evaluation of non-circular test regions poses an unusual but tricky problem to interferometric testing since typical
polynomial decompositions of the measured wavefront like Zernikes are only valid in a circular region. Despite the fact
that of course non-circular polynomial decompositions exist they still rely on regular regions like ellipses or rectangles.
For irregular shapes of test regions no widely accepted general decomposition exists.
Unfortunately it is necessary in some cases to test completely irregularly shaped test regions. May it because the optics simply is of this shape and needs to be tested in this state or because the used area is irregular and it is undesired to extend the test region to a larger, but regular shape.
We present a simple method that not only provides a possibility to evaluate any arbitrary shaped test region but also to have a tolerance model that gives reasonable and uses worldwide accepted specification standards.
Certain interferometer software may be suited for an appropriate data analysis. An overview over some commercially available interferometer software is given with respect to the requirement of the presented method.
Unfortunately it is necessary in some cases to test completely irregularly shaped test regions. May it because the optics simply is of this shape and needs to be tested in this state or because the used area is irregular and it is undesired to extend the test region to a larger, but regular shape.
We present a simple method that not only provides a possibility to evaluate any arbitrary shaped test region but also to have a tolerance model that gives reasonable and uses worldwide accepted specification standards.
Certain interferometer software may be suited for an appropriate data analysis. An overview over some commercially available interferometer software is given with respect to the requirement of the presented method.
Remote sensing of atmospheric turbulence profiles by laser guide stars
Show abstract
Remote sensing of ranged-resolved profiles of atmospheric turbulence is necessary and important for many applications in
astronomical and adaptive optics communities. In order to obtain turbulence profiles in atmospheric boundary layer, a
device is developed and experiments has been carried out. In the experiments, laser guide stars are formed at several
successive altitudes by projecting pulsed laser, returned signals are received by two receiving telescopes and the images of
the returned signals are formed by a imaging device. Variance of centroids′ distance is derived from the images with two
spots at the same altitude and ranged-resolved profile of the variance is obtained. So, based on a inversion algorithm,
atmospheric turbulence profiles are retrieved from differential image motion variance of distance of centroids at various
altitudes. The structure constants of refractive index of atmosphere range from 10-14m-2/3 at lower altitudes to 10-16m-2/3 at
higher altitudes are remote sensed experimentally. The results show it is a effective method that combined laser guide stars
with differential image motion method and could sense atmospheric turbulence profiles remotely in real time.
Laser-line scanning speckle reduction based on a one-dimensional beam homogenizer
Show abstract
Laser-line scanners have become ubiquitous in many forms of automation and measurement systems. Despite this fact, these systems are still susceptible to speckle or interference on rough scattering surfaces. Many scanning systems must be calibrated to the material being analyzed to obtain their full potential. In general, post-processing algorithms are used in most modern line-scanning devices in order to smooth out speckle and enhance the resolution through sub-pixel interpolation. However, these post-processing techniques come at a cost of increased CPU time and a subsequent decrease in bandwidth and resolution. in this paper, a low-cost, high-resolution solution to generating speckle-free sharply focused laser lines is presented. The key to this technique relies on only removing the spatial coherence in one dimension using a 1-D cylindrical lens array as a beam homogenizer. This beam homogenizer is then wrapped around and rotated about a central axis in order to remove the temporal component on the laser's coherence. Since the plane-wave-like behavior is maintained along one dimension, this beam can still be sharply focused to a line. however, the spatial coherence and temporal coherence are reduced to the point that speckle is minimally visible.
High-power LED light sources for optical measurement systems operated in continuous and overdriven pulsed modes
Show abstract
The rapid progress of light emitting diode (LED) technology has recently resulted in the availability of high power
devices with unprecedented light emission intensities comparable to those of visible laser light sources. On this basis two
versatile devices have been developed, constructed and tested.
The first one is a high-power, single-LED illuminator equipped with exchangeable projection lenses providing a homogenous light spot of defined diameter. The second device is a multi-LED illuminator array consisting of a number of high-power LEDs, each integrated with a separate collimating lens. These devices can emit R, G, CG, B, UV or white light and can be operated in pulsed or continuous wave (CW) mode. Using an external trigger signal they can be easily synchronized with cameras or other devices. The mode of operation and all parameters can be controlled by software. Various experiments have shown that these devices have become a versatile and competitive alternative to laser and xenon lamp based light sources.
The principle, design, achieved performances and application examples are given in this paper.
The first one is a high-power, single-LED illuminator equipped with exchangeable projection lenses providing a homogenous light spot of defined diameter. The second device is a multi-LED illuminator array consisting of a number of high-power LEDs, each integrated with a separate collimating lens. These devices can emit R, G, CG, B, UV or white light and can be operated in pulsed or continuous wave (CW) mode. Using an external trigger signal they can be easily synchronized with cameras or other devices. The mode of operation and all parameters can be controlled by software. Various experiments have shown that these devices have become a versatile and competitive alternative to laser and xenon lamp based light sources.
The principle, design, achieved performances and application examples are given in this paper.
The research of structured reflective surface of matrix sensor according to generalized scheme of ellipsometry
Show abstract
The work is devoted to ellipsometric investigation of the structured reflecting surface of a matrix sensor. By the
generalized scheme of ellipsometry, the optical and geometric parameters of the layers of the matrix receiver can be
determined. These parameters include the thickness and refractive index. Ellipsometric angles were determined using
the ellipsometer. They are used as input data in the inverse ellipsometry problem. After determining the thickness and
refractive indices of the sensor layers, it is possible to calculate its transmittance.When this indicator is known ,the
sensitivity of the receiver can be calculated at the certain point. In this work the algorithm of the calculation of the
sensitivity of a matrix receiver of optical radiation is described ,the input data in this algorithm are considered to be the
ellipsometric angles.
Phase A: calibration concepts for HIRES
Show abstract
The instrumentation plan for the E-ELT foresees a High Resolution Spectrograph (HIRES). Among its main goals are the detection of atmospheres of exoplanets and the determination of fundamental physical constants. For this, high radial velocity precision and accuracy are required. HIRES will be designed for maximum intrinsic stability. Systematic errors from effects like intrapixel variations or random errors like fiber noise need to be calibrated. Based on the main requirements for the calibration of HIRES, we discuss different potential calibration sources and how they can be applied. We outline the frequency calibration concept for HIRES using these sources.
Development of hydrogen sensors based on fiber Bragg grating with a palladium foil for online dissolved gas analysis in transformers
Show abstract
Hydrogen evolution, identified by dissolved gas analysis (DGA), is commonly used for fault detection in oil immersed
electrical power equipment. Palladium (Pd) is often used as a sensing material due to its high hydrogen absorption
capacity and related change in physical properties. Hydrogen is absorbed by Pd causing an expansion of the lattice. The
solubility, and therefore lattice expansion, increases with increasing partial pressure of hydrogen and decreasing
temperature. As long as a phase change is avoided the expansion is reversible and can be utilized to transfer strain into a
sensing element. Fiber Bragg gratings (FBG) are a well-established optical fiber sensor (OFS), mainly used for
temperature and strain sensing. A safe, inexpensive, reliable and precise hydrogen sensor can be constructed using an
FBG strain sensor to transduce the volumetric expansion of Pd due to hydrogen absorption.
This paper reports on the development, and evaluation, of an FBG gas sensing OFS and long term measurements of
dissolved hydrogen in transformer mineral oil. We investigate the effects of Pd foil cross-section and strain transfer
between foil and fiber on the sensitivity of the OFS. Two types of Pd metal sensors were manufactured using modified
Pd foil with 20 and 100 μm thickness. The sensors were tested in transformer oil at 90°C and a hydrogen concentration
range from 20- 3200 ppm.
Development of a low-cost, 11 µm spectral domain optical coherence tomography surface profilometry prototype
Show abstract
A spectral-domain Optical Coherence Tomography (OCT) surface profilometry prototype has been developed for the
purpose of surface metrology of optical elements. The prototype consists of a light source, spectral interferometer,
sample fixture and software currently running on Microsoft® Windows platforms. In this system, a broadband light
emitting diode beam is focused into a Michelson interferometer with a plane mirror as its sample fixture. At the
interferometer output, spectral interferograms of broadband sources were measured using a Czerny-Turner mount
monochromator with a 2048-element complementary metal oxide semiconductor linear array as the detector. The
software performs importation and interpolation of interferometer spectra to pre-condition the data for image
computation. One dimensional axial OCT images were computed by Fourier transformation of the measured spectra. A
first reflection surface profilometry (FRSP) algorithm was then formulated to perform imaging of step-function-surfaced
samples. The algorithm re-constructs two dimensional colour-scaled slice images by concatenation of 21 and 13 axial
scans to form a 10 mm and 3.0 mm slice respectively. Measured spectral interferograms, computed interference fringe
signals and depth reflectivity profiles were comparable to simulations and correlated to displacements of a single
reflector linearly translated about the arm null-mismatch point. Surface profile images of a double-step-function-surfaced
sample, embedded with inclination and crack detail were plotted with an axial resolution of 11 μm. The surface shape,
defects and misalignment relative to the incident beam were detected to the order of a micron, confirming high resolution
of the developed system as compared to electro-mechanical surface profilometry techniques.
Gas monitoring onboard ISS using FTIR spectroscopy
Show abstract
In the confined, enclosed environment of a spacecraft, the air quality must be monitored continuously in order to
safeguard the crew's health. For this reason, OHB builds the ANITA2 (Analysing Interferometer for Ambient Air)
technology demonstrator for trace gas monitoring onboard the International Space Station (ISS). The measurement
principle of ANITA2 is based on the Fourier Transform Infrared (FTIR) technology with dedicated gas analysis software
from the Norwegian partner SINTEF. This combination proved to provide high sensitivity, accuracy and precision for
parallel measurements of 33 trace gases simultaneously onboard ISS by the precursor instrument ANITA1.
The paper gives a technical overview about the opto-mechanical components of ANITA2, such as the interferometer, the
reference Laser, the infrared source and the gas cell design and a quick overview about the gas analysis.
ANITA2 is very well suited for measuring gas concentrations specifically but not limited to usage onboard spacecraft, as
no consumables are required and measurements are performed autonomously.
ANITA2 is a programme under the contract of the European Space Agency, and the air quality monitoring system is a
stepping stone into the future, as a precursor system for manned exploration missions.
Experimental light scattering by small particles: system design and calibration
Show abstract
We describe a setup for precise multi-angular measurements of light scattered by mm- to μm-sized samples. We present
a calibration procedure that ensures accurate measurements. Calibration is done using a spherical sample (d = 5 mm, n =
1.517) fixed on a static holder. The ultimate goal of the project is to allow accurate multi-wavelength measurements (the
full Mueller matrix) of single-particle samples which are levitated ultrasonically.
The system comprises a tunable multimode Argon-krypton laser, with 12 wavelengths ranging from 465 to 676 nm, a linear polarizer, a reference photomultiplier tube (PMT) monitoring beam intensity, and several PMT:s mounted radially towards the sample at an adjustable radius. The current 150 mm radius allows measuring all azimuthal angles except for ±4° around the backward scattering direction. The measurement angle is controlled by a motor-driven rotational stage with an accuracy of 15’.
The system comprises a tunable multimode Argon-krypton laser, with 12 wavelengths ranging from 465 to 676 nm, a linear polarizer, a reference photomultiplier tube (PMT) monitoring beam intensity, and several PMT:s mounted radially towards the sample at an adjustable radius. The current 150 mm radius allows measuring all azimuthal angles except for ±4° around the backward scattering direction. The measurement angle is controlled by a motor-driven rotational stage with an accuracy of 15’.
Light section measurement to quantify the accuracy loss induced by laser light deflection in an inhomogeneous refractive index field
Show abstract
In the manufacturing process of Tailored Forming components, the inline inspection of the joining zone directly after each single process step can yield advantages - such as early error detection and real-time process control. Since measuring times need to be synchronized with the production chain, there is no time to cool down the components in between two hot forming processes. On the one hand, the chosen measurement technique needs to be non-tactile due to the heat of the measurement object. On the other hand, the object's areal surface texture needs to be captured rapidly to realize a fast inline inspection. These requirements are only matched by optical 3d measurement systems. Additional challenges arise due to the high temperature of the Tailored Forming components: the ambient air is heated up and the air's temperature increase results in an inhomogeneous refractive index field surrounding the hot workpiece, effecting the light's path emitted by the illumination unit of the optical sensor. We present a simple measurement setup based on the laser light section method to visualize the measurement accuracy loss induced by the convectional heat flow from a hot cylindrical measurement object. To attain a direct validation of the measurement results, the measurements are performed with and with reduced influence of the inhomogeneous refractive index field induced by the hot object.
Digital holographic inspection for drying processes of paint films and ink dots
Show abstract
Digital holographic techniques to investigate drying processes of both paint films and ink dot is presented. The proposed
technique based on digital holographic interferometry can achieve both visualization of variations and analysis of
dryness of paint films in the drying process by using phase changes between two subsequent reconstructed complex
amplitudes of the reflected light from the film. To follow the drying processes, holograms are recorded at a constant time
interval. Phase-shifting digital holography has been applied to analyze the dryness of commercial paints applied on the
metal plate. For analysis of an ink dot having diameter of a few hundred micrometers, digital holographic microscopy is
applied to evaluating the time history of dryness of ink dot in the drying process. This paper describes these holographic
techniques applied to the commercially available paint and ink and presents some experimental results.
Development of optical-electronic autocollimation sensor for industrial inspection with an increased measurement range
Show abstract
The construction features of autocollimation systems for measurement the large-sized and extended objects deformations
at industry, power and scientific instrument making are considered. The conditions of increase of a distance of
measurement are analyzed in comparison with the serial autocollimation devices. The error of measurement by the
restriction of a working beam is investigated. The structure of algorithm for reduces the systematic error of the
measurement which based on received analytical expression of function of an error is determined.
Influence of the limited detector size on spatial variations of the reconstruction accuracy in holographic tomography
Show abstract
Holographic tomography (HT) allows noninvasive, quantitative, 3D imaging of transparent microobjects, such as living
biological cells and fiber optics elements. The technique is based on acquisition of multiple scattered fields for various
sample perspectives using digital holographic microscopy. Then, the captured data is processed with one of the
tomographic reconstruction algorithms, which enables 3D reconstruction of refractive index distribution.
In our recent works we addressed the issue of spatially variant accuracy of the HT reconstructions, which results from the insufficient model of diffraction that is applied in the widely-used tomographic reconstruction algorithms basing on the Rytov approximation. In the present study, we continue investigating the spatially variant properties of the HT imaging, however, we are now focusing on the limited spatial size of holograms as a source of this problem. Using the Wigner distribution representation and the Ewald sphere approach, we show that the limited size of the holograms results in a decreased quality of tomographic imaging in off-center regions of the HT reconstructions. This is because the finite detector extent becomes a limiting aperture that prohibits acquisition of full information about diffracted fields coming from the out-of-focus structures of a sample. The incompleteness of the data results in an effective truncation of the tomographic transfer function for the out-of-center regions of the tomographic image. In this paper, the described effect is quantitatively characterized for three types of the tomographic systems: the configuration with 1) object rotation, 2) scanning of the illumination direction, 3) the hybrid HT solution combing both previous approaches.
In our recent works we addressed the issue of spatially variant accuracy of the HT reconstructions, which results from the insufficient model of diffraction that is applied in the widely-used tomographic reconstruction algorithms basing on the Rytov approximation. In the present study, we continue investigating the spatially variant properties of the HT imaging, however, we are now focusing on the limited spatial size of holograms as a source of this problem. Using the Wigner distribution representation and the Ewald sphere approach, we show that the limited size of the holograms results in a decreased quality of tomographic imaging in off-center regions of the HT reconstructions. This is because the finite detector extent becomes a limiting aperture that prohibits acquisition of full information about diffracted fields coming from the out-of-focus structures of a sample. The incompleteness of the data results in an effective truncation of the tomographic transfer function for the out-of-center regions of the tomographic image. In this paper, the described effect is quantitatively characterized for three types of the tomographic systems: the configuration with 1) object rotation, 2) scanning of the illumination direction, 3) the hybrid HT solution combing both previous approaches.
New method for probe position correction for Ptychography
Show abstract
For high resolution imaging, X-rays and electron beams are being used. However, for such a short wavelength, imaging with lenses becomes difficult as lenses absorb a part of radiation and lenses with very low aberrations must be used. Ptychography is a lens-less imaging technique which uses intensity information of the multiple diffraction patterns in the far field. These multiple far field diffraction patterns are generated by an unknown object which is scanned by a localized illuminated spot (probe).
Accurate knowledge of initial parameters is important for a good reconstruction of the object. Robustness of the Ptychography Iterative Engine (PIE) has already been studied for inaccurately known initial parameters, where the success of the algorithm was found to be sensitive to the accuracy of the estimate of lateral positions of the probe.
:; We present here a new method to correct the lateral position of the probe with respect to the object. This method is more straightforward to implement than other existing algorithms while comparable accuracy for the lateral position is achieved. Being able to correct the probe positions has positive implication in experiments, in particular at the short wavelength cases. It relaxes the requirement for the experimental set-up.
Accurate knowledge of initial parameters is important for a good reconstruction of the object. Robustness of the Ptychography Iterative Engine (PIE) has already been studied for inaccurately known initial parameters, where the success of the algorithm was found to be sensitive to the accuracy of the estimate of lateral positions of the probe.
:; We present here a new method to correct the lateral position of the probe with respect to the object. This method is more straightforward to implement than other existing algorithms while comparable accuracy for the lateral position is achieved. Being able to correct the probe positions has positive implication in experiments, in particular at the short wavelength cases. It relaxes the requirement for the experimental set-up.
Holographic prism based on photo-thermo-refractive glass
Show abstract
New application of photo-thermo-refractive glass (PTR) named “holographic prism” is presented. In the
holographic prism angles between directions are set by the holograms which create “fan” of signal beams. This kind of
prism creates several signal beams which are equal to the reflections from facets of the conventional silica prism.
Implementation of PTR glass as a holographic medium for this device brought us several advantages and new features.
First it leads to decrease in overall size of the prism that positively affects the identification process of the beam's crosspoint.
Thus, it increases sensitivity and accuracy of the measure. Second, greater value of the refractive index change in
PTR glass in comparison with calcium fluoride crystal allows us to increase quantity of the recorded reference beams for
the measure which leads to sensitivity increase. During this work, we established recording schedule for the PTR glass in
case of the superimposed gratings recording. Was found that exposure for each grating should be equal to the 1/N fraction
of the optimal exposure where N is the number of multiplexed gratings. We proved that in this case the total value of the
refractive index modulation amplitude is equal to that for the single grating with optimal exposure. Considering obtained
data we successfully performed recording of the holographic prism of the second modification with 14 channels.
Component-level test of molded freeform optics for LED beam shaping using experimental ray tracing
Show abstract
Due to the high demand of LED light sources, the need to modify their radiation pattern to meet specific application
requirements has also increased. This is mostly achieved by using molded secondary optics, which are composed of a
combination of several aspherical and freeform surfaces. Unfortunately, the manufacturers of these secondary optics only
provide output information at system level, making impossible to independently characterize the secondary optic in order
to determine the sources of erroneous results. For this reason, it is necessary to perform a component-level verification
leading to the validation of the correctness of the produced secondary optic independently of the light source. To
understand why traditional inspection methods fail, it is necessary to take into account that not only errors due to
irregularities on the lens surface like pores, glass indentations or scratches affect the performance of the lens, but also
differences in refractive index appear after the compression during fabrication process. These internal alterations are
generally produced during the cooling stage and their effect over the performance of the lens are not possible to be
measured using tactile techniques. Additionally, the small size of the lens and the freeform characteristics of its surface
introduce additional difficulties to perform its validation. In this work, the component-level test is done by obtaining the
ray mapping function (RMF) which describes the deflection of the light beam as a function of the input angle. To obtain
the RMF, firstly a collimated light source is held fix and the lens is rotated. Thus, a virtual point source is created and
subsequently by using experimental ray tracing it is possible to determine the ray slopes, which are used to the retrieve
the RMF. Under the assumption that the optical system under analysis is lossless and considering the principle of energy
conservation, it is possible under specific conditions to use this new approach to obtain the output of the complete set,
composed of light source plus secondary optic. Thus, for different LED models, combining their radiation pattern with
the RMF allow us to obtain the resultant modified radiation pattern. By following this procedure, the correct
functionality of the secondary optic is verified independently of the light source. This method brings the opportunity to
the final product manufacturer of defining fail regions over the desired resultant output radiation pattern as a
combination of different LED sources and then verify if the secondary optic fulfill the requirements.
Characterization of edge effects in precision low-coherence interferometry using broadband light sources
Show abstract
Within this work an alternative approach to precision surface profilometry based on a low-coherence interferometer is presented. Special emphasis is placed on the characterization of edge effects, which influence the measurement result on sharp edges and steep slopes. In contrast to other works, this examination focuses on the comparison of very broadband light sources such as a supercontinuum white-light source (SC; 380 - 1100 nm) and a laser-driven plasma light source (LDP; 200 - 1100 nm) and their influence on the formation of these effects. The interferometer is equipped with one of these broadband light sources and a defined dispersion over a given spectral range. The spectral width of the light sources in combination with the dispersive element defines the possible measurement range and resolution. Instead of detecting the signals only in a one-dimensional manner, an imaging spectrometer on the basis of a high resolution CMOS-camera is set-up. Through the introduction of a defined dispersion, a controlled phase variation in the spectral domain is created. This phase variation is dependent on the optical path difference between both arms and can therefore be used as a measure for the height of a structure which is present in one arm.
The results of measurements on a 100 nm height standard with both selected light sources have been compared. Under consideration of the coherence length of both light sources of 1.58 μm for the SC source and 1.81 m for the LDP source differences could be recorded. Especially at sharp edges, the LDP light source could record height changes with slopes twice as steep as the SC source. Furthermore, it became obvious, that measurements with the SC source tend to show edge effects like batwings due to diffraction. Additional effects on the measured roughness and the flatness of the profile were investigated and discussed.
The results of measurements on a 100 nm height standard with both selected light sources have been compared. Under consideration of the coherence length of both light sources of 1.58 μm for the SC source and 1.81 m for the LDP source differences could be recorded. Especially at sharp edges, the LDP light source could record height changes with slopes twice as steep as the SC source. Furthermore, it became obvious, that measurements with the SC source tend to show edge effects like batwings due to diffraction. Additional effects on the measured roughness and the flatness of the profile were investigated and discussed.
In-line height profiling metrology sensor for zero defect production control
Show abstract
Contemporary production systems of mechanical precision parts show challenges as increased complexity, tolerances
shrinking to sub-microns and yield losses that must be mastered to the extreme. More advanced automation and process
control is required to accomplish this task. Often a solution based on feedforward/feedback control is chosen requiring
innovative and more advanced in line metrology. This article concentrates first on the context of in line metrology for
process control and then on the development of a specific in line height profiling sensor. The novel sensor technology is
based on full field time domain white light interferometry which is well know from the quality lab. The novel metrology
system is to be mounted close to the production equipment, as required to minimize time delay in the control loop, and is
thereby fully exposed to vibrations. This sensor is innovated to perform in line with an orders of magnitude faster
throughput than laboratory instruments; it’s robust to withstand the rigors of workshops and has a height resolution that
is in the nanometer range.
Compact DPSS-laser source for LIBS analysis of steel
Show abstract
LIBS-technology holds the potential for on-site real-time measurements of steel products. However for a mobile and
robust LIBS measurement system, an adequate small and ruggedized laser source is a key-requirement. In this
contribution, we present tests with our novel compact high power laser source, which, initially, was developed for
ignition applications. The CTR HiPoLas® laser is a robust diode pumped solid state laser with a passive Q-switch with
dimensions of less than 10 cm³. The laser generates 2.5 ns-pulses with 30 mJ at a maximum continuous repetition rate of
about 30 Hz. Feasibility of LIBS experiments with the laser source was experimentally verified with steel samples. The
results show that the laser with its current optical output parameters is very well suited for LIBS measurements. We
believe that the miniaturized laser presented here will enable very compact and robust portable high-performance LIBS
systems.
Design and fabrication of micro silica sphere cavity force sensor based on hybrid Fabry Perot interferometer
Show abstract
Measurement of small force in biological applications could be helpful especially in the field of diagnostic and
prognostic procedure. For this purpose, a Hybrid Fabry Perot fiber optic Micro Cavity is proposed based on Micro Silica
Sphere Cavity integrated on the capillary tube, and is bound to the single mode fiber with PDMS layer. Since PDMS acts
as an elastic material, under small loads the cavity length was affected. To study this mechanical behavior, the sensor
structure was simulated with Finite element method. The force measurement was studied experimentally with analyzing
wavelength shifts of sensor. Consequently, the force sensitivity was equal to -3pm/mN. The force resolution of our
sensor was equal to 340 μN in the range of 0 to 950 mN.
Fast searching measurement of absolute displacement based on submicron-aperture fiber point-diffraction interferometer
Show abstract
The submicron-aperture fiber point-diffraction interferometer (SFPDI) can be applied to realize the measurement of
three-dimensional absolute displacement within large range, in which the performance of point-diffraction wavefront and
numerical iterative algorithm for displacement reconstruction determines the achievable measurement accuracy,
reliability and efficiency of the system. A method based on fast searching particle swarm optimization (FS-PSO)
algorithm is proposed to realize the rapid measurement of three-dimensional absolute displacement. Based on the SFPDI
with two submicron-aperture fiber pairs, FS-PSO method and the corresponding model of the SFPDI, the measurement
accuracy, reliability and efficiency of the SFPDI system are significantly improved, making it more feasible for practical
application. The effect of point-diffraction wavefront error on the measurement is analyzed. The error of pointdiffraction
wavefront obtained in the experiment is in the order of 1×10-4λ (the wavelength λ is 532 nm), and the
corresponding displacement measurement error is smaller than 0.03 μm. Both the numerical simulation and comparison
experiments have been carried out to demonstrate the accuracy and feasibility of the proposed SFPDI system, high
measurement accuracy in the order of 0.1 μm, convergence rate (~90.0%) and efficiency have been realized with the
proposed method, providing a feasible way to measure three-dimensional absolute displacement in the case of no guide
rail.
Autocollimation system for measuring angular deformations with reflector designed by quaternionic method
Show abstract
Autocollimators are widely used for angular measurements in instrument-making and the manufacture of
elements of optical systems (wedges, prisms, plane-parallel plates) to check their shape parameters (rectilinearity,
parallelism and planarity) and retrieve their optical parameters (curvature radii, measure and test their flange focusing).
Autocollimator efficiency is due to the high sensitivity of the autocollimation method to minor rotations of the reflecting
control element or the controlled surface itself. We consider using quaternions to optimize reflector parameters during
autocollimation measurements as compared to the matrix technique. Mathematical model studies have demonstrated that
the orthogonal positioning of the two basic unchanged directions of the tetrahedral reflector of the autocollimator is
optimal by the criterion of reducing measurement errors where the axis of actual rotation is in a bisecting position
towards them. Computer results are presented of running quaternion models that yielded conditions for diminishing
measurement errors provided apriori information is available on the position of rotation axis.
A practical technique is considered for synthesizing the parameters of the tetrahedral reflector that employs the newly-retrieved relationships. Following the relationships found between the angles of the tetrahedral reflector and the angles of the parameters of its initial orientation, an applied technique was developed to synthesize the control element for autocollimation measurements in case apriori information is available on the axis of actual rotation during monitoring measurements of shaft or pipeline deformation.
A practical technique is considered for synthesizing the parameters of the tetrahedral reflector that employs the newly-retrieved relationships. Following the relationships found between the angles of the tetrahedral reflector and the angles of the parameters of its initial orientation, an applied technique was developed to synthesize the control element for autocollimation measurements in case apriori information is available on the axis of actual rotation during monitoring measurements of shaft or pipeline deformation.
Steps towards traceability for an asphere interferometer
I. Fortmeier,
M. Stavridis,
C. Elster,
et al.
Show abstract
Optical systems have increased in quality and capability and are today widely used in many fields of applications. An
important step forward was the introduction of aspheres and freeform surfaces. For manufacturing these surfaces in
high quality, the accurate measurement of them is highly important. A reliable measurement requires traceability.
The concept of traceability is presented, uncertainty sources are itemized and the steps towards traceability for an
asphere interferometer are discussed.
Principles of radiation terrain mapping with SiPM gamma spectrometer
Show abstract
The paper is about field and special methods of radiation terrain mapping with the identification of their distinctive features, advantages and disadvantages of each of them. The applicability of methods in various situations of radiation contamination is shown. An analysis of sources of radioactive radiation and of the situation of radiation contamination in Russia has been carried out. Different detectors of ionizing radiation are compared. It is proved that SiPM combines high performance and operational characteristics most effectively, making it possible to use it in a gamma spectrometer for any type of radiation mapping.
The spatial concentration of dust emissions measured by using 3D scanning lidar in the open storage yards of steel-making company
Show abstract
The wind-blown dust emissions frequently occur in the open storage yards of steel-making
companies. Tracking the dust source and monitoring their dispersion are rather difficult. This type of
open-air storage yards poses many environmental hazards. The 3-D scanning lidar system is effective in
environmental monitoring (e.g., dust) with high temporal and spatial resolution, which is lacking in
traditional ground-based measurement. The objective of this paper is to make an attempt for the flux
estimation of dust concentration by using lidar system. Further, we investigate the dynamical process of
dust and their relationship with local air quality monitoring data.
The results show that the material storage erosion by wind (~ 3.6 m/s) could cause dust to elevate up to 20m height above the material storage, and produces the flux of dust around 674 mg/s. The flux of dust is proportional to the dust mass concentration (PM10) measured by commercial ambient particular monitors.
The results show that the material storage erosion by wind (~ 3.6 m/s) could cause dust to elevate up to 20m height above the material storage, and produces the flux of dust around 674 mg/s. The flux of dust is proportional to the dust mass concentration (PM10) measured by commercial ambient particular monitors.
Optoelectronic joined-channel autocollimator for measuring three angular coordinates
Show abstract
The article is based on some research which is considering the three-axis angle measuring autocollimator with one
channel capable of measuring three angular coordinates simultaneously. In order to measure angular displacements
around the three main coordinate axes (OX, ОY, and ОZ), special control elements are used. The use of a special control
element generally improves the characteristics of the device, but it creates a problem of autocollimation mark
overlapping. This issue creates a zone of inoperability of the device and makes measurement and control impossible. The
ways of solving this problem are not considered in this paper. The prototype of an optoelectronic joined-channel
autocollimator with a tetrahedral control element is developed. The developed prototype passed functional testing,
calibration was conducted with using a flat mirror. The paper also shows the results of the research device accuracy in
the measurement of different angles.
Interferometric signals analysis based on the extended Kalman filter tuned by machine learning technique
Show abstract
The paper deals with the machine learning approach to automatic tuning of extended Kalman filter in application to
interferometric signals processing. The representation of interferometric signals as output of dynamic systems with
varying state vector is presented. It is shown that the challenge of the extended Kalman filter application to
interferometric data processing is selection of initial parameters for the filter. The complex tuning problem is described
in a formal form. The machine learning approach to the automatic filter tuning is proposed. The combination of Monte
Carlo optimization and the gradient descent are implemented for initial filter parameters selection. The optimization
criterion in the form of sum differences between measured and estimated signal value is presented and discussed. The
results of simulated and experimental interferometric signals processing are presented and analyzed. The quality of
amplitude and phase estimation by the automatically tuned filter is at the same level as hand tuned filter. It is shown, that
proposed approach allows to obtain robust results of experimental data processing.
The small-sized ultraprecision sensor for measuring linear displacements
Show abstract
The article describes a new optical scheme of noncontact sensor for measuring linear displacement - linear encoder.
This sensor is an optical device in which the measurement of displacement is performed by analyzing the optical signal,
which pass through two diffraction gratings, one of which is moved relative to the other. The optical signal is obtained by
the diffraction of light in these diffraction gratings and subsequent interference of diffracted beams. Often this type of
sensors are multi-channel devices with symmetrically positioned of detectors. This scheme is proposed to use a multisection
phase mask that allows to make a small-sized sensor. Sections of this multi-section phase mask are the optical
windows and they made the final interference signals to be shifted relative to each other in phase. The number of sections
in the multi-section phase mask can be varied. Estimated sufficient number of sections is four or more.
Simulation of multispectral multisource for device of consumer and medicine products analysis
Show abstract
One of the results of intensive development of led technology was the creation of a multi-component, managed
devices and illumination/irradiation used in various fields of production (e.g., food industry analysis, food
quality). The use of LEDs has become possible due to their structure determining spatial, energy, electrical,
thermal and other characteristics. However, the development of the devices for illumination/irradiation require
closer attention in the case if you want to provide precise illumination to the area of analysis, located at a
specified distance from the radiation source. The present work is devoted to the development and modelling of a
specialized source of radiation intended for solving problems of analysis of food products, medicines and water
for suitability in drinking. In this work, we provided a mathematical model of spatial and spectral distribution of
irridation from the source of infrared radiation ring structure. When you create this kind of source, you address
factors such spectral component, the power settings, the spatial and energy components of the diodes.
Online hyperspectral imaging system for evaluating quality of agricultural products
Show abstract
The consumption of fresh-cut agricultural produce in Korea has been growing. The browning of fresh-cut vegetables
that occurs during storage and foreign substances such as worms and slugs are some of the main causes of consumers’
concerns with respect to safety and hygiene. The purpose of this study is to develop an on-line system for evaluating
quality of agricultural products using hyperspectral imaging technology. The online evaluation system with single
visible-near infrared hyperspectral camera in the range of 400 nm to 1000 nm that can assess quality of both surfaces of
agricultural products such as fresh-cut lettuce was designed. Algorithms to detect browning surface were developed for
this system. The optimal wavebands for discriminating between browning and sound lettuce as well as between
browning lettuce and the conveyor belt were investigated using the correlation analysis and the one-way analysis of
variance method. The imaging algorithms to discriminate the browning lettuces were developed using the optimal
wavebands. The ratio image (RI) algorithm of the 533 nm and 697 nm images (RI533/697) for abaxial surface lettuce and
the ratio image algorithm (RI533/697) and subtraction image (SI) algorithm (SI538-697) for adaxial surface lettuce had the
highest classification accuracies. The classification accuracy of browning and sound lettuce was 100.0% and above
96.0%, respectively, for the both surfaces. The overall results show that the online hyperspectral imaging system could
potentially be used to assess quality of agricultural products.
Enhancement of spatial resolution in digital holographic microscopy using speckle field generated from ring-slit apertures
Show abstract
In this study, we propose a method to enhance the spatial resolution of digital holographic microscopy with
speckle illuminations. In this method, speckle patterns are generated from coherence light passing through ringslit
apertures instead of the most typical circular apertures, to obtain higher numerical aperture. The results
show that a reconstructed image with the higher resolution is obtained using ring-slit apertures.
Phase and group refractive indices of air calculation by fitting of phase difference measured using a combination of laser and low-coherence interferometry
Show abstract
The air refractive index is an important parameter in interferometric length measurements, since it substantially
affects the measurement accuracy. We present a refractive index of air measurement method based on monitoring
the phase difference between the ambient air and vacuum inside a permanently evacuated double-spaced cell.
The cell is placed in one arm of the Michelson interferometer equipped with two light sources—red LED and
HeNe laser, while the low-coherence and laser interference signals are measured separately. Both phase and group
refractive indices of air can be calculated from the measured signals. The method was experimentally verified by
comparing the obtained refractive index values with two different techniques.
Very high aspect ratio through silicon via reflectometry
Show abstract
Through Silicon Via (TSV) technology is a key feature of new 3D integration of circuits by creation of interconnections
using vias, which go through the silicon wafer. Typically, the highly-selective Bosch Si etch process, characterized by a
high etch rate and high aspect ratio and forming of scallops on the sidewalls is used. As presented in this paper, we have
developed an experimental setup and a respective evaluation algorithm for the control and monitoring of very high aspect
ratio TSV profiles by spectroscopic reflectometry. For this purpose square via arrays with lateral dimension from 3 to
10 μm were fabricated by a Bosch etch process and analyzed by our setup. By exploiting interference and diffraction
effects of waves reflected from the top and bottom surfaces as well as from the side walls of the TSV patterns, the
measurements provided etch depths, CD values and scallop periods. The results were compared with data obtained by a
commercial wafer metrology tool. Aspect ratios of up to 35:1 were safely evaluable by our setup.
Application of identifying transmission spheres for spherical surface testing
Show abstract
We developed a new application on Microsoft Foundation Classes (MFC) to identify correct
transmission spheres (TS) for Spherical Surface Testing (SST). Spherical surfaces are important optical
surfaces, and the wide application and high production rate of spherical surfaces necessitates an accurate
and highly reliable measuring device. A Fizeau Interferometer is an appropriate tool for SST due to its subnanometer
accuracy. It measures the contour of a spherical surface using a common path, which is
insensitive to the surrounding circumstances. The Fizeau Interferometer transmits a wide laser beam,
creating interference fringes from re-converging light from the transmission sphere and the test surface. To
make a successful measurement, the application calculates and determines the appropriate transmission
sphere for the test surface. There are 3 main inputs from the test surfaces that are utilized to determine the
optimal sizes and F-numbers of the transmission spheres: (1) the curvatures (concave or convex), (2) the
Radii of Curvature (ROC), and (3) the aperture sizes. The application will firstly calculate the F-numbers
(i.e. ROC divided by aperture) of the test surface, secondly determine the correct aperture size of a convex
surface, thirdly verify that the ROC of the test surface must be shorter than the reference surface’s ROC of
the transmission sphere, and lastly calculate the percentage of area that the test surface will be measured.
However, the amount of interferometers and transmission spheres should be optimized when measuring
large spherical surfaces to avoid requiring a large amount of interferometers and transmission spheres for
each test surface. Current measuring practices involve tedious and potentially inaccurate calculations. This
smart application eliminates human calculation errors, optimizes the selection of transmission spheres
(including the least number required) and interferometer sizes, and increases efficiency.
Investigation of accuracy characteristics of circular photodetector: Multiscan
Show abstract
This article is about the research of precision characteristics of a circular sensor "Multiscan". The research was
conducted on installation which base was a goniometer GS-5. Such characteristics as nonlinearity, stability, error
of reproducibility of results of measurements were investigated. A scheme for arranging the encoder on the basis
of a circular photodetector "Multiscan" is proposed.
High precision laser photometer for laser optics
Show abstract
Development of laser systems requires optical components with high performance, and a
high-precision double-beam laser photometer was designed and established to measure the optical
performance at 1064nm. Double beam design and lock-in technique was applied to decrease the
impact of light energy instability and electric noise. Pairs of samples were placed symmetrically to
eliminate beam displacement, and laser scattering imaging technique was applied to determine the
influence of surface defect on the optical performance. Based on the above techniques, transmittance
and reflection of pairs of optics were obtained, and the measurement precision was improved to 0.06%.
Different types of optical loss, such as total loss, volume loss, residual reflection and surface scattering
loss, were obtained from the transmittance and reflection measurement of samples with different
thickness. Comparison of optical performance of the test points with and without surface defects, the
influence of surface defects on optical performance was determined. The optical performance of
Nd-glass at 1064nm were measured as an example. Different types of optical loss and the influence of
surface defects on the optical loss was determined.
Analysis on optical heterodyne frequency error of full-field heterodyne interferometer
Show abstract
The full-field heterodyne interferometric measurement technology is beginning better applied by employing low
frequency heterodyne acousto-optical modulators instead of complex electro-mechanical scanning devices. The optical element surface could be directly acquired by synchronously detecting the received signal phases of each pixel, because standard matrix detector as CCD and CMOS cameras could be used in heterodyne interferometer. Instead of the traditional four-step phase shifting phase calculating, Fourier spectral analysis method is used for phase extracting which brings lower sensitivity to sources of uncertainty and higher measurement accuracy. In this paper, two types of full-field heterodyne interferometer are described whose advantages and disadvantages are also specified.
Heterodyne interferometer has to combine two different frequency beams to produce interference, which brings a variety of optical heterodyne frequency errors. Frequency mixing error and beat frequency error are two different kinds of inescapable heterodyne frequency errors. In this paper, the effects of frequency mixing error to surface measurement are derived. The relationship between the phase extraction accuracy and the errors are calculated.
:: The tolerance of the extinction ratio of polarization splitting prism and the signal-to-noise ratio of stray light is given. The error of phase extraction by Fourier analysis that caused by beat frequency shifting is derived and calculated. We also propose an improved phase extraction method based on spectrum correction. An amplitude ratio spectrum correction algorithm with using Hanning window is used to correct the heterodyne signal phase extraction. The simulation results show that this method can effectively suppress the degradation of phase extracting caused by beat frequency error and reduce the measurement uncertainty of full-field heterodyne interferometer.
Heterodyne interferometer has to combine two different frequency beams to produce interference, which brings a variety of optical heterodyne frequency errors. Frequency mixing error and beat frequency error are two different kinds of inescapable heterodyne frequency errors. In this paper, the effects of frequency mixing error to surface measurement are derived. The relationship between the phase extraction accuracy and the errors are calculated.
:: The tolerance of the extinction ratio of polarization splitting prism and the signal-to-noise ratio of stray light is given. The error of phase extraction by Fourier analysis that caused by beat frequency shifting is derived and calculated. We also propose an improved phase extraction method based on spectrum correction. An amplitude ratio spectrum correction algorithm with using Hanning window is used to correct the heterodyne signal phase extraction. The simulation results show that this method can effectively suppress the degradation of phase extracting caused by beat frequency error and reduce the measurement uncertainty of full-field heterodyne interferometer.
An optical flow-based method for velocity field of fluid flow estimation
Show abstract
The aim of this paper is to present a method for estimating flow-velocity vector fields using the Lucas-Kanade algorithm.
The optical flow measurements are based on the Particle Image Velocimetry (PIV) technique, which is commonly used
in fluid mechanics laboratories in both research institutes and industry. Common approaches for an optical
characterization of velocity fields base on computation of partial derivatives of the image intensity using finite
differences. Nevertheless, the accuracy of velocity field computations is low due to the fact that an exact estimation of
spatial derivatives is very difficult in presence of rapid intensity changes in the PIV images, caused by particles having
small diameters. The method discussed in this paper solves this problem by interpolating the PIV images using Gaussian
radial basis functions. This provides a significant improvement in the accuracy of the velocity estimation but, more
importantly, allows for the evaluation of the derivatives in intermediate points between pixels. Numerical analysis proves
that the method is able to estimate even a separate vector for each particle with a 5× 5 px2 window, whereas a classical
correlation-based method needs at least 4 particle images. With the use of a specialized multi-step hybrid approach to
data analysis the method improves the estimation of the particle displacement far above 1 px.
Phase detection model and method for SPR effect modulated by metallic thickness
Show abstract
A mathematic model based on surface plasmon resonance (SPR) effect is presented to measure the nano metallic film
thickness with the coupling device of Kretschmann configuration composed of K9 prism-gold film-air. Four modulation
modes of SPR method, such as intensity, phase, wavelength and angle, are numerically analyzed. Their detection
principles, the measurement range and sensitivity of different modulation type sensors are discussed. The simulation
results show that the SPR intensity detection method has the highest measurement range and the SPR phase detection
method has the highest sensitivity. In practical applications, not only the measurement range and sensitivity, but the
optical signal processing mode, experiment devices, the complexity of the algorithm and cost factors should be
considered to research and develop the appropriate thin metallic film's thickness measurement SPR sensor with higher
sensitivity and stability.
Combined narrowband imager-spectrograph with volume-phase holographic gratings
Show abstract
In the present work we discuss a possibility to build an instrument with two operation modes - spectral and imaging
ones. The key element of such instrument is a dispersive and filtering unit consisting of two narrowband volume-phase
holographic gratings. Each of them provides high diffraction efficiency in a relatively narrow spectral range of a few tens
of nanometers. Besides, the position of this working band is highly dependent on the angle of incidence. So we propose
to use a couple of such gratings to implement the two operational modes. The gratings are mounted in a collimated beam
one after another. In the spectroscopic mode the gratings are turned on such angle that the diffraction efficiency curves
coincide, thus the beams diffracted on the first grating are diffracted twice on the second one and a high-dispersion
spectrum in a narrow range is formed. If the collimating and camera lenses are corrected for a wide field it is possible to
use a long slit and register the spectra from its different points separately. In the imaging mode the gratings are turned to
such angle that the efficiency curves intersect in a very narrow wavelength range. So the beams diffracted on the first
grating are filtered out by the second one except of the spectral component, which forms the image. In this case the
instrument works without slit diaphragm on the entrance. We provide an example design to illustrate the proposed
concept. This optical scheme works in the region around 656 nm with F/# of 6.3. In the spectroscopic mode it provides a
spectrum for the region from 641 to 671 nm with reciprocal linear dispersion of 1.4 nm/mm and the spectral resolving
power higher than 14000. In the imaging mode it covers linear 12mm x 12mm field of view with spatial resolution of 15-
30 lines/mm.
Heterodyne grating interferometry based on sinusoidal phase modulation for displacement measurement
Show abstract
In this study, a heterodyne grating interferometer based on the sinusoidal phase modulation method for displacement
measurements was proposed. The interference beams were modulated using a sinusoidal oscillating grating, and the
proposed frequency-domain quadrature detection method was used to detect the optical phase of the interferometer
and determine the displacement. Experimental results were consistent with the strain gauge results for several
displacement ranges. When only high-frequency noise was considered, our method achieved a measurement
resolution of approximately 2 nm.
Optical exploration of micro/nanoscale irregularities created on metallic surfaces by femtosecond laser irradiation
Show abstract
In this paper, we suggest a direct method based on light scattering and Beckmann formulation for the coarse surface
RMS roughness and correlation length measurements. Metallic steel samples irradiated under controlled interaction
conditions with ultrafast femtosecond laser system are selected as the random rough surfaces for investigation. Stabilized
low-intensity He-Ne laser and an appropriate power meter are selected as the main elements of the experimental
measurement probe. The light source and detector are located symmetrically around the surface normal and the reflected
light is collected to be used in Beckmann formulation. In this regard, the dependency of the surface scattering to the
illumination angle is also investigated. Atomic Force Microscopy and Scanning Electron Microscopy are utilized as
standard common methods to extract the surface features and check the reliability of the theoretical approach.
Universal dynamic goniometer for rotary encoders
Nikolai V. Smirnov,
Svjatoslav M. Latyev,
Anastasiia I. Naumova
Show abstract
A novel dynamic goniometer for the accuracy of rotary encoders has been developed on the base of the method of comparison with the reference encoder. The set-up of the goniometer considers all constructive and informative characteristics of measured encoders. The novel goniometer construction uses the new compensating method of instrumental errors in automatic working process. The advantages of the dynamic goniometer in combination with an optical rotary encoder at the reduction of the measuring time and a simultaneous increase of the accuracy.
Estimation of clearances in the design and adjustment of barrel type lens systems
Show abstract
Estimation of probable clearances in the fit of the installed lenses and the impact from mounting and adjustment of
units on system alignment and the resulting imaging quality has been considered. The characters of dispersion fields and
acceptable deviations in mating dimensions of parts and their allowance have been analyzed for the estimation of
probable clearances. Very commonly existing deviations in the clearances have a considerable systematic component
due to systematic components of errors in the mated dimensions of parts. It has been shown that the assembly of lens
based optical systems in horizontal position of its body allows vast reduction of the impact given by clearances on the
accuracy of the alignment of the lens parts as compared to assembly in vertical position of its body, as in the this case the
lens misalignment is due to errors in the diameters of lens components. For the adjustment of the quality of the image
generated by the optical system it is necessary to take into account both the impact from misalignment of lens
components on edge and central aberrations of the image field.
Self-tunable phase shifting algorithm for images with additive noise
Show abstract
Phase-shifting is a well-known technique for phase retrieval that requires a series of intensity measurements with
certain phase-steps. Additive noise is one of the most important source of errors in interferometry. In this
work we present a systematic algebraic approach for the generation of self-tunable phase shifting algorithms that
minimize the propagation of additive noise.
Revealing features of different optical shaping technologies by a point diffraction interferometer
Show abstract
Almost hidden residual defects of a test surface can be revealed using high precision instrument such as a point
diffraction interferometer (PDI). In general, PDI is engaged to display the figure of a surface or wavefront with subnanometer
accuracy paying attention to low-frequency configurations. Such technique is suited to test EUV or X-ray
optics. The tool described in the paper is able to map absolute profile deviations of several angstroms and therefore it
provides a new vision of a surface under test of various quality, e.g. detects specific characteristics which immediately
disclose either lapping or diamond turning has been used to form the substrate. Such inspection may help optimize the
processes in early stage of shape forming before final configuring.
Pointwise intensity-based dynamic speckle analysis with binary patterns
Show abstract
Non-destructive detection of physical or biological activity through statistical processing of speckle patterns on the
surface of diffusely reflecting objects is an area of active research. A lot of pointwise intensity-based algorithms have
been proposed over the recent years. Efficiency of these algorithms is deteriorated by the signal-dependent speckle data,
non-uniform illumination or varying reflectivity across the object, especially when the number of the acquired speckle
patterns is limited. Pointwise processing of a sequence of 2D images is also time-consuming. In this paper, we propose to
transform the acquired speckle images into binary patterns by using for a sign threshold the mean intensity value
estimated at each spatial point from the temporal sequence of intensities at this point. Activity is characterized by the 2D
distribution of a temporal polar correlation function estimated at a given time lag from the binary patterns. Processing of
synthetic and experimental data confirmed that the algorithm provided correct activity determination with the same
accuracy as the temporal normalized correlation function. It is efficient without the necessity to apply normalization at
non-uniform distribution of intensity in the illuminating laser beam and offers acceleration of computation.
Full-field wafer warpage measurement technique
Show abstract
An innovative moiré technique for full-field wafer warpage measurement is proposed in this study. The wafer warpage
measurement technique is developed based on moiré method, Talbot effect, scanning profiling method, stroboscopic,
instantaneous phase-shift method, as well as four-step phase shift method, high resolution, high stability and full-field
measurement capabilities can be easily achieved. According to the proposed full-field optical configuration, a laser beam
is expanded into a collimated beam with a 2-inch diameter and projected onto the wafer surface. The beam is reflected
by the wafer surface and forms a moiré fringe image after passing two circular gratings, which is then focused and
captured on a CCD camera for computation. The corresponding moiré fringes reflected from the wafer surface are
obtained by overlapping the images of the measuring grating and the reference grating. The moiré fringes will shift when
wafer warpage occurs. The phase of the moiré fringes will change proportionally to the degree of warpage in the wafer,
which can be measured by detecting variations in the phase shift of the moiré fringes in each detection points on the
surface of the entire wafer. The phase shift variations of each detection points can be calculated via the instantaneous
phase-shift method and the four-step phase-shift method. By adding up the phase shift variations of each detection points
along the radii of the circular gratings, the warpage value and surface topography of the wafer can be obtained.
Experiments show that the proposed method is capable of obtaining test results similar to that of a commercial sensor, as
well as performing accurate measurements under high speed rotation of 1500rpm. As compared to current warpage
measurement methods such as the beam optical method, confocal microscopy, laser interferometry, shadow moiré
method, and structured light method, this proposed technique has the advantage of full-field measurement, high
resolution, stability and adaptability.
Vibration compensated high-resolution scanning white-light Linnik-interferometer
Show abstract
We present a high-resolution Linnik scanning white-light interferometer (SWLI) with integrated distance measuring
interferometer (DMI) for close-to-machine applications in the presence of environmental vibrations. The distance,
measured by DMI during the depth-scan, is used for vibration compensation of SWLI signals. The reconstruction of the
white-light interference signals takes place after measurement by reordering the captured images in accordance with their
real positions obtained by the DMI and subsequent trigonometrical approximation. This system is the further development
of our previously presented Michelson-interferometer. We are able to compensate for arbitrary vibrations with frequencies
up to several kilohertz and amplitudes in the lower micrometer range. Completely distorted SWLI signals can be
reconstructed and the surface topography can be obtained with high accuracy. We demonstrate the feasibility of the method
by examples of practical measurements with and without vibrational disturbances.
Features of the estimation of temperature distribution on the bead formed by the laser aided metal powder deposition
Show abstract
The estimation of temperature variations in five regions of layer track is fulfilled in two different cases of layer track
formation: laser aided metal powder deposition and selective laser melting with a pre-deposited layer of metal powder.
The peculiarities of the multichannel pyrometer have been described, and the advantages of the application of spectralratio
pyrometer in diagnostics in the additive laser technologies have been demonstrated. A set of measurements of the
temperature distribution in the region of exposure to laser radiation during a bead formation in technology of laser aided
metal powder deposition with powder injection has been performed at the specific energy input of J=90 MJ/kg. The
dependences of the temperature on scanning velocity, laser power and powder thickness have been derived in the
technology of selective laser melting. It has been shown that the maximum temperature of the track surface is little
changed in the wide range of variation of the calculated parameter of specific energy input J=4…20 MJ/kg, the bead
width is here increased as J grows. The increase of J above a certain value J0 leads to a rise in the temperature at the bead
axis. For the experimental conditions with the track width around 1 mm, the character value is estimated as J0 =
24 MJ/kg. It has been shown that J0 depends inversely on the track width.
Optical fiber sensors measurement system and special fibers improvement
Show abstract
We present method for the improvement of the measurement accuracy in the optical frequency spectra
measurements based on tunable optical filters. The optical filter was used during the design and realization of the
measurement system for the inspection of the fiber Bragg gratings. The system incorporates a reference block for the
compensation of environmental influences, an interferometric verification subsystem and a PC - based control software
implemented in LabView. The preliminary experimental verification of the measurement principle and the measurement
system functionality were carried out on a testing rig with a specially prepared concrete console in the UJV Řež. The
presented system is the laboratory version of the special nuclear power plant containment shape deformation
measurement system which was installed in the power plant Temelin during last year.
On the base of this research we started with preparation other optical fiber sensors to nuclear power plants measurement. These sensors will be based on the microstructured and polarization maintaining optical fibers. We started with development of new methods and techniques of the splicing and shaping optical fibers. We are able to made optical tapers from ultra-short called adiabatic with length around 400 um up to long tapers with length up to 6 millimeters.
We developed new techniques of splicing standard Single Mode (SM) and Multimode (MM) optical fibers and splicing of optical fibers with different diameters in the wavelength range from 532 to 1550 nm. Together with development these techniques we prepared other techniques to splicing and shaping special optical fibers like as Polarization-Maintaining (PM) or hollow core Photonic Crystal Fiber (PCF) and theirs cross splicing methods with focus to minimalize backreflection and attenuation. The splicing special optical fibers especially PCF fibers with standard telecommunication and other SM fibers can be done by our developed techniques. Adjustment of the splicing process has to be prepared for any new optical fibers and new fibers combinations. The splicing of the same types of fibers from different manufacturers can be adjusted by several tested changes in the splicing process. We are able to splice PCF with standard telecommunication fiber with attenuation up to 2 dB. The method is also presented.
Development of these new techniques and methods of the optical fibers splicing are made with respect to using these fibers to another research and development in the field of optical fibers sensors, laser frequency stabilization and laser interferometry based on optical fibers. Especially for the field of laser frequency stabilization we developed and present new techniques to closing microstructured fibers with gases inside.
On the base of this research we started with preparation other optical fiber sensors to nuclear power plants measurement. These sensors will be based on the microstructured and polarization maintaining optical fibers. We started with development of new methods and techniques of the splicing and shaping optical fibers. We are able to made optical tapers from ultra-short called adiabatic with length around 400 um up to long tapers with length up to 6 millimeters.
We developed new techniques of splicing standard Single Mode (SM) and Multimode (MM) optical fibers and splicing of optical fibers with different diameters in the wavelength range from 532 to 1550 nm. Together with development these techniques we prepared other techniques to splicing and shaping special optical fibers like as Polarization-Maintaining (PM) or hollow core Photonic Crystal Fiber (PCF) and theirs cross splicing methods with focus to minimalize backreflection and attenuation. The splicing special optical fibers especially PCF fibers with standard telecommunication and other SM fibers can be done by our developed techniques. Adjustment of the splicing process has to be prepared for any new optical fibers and new fibers combinations. The splicing of the same types of fibers from different manufacturers can be adjusted by several tested changes in the splicing process. We are able to splice PCF with standard telecommunication fiber with attenuation up to 2 dB. The method is also presented.
Development of these new techniques and methods of the optical fibers splicing are made with respect to using these fibers to another research and development in the field of optical fibers sensors, laser frequency stabilization and laser interferometry based on optical fibers. Especially for the field of laser frequency stabilization we developed and present new techniques to closing microstructured fibers with gases inside.
Broadband interferometric characterisation of nano-positioning stages with sub-10 pm resolution
Show abstract
A traceable calibration setup for investigation of the quasi-static and the dynamic performance of nano-positioning
stages is detailed, which utilizes a differential plane-mirror interferometer with double-pass configuration from the
National Physical Laboratory (NPL). An NPL-developed FPGA-based interferometric data acquisition and decoding
system has been used to enable traceable quasi-static calibration of nano-positioning stages with high resolution. A lockin
based modulation technique is further introduced to quantitatively calibrate the dynamic response of moving stages
with a bandwidth up to 100 kHz and picometer resolution. First experimental results have proven that the calibration
setup can achieve under nearly open-air conditions a noise floor lower than 10 pm/sqrt(Hz). A pico-positioning stage,
that is used for nanoindentation with indentation depths down to a few picometers, has been characterized with this
calibration setup.
Signal-to-noise ratio for mode-mode fiber interferometer
Oleg Kotov,
Ivan Chapalo
Show abstract
In this paper we focus on the subject of signal-to-noise ratio (SNR) estimation for mode-mode fiber interferometer (MFI).
The main problem of this issue is MFI signal fading which leads to unstable response and transfer function of MFI and
does not allow correct SNR evaluation. To solve this problem the method of normalized averaged characteristics is
developed and applied. SNR dependencies on different MFI parameters and for different cases of fiber launching
conditions are calculated and analyzed.
The design of the layout of faceted multi-channel electro-optical spatial coordinates measuring instrument for point-like bright objects
Show abstract
For many applied problems it is necessary to obtain information about the situation in a wide angular field in order to
measure various parameters of objects: their spatial coordinates, instantaneous velocities, and so on. In this case, one
interesting bionic approach can be used – a mosaic (or discrete, otherwise, facet) angular field. Such electro-optical
system constructively imitates the visual apparatus of insects: many photodetectors like ommatidia (elements of the facet
eye structure) are located on a non-planar surface. Such devices can be used in photogrammetry and aerial photography
systems (if the space is sufficient), in the transport sector as vehicle orientation organs, as systems for monitoring in
unmanned aerial vehicles, in endoscopy for obtaining comprehensive information on the state of various cavities, in
intelligent robotic systems. In this manuscript discusses the advantages and disadvantages of multi-channeled
optoelectronic systems with a mosaic angular field, presents possible options for their use, and discusses some of the
design procedures performed when developing a layout of a coordinate measuring device.
Analysis and 3D inspection system of drill holes in aeronautical surfaces
Show abstract
In aerospace industry, the structure of the aircraft is assembled using small parts or a combination of them that are made
with different materials, such as for instance aluminium, titanium, composites or even 3D printed parts. The union
between these small parts is a critical point for the integrity of the aircraft. The quality of this union will decide the
fatigue of adjacent components and therefore the useful life of them. For the union process the most extended method is
the rivets, mainly because their low cost and easy manufacturing. For this purpose it is necessary to made drill holes in
the aeronautical surface to insert the rivets.
In this contribution, we present the preliminary results of a 3D inspection system [1] for drill holes analysis in aeronautical surfaces. The system, based in optical triangulation, was developed by the Group of Optoelectronic Image Processing from the University of Valencia in the framework of the Airbus Defence and Space (AD&S), MINERVA project (Manufacturing industrial - means emerging from validated automation). The capabilities of the system permits to generate a point cloud with 3D information and GD&T (geometrical dimensions and tolerances) characteristics of the drill hole. For the inner surface defects detection, the system can generate an inner image of the drill hole with a scaled axis to obtain the defect position. In addition, we present the analysis performed for the drills in the wing station of the A-400 M. In this analysis the system was tested for diameters in the range of [10 – 15.96] mm, and for Carbon Fibre.
In this contribution, we present the preliminary results of a 3D inspection system [1] for drill holes analysis in aeronautical surfaces. The system, based in optical triangulation, was developed by the Group of Optoelectronic Image Processing from the University of Valencia in the framework of the Airbus Defence and Space (AD&S), MINERVA project (Manufacturing industrial - means emerging from validated automation). The capabilities of the system permits to generate a point cloud with 3D information and GD&T (geometrical dimensions and tolerances) characteristics of the drill hole. For the inner surface defects detection, the system can generate an inner image of the drill hole with a scaled axis to obtain the defect position. In addition, we present the analysis performed for the drills in the wing station of the A-400 M. In this analysis the system was tested for diameters in the range of [10 – 15.96] mm, and for Carbon Fibre.
Measuring horizontal atmospheric turbulence at ground level from optical turbulence generator (OTG) using a 1D sensor
Show abstract
Different theories including Kolmogorov have been valid to explain and model physic phenomenal like vertical atmospheric turbulence. In horizontal path, we still have many questions, due to weather problems and consequences that it generates. To emulate some conditions of environment, we built an Optical Turbulence Generator (OTG) having spatial, humidity and temperature, measurements that were captured in the same time from optical synchronization. This development was made using digital modules as ADC (Analog to Digital Converters) and communications protocol as SPI. We all made from microcontrollers. On the other hand, to measure optical signal, we used a photomultiplier tube (PMT) where captured the intensity of fringes that shifted with a known frequency.
Outcomes show temporal shift and phase drive from dependent samples (in time domain) that correspond with frozen turbulence given by Taylor theory. Parameters studied were C2n, scintillation and inner scale in temporal patterns and analysis of their relationship with the physical associated variables. These patterns were taken from Young Interferometer in laboratory room scale. In the future, we hope with these studies, we will can implement an experiment to characterize atmospheric turbulence in a long distance, placed in the equatorial weather zone.
Outcomes show temporal shift and phase drive from dependent samples (in time domain) that correspond with frozen turbulence given by Taylor theory. Parameters studied were C2n, scintillation and inner scale in temporal patterns and analysis of their relationship with the physical associated variables. These patterns were taken from Young Interferometer in laboratory room scale. In the future, we hope with these studies, we will can implement an experiment to characterize atmospheric turbulence in a long distance, placed in the equatorial weather zone.
Superresolution imaging in spatially multiplexed interferometric microscopy by using time multiplexing
Show abstract
We report on the merging between our recently introduced SMIM (initials incoming from Spatially-Multiplexed
Interferometric Microscopy) technique and superresolution imaging. SMIM has been previously reported [Opt. Express
22, 14929 (2014); J. Bio. Opt. 21, 106007 (2016)] as a low cost, extremely simple, and highly stable scheme to update a
standard microscope into a holographic microscope but, as consequence, the usable FOV is reduced. Superresolution
capability enables to enhance the resolution limit in the usable FOV thus compensating the FOV reduction. In this
contribution, superresolution is implemented joint together with SMIM defining a new method named as S2MIM
(initials incoming from Superresolved Spatially Multiplexed Interferometric Microscopy) which updates a commercially
available non-holographic microscope into a superresolved holographic one. Experimental validation is presented for an
Olympus BX-60 upright microscope with a USAF resolution test target as calibration object.
Water turbidity optical meter using optical fiber array for topographical distribution analysis
Show abstract
This work is presenting an analysis study for using optical fiber array as turbidity meter and topographical distribution.
Although many studies have been figure out of utilizing optical fibers as sensors for turbidity measurements, still the
topographical map of suspended particles in water as rare as expected among all of works in literatures in this scope. The
effect of suspended particles are highly affect the water quality which varies according to the source of these particles. A
two dimensional array of optical fibers in a 1 litter rectangular plastic container with 2 cm cladding off sensing portion
prepared to point out 632.8 nm laser power at each fiber location at the container center. The overall output map of the
optical power were found in an inhomogeneous distribution such that the top to down layers of a present water sample
show different magnitudes. Each sample prepared by mixing a distilled water with large grains sand, small grains sand,
glucose and salt. All with different amount of concentration which measured by refractometer and turbidity meter. The
measurements were done in different times i.e. from 10 min to 60 min. This is to let the heavy particles to move down
and accumulate at the bottom of the container. The results were as expected which had a gradually topographical map
from low power at top layers into high power at bottom layers. There are many applications can be implemented of this
study such as transport vehicles fuel meter, to measure the purity of tanks, and monitoring the fluids quality in pipes.
Uncertainty analysis of optical components absorption coefficient measurement using an intra-cavity device
Show abstract
In order to measure the absorption coefficient and performance degradation characteristics of optical components which
used in high power laser system, an intra-cavity device was established based on a discharge-drived CW chemical laser.
Two pieces of 45 degree reflecting mirrors were tested. Each mirror was tested for more than twenty times, and high
power laser irradiation on the testing mirrors lasted 100 seconds continuously in each test. The dependence of absorption
coefficients on irradiation times was acquired. The testing results of both reflecting mirrors showed that, the differences
between the experimental absorption coefficients and their fitting curve were up to 30.7% and 21.6% respectively, and
the differences were independent of irradiation condition, such as irradiation energy, irradiation power and beam crosssectional
area. The uncertainty of absorption coefficient was composed of two parts. For one thing, the uncertainty of the
direct measurement results, such as the temperature rise of optical components, can cause the uncertainty of absorption
coefficients. This part of uncertainty was about 11.3%. For another, the resonant cavity need to be adjusted again when
other optical components were replaced, which lead to the change of the incident angle of the optical components to be
measured. A typical film system of 24 layers (12 pairs) was calculated by Thin Film Design Software called TFCalc,
which showed the absorption coefficients increased with the increase of incident angle. When the angle of incidence was
0.5 degree from the design value, there would be -60~71ppm difference of absorption coefficient from the original one,
and the uncertainty was 14.5%. When there was a deviation of 1 degree, the difference of absorption coefficient and the
uncertainty were -112~155ppm and 31.7% respectively. This results showed that, the deviation of incident angle was
between 0.5~1 degree in the test. In order to reduce the testing uncertainty of absorption coefficients, the deviation
between the incident angle of optical components and the design value should be reduced as much as possible. This
provides guidance for measuring the absorption coefficients of optical components with an intra-cavity device.
Invariant electro-optical system for deflection measurement of floating docks
Show abstract
An electro-optical system for deflection measurement of floating docks is represented in this paper. This system contains
a base unit with two measurement channels observing opposite directions of the dock. It also includes a set of reference
marks and an industrial computer. The measurement unit contains of a camera with long focal-length lens and a beam
splitter. The effect of the beam splitter turning point on the image position of the reference mark on the camera is
analyzed as well in this paper.
Numerical analysis of nonlinear multimode interference waveguide as a refractive index sensor
Show abstract
A numerical analysis of a refractive index sensor based on multimode interference (MMI) waveguide has been
performed in this paper. The nonlinear refractive index of graphene in the proposed sensor was investigated by applying
external electric field on the graphene cladding layer. The designed waveguide was constructed using silicon oxide
(SiO2) as substrate and silicon as a core while graphene is coated on top of the waveguide slab. The response of the
sensor in the output power was examined and validated by changing liquid samples with different refractive index. The
guided modes of the 1550 nm input plane source at the absence of external electric field were used as the initial
reference point. It is found that there was a threshold magnitude of the field which makes graphene sensitive to the
relative change in the refractive index of the solution. The output results showed a promising indication that this design
is appropriate for environmental monitoring.
Investigation of the relative orientation of the system of optical sensors to monitor the technosphere objects
Show abstract
In connection with the development of robotics have become increasingly popular variety of three-dimensional
reconstruction of the system mapping and image-set received from the optical sensors. The main objective of technical
and robot vision is the detection, tracking and classification of objects of the space in which these systems and robots
operate [15,16,18]. Two-dimensional images sometimes don’t contain sufficient information to address those or other
problems: the construction of the map of the surrounding area for a route; object identification, tracking their relative
position and movement; selection of objects and their attributes to complement the knowledge base. Three-dimensional
reconstruction of the surrounding space allows you to obtain information on the relative positions of objects, their shape,
surface texture. Systems, providing training on the basis of three-dimensional reconstruction of the results of the
comparison can produce two-dimensional images of three-dimensional model that allows for the recognition of volume
objects on flat images. The problem of the relative orientation of industrial robots with the ability to build threedimensional
scenes of controlled surfaces is becoming actual nowadays.
Evaluation of laser ablation crater relief by white light micro interferometer
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A multi-view scanning method is suggested to assess a complicated surface relief by white light interferometer.
Peculiarities of the method are demonstrated on a special object in the form of quadrangular pyramid cavity, which is
formed at measurement of micro-hardness of materials using a hardness gauge. An algorithm of the joint processing of
multi-view scanning results is developed that allows recovering correct relief values. Laser ablation craters were studied
experimentally, and their relief was recovered using the developed method. It is shown that the multi-view scanning
reduces ambiguity when determining the local depth of the laser ablation craters micro relief. Results of experimental
studies of the multi-view scanning method and data processing algorithm are presented.
Relationship of parameters of optical equisignal zone system for providing constant static characteristics
Show abstract
The paper deals with a type of optical-electronic instruments based on the optical equisignal zone. For the most
applications the difference signal in the equisignal zone is required to be independent on the distance. The purpose of the
study is to find interrelation of parameters of an optical system, of sources and of the receiving part providing constant
difference signal. It is known that if the source has a uniform radiance and an ideal objective (without aberrations) is
used, in order the width of the transitional zone be independent on the distance, the objective must be focused on infinity.
In practice homocentricity of the pencil of rays is influenced by the spherical aberration. Study of impact of the 3th order
abberrations on the width of the transitional zone, and as a result, on radiance distribution, allowed to find equations
linking the width of the transitional zone, exit pupil diameter, and irradiance of the sources. It is shown that the relative
difference signal depends on relation of the product of spherical aberration value and distance to the exit pupil diameter,
thus relative difference signal can be reduced with refocusing on a required distance. Based on obtained relations and
experimental results we conclude that using an appropriate processing of the difference signal, correction of spherical
aberration of the objective and focusing the projector into infinity, constant static characteristics may be achieved.
Estimation of the particle concentration in hydraulic liquid by the in-line automatic particle counter based on the CMOS image sensor
Show abstract
Modern hydraulic systems should be monitored on the regular basis. One of the most effective ways to address this task
is utilizing in-line automatic particle counters (APC) built inside of the system. The measurement of particle
concentration in hydraulic liquid by APC is crucial because increasing numbers of particles should mean functional
problems. Existing automatic particle counters have significant limitation for the precise measurement of relatively low
concentration of particle in aerospace systems or they are unable to measure higher concentration in industrial ones. Both
issues can be addressed by implementation of the CMOS image sensor instead of single photodiode used in the most of
APC. CMOS image sensor helps to overcome the problem of the errors in volume measurement caused by inequality of
particle speed inside of tube. Correction is based on the determination of the particle position and parabolic velocity
distribution profile. Proposed algorithms are also suitable for reducing the errors related to the particles matches in
measurement volume. The results of simulation show that the accuracy increased up to 90 per cent and the resolution
improved ten times more compared to the single photodiode sensor.
The research of the cross-links effect influence in the color matrix photodetector on an error of the air tract vertical temperature gradient determination
Show abstract
The research of the cross-links effect influence in the color matrix photodetector on an error of the air tract vertical
temperature gradient determination is provided. It is invited to consider the influence of the signals from matrix
photodetector channels on each other. There is a method to determine the value of the cross-links effect ant its influence
on the energy center coordinates determination.
Parameter optimization of measuring and control elements in the monitoring systems of complex technical objects
Show abstract
In the world is the widespread adoption of measuring equipment of new generation, which is characterized by small size,
high automation level, a multi-channel, digital filtering, satellite synchronization, wireless communication, digital record
in long-term memory with great resource, powered by long-lived sources, etc. However, modern equipment base of the
Russian institutions and the level of development of technical facilities and measuring technologies lag far behind
developed countries. For this reason, the vacated niches are actively developed by foreign companies. For example, more
than 70% instrumentation performing works on the territory of Russia, equipped with imported equipment (products of
Sweden and Germany companies); the amount of work performed with German equipment is more than 70% of the total
volume of these works; more than 80% of industrial measurements are performed using HEXAGON equipment (Sweden).
These trends show that the Russian sector of measuring technology gradually become import-dependent, which poses a
threat to the economic security of the country and consistent with national priorities.
The results of the research will allow to develop the theory of formation of control systems of the displacement with high accuracy and unattainable for the existing analogue ergonomic and weight characteristics combined with a comparable or lower cost. These advantages will allow you to be successful competition, and eventually to supplant the existing system, which had no fundamental changes in the last 20 years and, therefore, retained all the drawbacks: large size and weight, high power consumption, the dependence on magnetic fields
The results of the research will allow to develop the theory of formation of control systems of the displacement with high accuracy and unattainable for the existing analogue ergonomic and weight characteristics combined with a comparable or lower cost. These advantages will allow you to be successful competition, and eventually to supplant the existing system, which had no fundamental changes in the last 20 years and, therefore, retained all the drawbacks: large size and weight, high power consumption, the dependence on magnetic fields
Deep sub-wavelength metrology for advanced defect classification
Show abstract
Particle defects are important contributors to yield loss in semi-conductor manufacturing. Particles need to be detected
and characterized in order to determine and eliminate their root cause. We have conceived a process flow for advanced
defect classification (ADC) that distinguishes three consecutive steps; detection, review and classification. For defect
detection, TNO has developed the Rapid Nano (RN3) particle scanner, which illuminates the sample from nine azimuth
angles. The RN3 is capable of detecting 42 nm Latex Sphere Equivalent (LSE) particles on XXX-flat Silicon wafers. For
each sample, the lower detection limit (LDL) can be verified by an analysis of the speckle signal, which originates from
the surface roughness of the substrate. In detection-mode (RN3.1), the signal from all illumination angles is added. In
review-mode (RN3.9), the signals from all nine arms are recorded individually and analyzed in order to retrieve
additional information on the shape and size of deep sub-wavelength defects. This paper presents experimental and
modelling results on the extraction of shape information from the RN3.9 multi-azimuth signal such as aspect ratio,
skewness, and orientation of test defects.
Both modeling and experimental work confirm that the RN3.9 signal contains detailed defect shape information. After
review by RN3.9, defects are coarsely classified, yielding a purified Defect-of-Interest (DoI) list for further analysis on
slower metrology tools, such as SEM, AFM or HIM, that provide more detailed review data and further classification.
Purifying the DoI list via optical metrology with RN3.9 will make inspection time on slower review tools more efficient.
Effects of the density and homogeneity in NIRS crop moisture estimation
Show abstract
Near-infrared spectroscopy (NIRS) is widely used in fruits and vegetables quality evaluation. This technique is also used for the analysis of alfalfa, a crop that occupies a position of great importance in the agricultural field. In particular for the storage, moisture content is a key parameter for the crops and for this reason its monitoring is very important during the harvesting phase. Usually optical methods like NIRS are well suitable in laboratory frameworks where the specimen is properly prepared, while their application during the harvesting phase presents several diffculties. A lot of influencing factors, such as density and degree of homogeneity can affect the moisture evaluation. In this paper we present the NIRS analysis of alfalfa specimens with different values of moisture and density, as well as the obtained results. To study scattering and absorption phenomena, the forward and backward scattered light from the sample have been spectrally analyzed.
System testing for the Fresnel-lens-based optical concentrator for photovoltaic (CPV) solar energy harvesting
Show abstract
We designed, developed, fabricated, and tested an opto-electronic system to test alignment of CPV solar system
modules that is portable and robust to implement as a step in the assembly line. In addition to the components used
in systems employed previously, we implement a thin prism in four orientations in a plane normal to optical axis of
the unit under test. Its advantage is robustness against its positioning and orientation errors.
Direct fabrication of polymer micro-lens array
Show abstract
In order to break the rigidity of classic lithographic techniques, a flexible pyro-electric-electrohydrodynamic (EHD) inkjet
printing is presented. In particular, here is showed a method able to manipulate highly viscous polymers, usable for
optical integrated devices. The system proposed reaches spatial resolution up to the nano-scale and can print, for
instance, nano-particles and high viscous polymer solutions. This technique allows writing patterns directly onto a
substrate of interest in 2D or in 3D configuration and is studied in order to overcome limitations in terms of type of
materials, geometry and thickness of the substrate. In the present work, we show the potential of pyro-EHD printing in
fields as optics and micro-fluidics. A micro-channel chip is functionalized with a PDMS-made micro-lenses array,
directly printed on the chip. The geometric properties and the quality of the lenses are evaluated by a Digital Holography
(DH) analysis.
Optical fibre-based reflective displacement sensor: computer modelling and application to impact detection in aeronautical structures
Show abstract
Impact detection is used as proof of concept to demonstrate that the design principle of optical fibre-based reflective
displacement sensors is versatile enough to fit applications that go beyond the original concept for which they were
designed, i.e. Tip Clearance and Tip Timing. For that, a custom software has been created that allows to find the best
fibre arrangement within the fibre bundle that matches the specifications of the target application. After fabricating the
fibre bundle, the validity and usefulness of the simulations have been assessed by means of laboratory measurements on
the reflective displacement sensor. Finally some preliminary impact tests have been carried out to confirm the previous
work.
Characterization of laser damage performance of fused silica using photothermal absorption technique
Show abstract
The subsurface damage and metal impurities have been the main laser damage precursors of fused
silica while subjected to high power laser irradiation. Light field enhancement and thermal
absorption were used to explain the appearance of damage pits while the laser energy is far
smaller than the energy that can reach the intrinsic threshold of fused silica. For fused silica optics
manufactured by magnetorheological finishing or advanced mitigation process, no scratch-related
damage site occurs can be found on the surface.
In this work, we implemented a photothermal absorption technique based on thermal lens method to characterize the subsurface defects of fused silica optics. The pump beam is CW 532 nm wavelength laser. The probe beam is a He-Ne laser. They are collinear and focused through the same objective. When pump beam pass through the sample, optical absorption induces the local temperature rise. The lowest absorptance that we can detect is about the order of magnitude of 0.01 ppm. When pump beam pass through the sample, optical absorption induces the local temperature rise.
The photothermal absorption value of fused silica samples range from 0.5 to 10 ppm. The damage densities of the samples were plotted. The damage threshold of samples at 8J/cm2 were gived to show laser damage performance of fused silica.The results show that there is a strong correlation between the thermal absorption and laser damage density. The photothermal absorption technique can be used to predict and evaluate the laser damage performance of fused silica optics.
In this work, we implemented a photothermal absorption technique based on thermal lens method to characterize the subsurface defects of fused silica optics. The pump beam is CW 532 nm wavelength laser. The probe beam is a He-Ne laser. They are collinear and focused through the same objective. When pump beam pass through the sample, optical absorption induces the local temperature rise. The lowest absorptance that we can detect is about the order of magnitude of 0.01 ppm. When pump beam pass through the sample, optical absorption induces the local temperature rise.
The photothermal absorption value of fused silica samples range from 0.5 to 10 ppm. The damage densities of the samples were plotted. The damage threshold of samples at 8J/cm2 were gived to show laser damage performance of fused silica.The results show that there is a strong correlation between the thermal absorption and laser damage density. The photothermal absorption technique can be used to predict and evaluate the laser damage performance of fused silica optics.
Compensation of optical system distortion and image perspective deformations for the projection lens
Show abstract
In the article takes up the possibility of optical system distortion compensation for projection lens by making
predistortions into projected digital image. Image processing is producing for main types of optical system distortion,
which can be described both as power polynomial and as Zernike polynomials.
Special attention is given for perspective deformations which arise in the deviation of the optical axis from perpendicular to the plane of projection. In processing takes into account both as horizontal and as vertical perspective deformation.
For possibility of optical system distortion compensation there is a need to provisional certification of lens by Abbe grid for taking polynomial description of distortion. According to certification results performed image processing on the points corresponding to the nodes of the grid Abbe. As a result of processing a digital image deformations introduced, the reverse occurring when deformations are projecting.
Pre-made image deformations allow to compensate for distortion of optical system and the perspective deformation caused by the projection lens used, therefore, when projecting the image will largely corresponds to the original image. The results of the work is planning to use in the preparation of digital image mapping show, namely the projection on objects of complex geometric shapes.
Special attention is given for perspective deformations which arise in the deviation of the optical axis from perpendicular to the plane of projection. In processing takes into account both as horizontal and as vertical perspective deformation.
For possibility of optical system distortion compensation there is a need to provisional certification of lens by Abbe grid for taking polynomial description of distortion. According to certification results performed image processing on the points corresponding to the nodes of the grid Abbe. As a result of processing a digital image deformations introduced, the reverse occurring when deformations are projecting.
Pre-made image deformations allow to compensate for distortion of optical system and the perspective deformation caused by the projection lens used, therefore, when projecting the image will largely corresponds to the original image. The results of the work is planning to use in the preparation of digital image mapping show, namely the projection on objects of complex geometric shapes.
A flexible 3D laser scanning system using a robotic arm
Show abstract
In this paper, we present a flexible 3D scanning system based on a MEMS scanner mounted on an industrial arm with a
turntable. This system has 7-degrees of freedom and is able to conduct a full field scan from any angle, suitable for
scanning object with the complex shape. The existing non-contact 3D scanning system usually uses laser scanner that
projects fixed stripe mounted on the Coordinate Measuring Machine (CMM) or industrial robot. These existing systems
can’t perform path planning without CAD models. The 3D scanning system presented in this paper can scan the object
without CAD models, and we introduced this path planning method in the paper. We also propose a practical approach to
calibrating the hand–in-eye system based on binocular stereo vision and analyzes the errors of the hand-eye calibration.
A high-performance fringe pattern generation method for fringe projection profilometry
Show abstract
Fringe projection profilometry (FPP) has been one of the most popular non-contact methods for 3D surface measurement
in recent years. In FPP, the quality of the fringe pattern determines the measurement accuracy and measurement range to
a great extent. In this paper, we proposed a high-quality fringe projection method using a biaxial MEMS scanning mirror
and a laser diode (LD). The fringe pattern is produced by a very low NA (numerical aperture) scanning laser beam.
Compared with pixel array based fringe pattern generation method, such as DLP and LCOS, the generation method can
produce higher performance fringe pattern, which is high contrast, narrow pitch and long depth. In this paper, we also
did a contrast between different fringe pattern generation methods.
A high-speed full-field profilometry with coded laser strips projection
Show abstract
Line structure light measurement needs accurate mechanical movement device and high -frame-rate camera, which is
difficult to realize. We propose a high-speed full-field profilometry to solve these difficult ies, using coded laser strips
projected by a MEMS scanning mirror. The mirror could take place of the mechanical movement device with its high
speed and accurate. Besides, a method with gray code and color code is used to decrease the frames number of projection,
retaining the advantage of line structure light measurement. In the experiment, we use a laser MEMS scanner and two
color cameras. The laser MEMS scanner projects coded stripes, with two color cameras collecting the modulated pattern
on the measured object. The color cameras compose a stereo vision system so that the three-dimensional data is
reconstructed according to triangulation.
A hybrid structured-light measurement using a laser projector
Show abstract
The Fringe Projection System (FPS) and the Laser Stripe Projection System (LSPS) both have the limitations in 3D
measurements. For a shiny and diffusive surface with complex shape, neither of the systems could manage it individually
at a low cost. To overcome these difficulties, we propose a method combining these two ways of projections together
using a laser projector, which could project fringe patterns and scanning-laser-stripes both. In this method, we obtain two
disparity maps and two quality maps by FPS and LSPS, respectively. Then combine two disparity maps together by
quality maps and reconstruct the surface of the object with the combined disparity map. Real experiments are carried out
to verify the proposed method and to evaluate the system performance. The plain, the colored and the metal plastic
mixed objects are all reconstructed successfully in the proposed method.