This PDF file contains the front matter associated with SPIE Proceedings Volume 8082, including the Title Page, Copyright information, Table of Contents,Introduction, and Conference Committee listing.

Optical inspection systems constitute hardware components (e.g. measurement sensors, lighting systems, positioning systems etc.) and software components (system calibration techniques, image processing algorithms for defect detection and classification, data fusion, etc.). Given an inspection task choosing the most suitable components is not a trivial process and requires expert knowledge. For multiscale measurement systems, the optimization of the measurement system is an unsolved problem even for human experts. In this contribution we propose two assistant systems (hardware assistant and software assistant), which help in choosing the most suitable components depending on the task considering the properties of the object (e.g. material, surface roughness, etc.) and the defects (e.g. defect types, dimensions, etc.). The hardware assistant system uses general rules of thumb, sensor models/simulations and stored expert knowledge to specify the sensors along with their parameters and the hierarchy (if necessary) in a multiscale measurement system. The software assistant system then simulates many measurements with all possible defect types for the chosen sensors. Artificial neural networks (ANN) are used for pre-selection and genetic algorithms are used for finer selection of the defect detection algorithms along with their optimized parameters. In this contribution we will show the general architecture of the assistant system and results obtained for the detection of typical defects on technical surfaces in the micro-scale using a multiscale measurement system.

Due to the development and progress in micro- and nanotechnology the range of measuring tasks is becoming ever more varied and multifaceted. Decreasing structure widths in combination with large area measurements or complex 3D-micro- and nanostructures with high aspect ratios not only on flat but also on curved surfaces are some of these measurement challenges. In order to solve the problems arising within this application spectrum a multi-sensor platform based on a laser focus probe was developed. This platform is integrated in the Nanopositioning and Nanomeasuring Machine developed mainly at the Institute of Process Measurement and Sensor Technology at the Ilmenau University of Technology with a measuring range of 25 mm x 25 mm x 5 mm and subnanometre resolution.

In manufacturing monitoring and inspection is an essential task to maintain a high product quality. Therefore a variety of systems (e.g. tactile systems, acoustic systems, optical systems,...) is used. However there is still a lack in controlling the product quality near the production machine. For the selection and the design of an appropriate monitoring strategy the specification of the applied sensors is of crucial importance. Optical sensors are in general suitable to measure quality relevant features. But they are often not robust enough, to use them in harsh environments such as the workshop floor. However to detect as early as possible if quality runs out off specification, the high resolution of optical measurement systems is often not needed. In these cases optical sensors can be implemented successfully even if their measurement uncertainty is increasing due to the harsh environment. To verify this hypothesis an evaluation of environmental influences has to be made and a comparison between the acceptable and still achieveable measurement uncertainty has to be made. For this reason a conceptual consideration regarding optical sensors developed for in-process monitoring is presented. The focus will be on the investigation of the influence of the environment on the measurement result, and on strategies how these can be estimated. Based on this an appropriate design and construction of the sensor system can be obtained.

This paper presents a detailed analysis of figures of merit to compare digital Fresnel holography and speckle interferometry. The analysis is based on both theoretical and experimental analyses. A theoretical analysis of the influence of the aperture and lens in the case of speckle interferometry is developed. Compared to digital Fresnel holography, this element is a critical point influencing Shannon conditions, spatial resolution, spatial filtering and photometric efficiency. Optimal filtering and image recovering conditions are thus established. The theoretical analysis is validated by experimental results. The influence of the speckle decorrelation is estimated for the measurement of mechanical deformations. The same mechanical loading has been applied for both experimental configurations. The probability density of the noise map is then estimated. Fitting the curves along the theoretical analysis results in an objective comparison of the decorrelation degrees, and gives keys to compare the decorrelation sensitivity of the methods.

In this publication an experimental configuration for Digital Holography is presented which allows for a modification of the reference wave. Using a reflective liquid crystal Spatial Light Modulator (SLM) placed in the reference arm. The benefit of this approach is demonstrated by applying it to Digital Lensless Fourier Holography. As the optimal configuration of the reference wave depends on the position of the object under investigation, we use the approach to electronically adapt the reference wave to varying positions of the object along and perpendicular to the optical axis and without the requirement of mechanically moving parts.

Quantitative holographic phase contrast imaging enables high-resolution inspection of reflective surfaces and technical phase specimen as well as the minimally invasive analysis of living cells. However, a drawback of many experimental arrangements is the requirement for a separate reference wave which results in a phase stability decrease and the demand for a precise adjustment of the intensity ratio between object and reference wave. Thus, a self interference digital holographic microscopy (DHM) approach was explored which only requires a single object illumination wave. Due to the Michelson interferometer design of the proposed setup two wave fronts with an almost identical curvature are superimposed. This results in a nearly ideal pattern of spatial off-axis carrier fringes and a constant interferogram contrast in the hologram plane. Moreover, the hologram evaluation with spatial phase shifting reconstruction algorithms and Fourier transformation-based spatial filtering methods as well as the integration of DHM in common research microscopes is simplified. Furthermore, the use of laser light sources with a short coherence length is enabled. The applicability of the proposed self interference principle is illustrated by data from the analysis of technical and biological phase specimens. The obtained results demonstrate that the method prospects to be a versatile tool for quantitative phase contrast imaging.

In this paper, we propose and demonstrate Stokes holography for recording and reconstructing a object using polarization fringes. Reconstruction is carried out by scattering the polarization fringes through ground glass, and replacing the ensemble averages by space averages of the randomly scattered Gaussian field. Object encoded into polarization fringes are reconstructed into their corresponding elements of generalized Stokes parameters. Experimental and numerical results of a point object reconstruction are presented.

Searching and recovering the correct reconstruction distance in digital holography can be a cumbersome and subjective procedure. Here we show an algorithm for the automatically estimating the in-focus image and recovering the correct reconstruction distance for speckle holograms. We have tested the approach in determining the reconstruction distances of stretched digital holograms. Stretching a hologram with a variable elongation parameter gives us the possibility to change the in-focus distance of the reconstructed image. In this way, the proposed algorithm can be verified at different distances by dispensing the recording of different holograms. Experimental results are shown with the aim to demonstrate the usefulness of the proposed method and a comparative analysis has been performed with respect to other existing algorithms developed for digital holography.

We present a method capable to improve the resolution limit of an imaging system in digital lensless Fourier holographic configuration. The method is based on angular- and time-multiplexing of the object's spatial frequency information. On one hand, angular multiplexing is implemented by using tilted beam illumination to get access to high order spectral frequency bands of the of the object's spectrum. And, on the other hand, time multiplexing is needed to cover different directions at the spatial frequency domain. This combination of angular- and time- multiplexing in addition with holographic recording allows the complex amplitude recovery of a set of elementary apertures covering different portions of the object's spectrum. Finally, the expanded synthetic aperture (SA) is generated by coherent addition of the set of recovered elementary apertures. Such SA expands up the cut-off frequency limit of the imaging system and allows getting a superresolved image of the input object. Moreover, if a priori knowledge about the input object is available, customized SA shaping is possible by considering the addition of those elementary apertures corresponding with only the directions of interest and, thus, reducing the whole consuming time of the approach. We present experimental results in concordance with theoretical predictions for two different resolution test objects, for different SA shapes, and considering different resolution gain factors.

In order to measure the shape of a large number of identical components in a manufacturing industry we propose a method where digital holography is used to capture an image of the object and then the shape of the object is achieved by using information from the CAD-model. The holographic recording of the object is done using dual wavelengths giving a synthetic wavelength of about 400 μm. This gives a phase map where the phase intervals represent a depth distance on the object of about 0.2 mm. To find the shape of the object the phase map has to be unwrapped. Since the surface contains discontinuities we use information from the CAD-model of the measured object and unwrap the phase iteratively. The result becomes a digital point representation of the measured surface that can either be used just as a description of the object shape or as a way to describe how well the object has been manufactured compared to the CAD-model. The measurement process that is proposed is adapted for on-line purposes; hence it is fast and reliable.

In this work we show several acquisition setups and techniques which make it possible to obtain holographic recording and reconstruction of large objects by means of Infrared Digital Holography (IDH). In previous works it was demonstrated that, using the long wavelength coherent radiation produced by a CO₂ laser instead of visible radiation, it is possible to obtain advantages in terms of larger field of view and lower seismic noise sensitivity. The only drawback using this wavelength is represented by the low resolution of current recording devices in this spectral region. The reported methods may have industrial applications where investigation of large dimension samples is needed.

Advances in information technology open up the potential of combining optical systems with net based infrastructures, allowing for remote inspection and virtual metrology. In this paper, we report our recent work on building a remote laboratory for digital holographic metrology. We describe the architecture and the techniques involved in setting up the remote controlling metrology system. Further consideration will be given to the integration into an advanced infrastructure for remote experimentation, data storage and publication. Some other important issues such as information security will not be addressed.

A measurement prototype based on digital holography for the simultaneous measurement of out-of-plane and radial in-plane displacement fields is shown. This prototype enables recording two holograms at the same time with a single image taken by a digital camera and evaluating separately in-plane and out-of-plane displacement components. An axicon-type diffractive optical element (DOE) is used for the illumination of the object, which causes radial sensitivity vectors. Blind holes as well as spherical indentations were preformed over a welded steel plate (containing residual stresses). By using the digital holography setup, typical out-of-plane and in-plane displacement fields, generated when the hole was introduced into the stresses material, were measured and compared with theoretical ones. Good agreement was found between them. In addition, a mature digital speckle pattern interferometry (DSPI) setup was used to measure only the in-plane component around the hole. Good agreement between both systems was also found. Finally, displacements fields were measured around indentation marks. In this case, preliminary results show that out-of-plane displacements are larger than in-plane ones, enabling its use for residual stress computation or maybe material properties determination.

In this paper we start by presenting one recent development in the field of geometric super resolution. The new approach overcomes the reduction of resolution caused by the non ideal sampling of the image done by the spatial averaging of each pixel of the sampling array. Right after, we demonstrate a remote super sensing technique allowing monitoring, from a distance, the heart beats, blood pulse pressure and the glucose level in the blood stream of a patient by tracking the trajectory of secondary speckle patterns reflected from the skin of the wrist or from the sclera.

To use flip chip interconnection technology for semiconductor packages offers a number of possible advantages to the user: reduced signal inductance, reduced power/ground inductance, higher signal density, die shrink, and reduced package footprint. However, manufacturing processes for 'flip chip'-integrated packages need a high precision alignment between flip chip and matched substrate. Comparing with original visual alignment based on 2D image information, an advanced die placement inspection system for reliable flip chip interconnections has been firstly proposed by authors [2]. In this paper, the proposed system is reviewed briefly, and system calibration algorithms and information processing algorithms are described in detail. To verify the system performance, a series of real experiments is performed on flip chip packages for high performance computing, and its results are discussed in detail.

Semiconductor device packaging technology is rapidly advancing, in response to the demand for thinner and smaller electronic devices. Three-dimensional chip/wafer stacking that uses through-silicon vias (TSV) is a key technical focus area, and the continuous development of this novel technology has created a need for non-contact characterization. Many of these challenges are novel to the industry due to the relatively large variety of via sizes and density, and new processes such as wafer thinning and stacked wafer bonding. This paper summarizes the developing metrology that has been used during via-middle & via-last TSV process development at EOL/ITRI. While there is a variety of metrology and inspection applications for 3D interconnect processing, the main topics covered here are via CD/depth measurement, thinned wafer inspection and wafer warpage measurement.

Photolithography is the key technology of the chip production in semiconductor industry. Increasing demands on wafer overlay requirements lead to increasing demands on registration accuracy of photomasks. The PROVE^TM photomask registration metrology tool has been developed by Carl Zeiss SMS to address the need for high imaging resolution in combination with excellent measurement performance. This paper reports the current status of PROVE™, highlighting its optical performance and correction algorithms. The tool is designed for 193 nm illumination and imaging optics, which enables at-wavelength metrology for current and future photomask manufacturing requirements. Registration and line width metrology is offered by the optical beam path using transmitted or reflected light. The opportunity of selecting optimized illuminations allows a smart adaption of the tool to the measurement task. The short wavelength together with a numerical aperture of 0.6 allows sufficient resolution down to the 32 nm manufacturing technology requirements. The stable hardware platform and the newly developed PROVE™ high precision optics enable a short term repeatability of less than 0.5 nm (3sigma). Distortion can be calibrated by using advanced image analysis and self calibration methods. The optical correction of the entire field of view delivers the requested screen linearity of less than 1 nm. It is shown, that the calculated optics correction is valid for different structure types and all kind of illuminations.

To decrease the effort to detect micromechanical features by touch probe measuring systems, multiple touch probes composed in an array are used to measure some of these structures at the same time, owing to the alignment of many similar structures on a wafer. While usually the touch probe signal is read out electronically, in this investigation a Shack-Hartmann sensor is used to observe the reflective back plane of the micro probe array. Shack-Hartmann wave-front sensors use microlens arrays in conjunction with a CCD array. A planar wave-front that is transmitted through a microlens array and imaged on a CCD sensor will form a regular pattern of bright spots. If, however, the wave-front is distorted, the light imaged on the CCD sensor will consist of some regularly spaced spots mixed with displaced spots and missing spots. This information is used to calculate the shape of the wave-front that was incident on the microlens array.

A novel iterative phase-retrieval algorithm is developed for reconstruction of phase objects. We propose a constrained variational formulation of the phase-retrieval problem with the forward wave field propagation from the object to the measurement planes as constraints. It is assumed that noisy intensity-only observations are given at measurement planes parallel to the object plane, and the additive noise in the observations is zero-mean Gaussian. This algorithm is derived from the maximum likelihood approach what enables an optimal solution for the phase reconstruction. The advanced performance of the algorithm is demonstrated by numerical simulations.

Recently we have proposed the conception of an innovative experimental scheme for phase retrieval from a set of consecutive intensity measurements. It is based on a 4f-optical filter with a reflective phase-only spatial light modulator (SLM) located in the Fourier domain. The main advantage of this scheme is the greatly reduced measurement time since no mechanical shift is required throughout the capturing process. To recover the phase, the captured intensities have been subjected to an iterative process based on generalized projections. Here, we investigate the influence of misalignment, between the optical axes of the setup, on the performance of the iterative scheme's solution. It is demonstrated that if misalignments is present, measurement errors will be propagated in the iterative process and thus affect the accuracy and the rate of convergence of the phase retrieval. The concept is demonstrated by investigating the wavefield diffracted by the U.S. Air Force resolution target. In the case of an aligned setup, it is shown that only 5 planes and 10 iterations give good reconstructions.

The transport-of-intensity equation (TIE) describes a deterministic relation between the intensity distribution in different focal planes and the corresponding phase distribution. A Green's function solution of the TIE is used to retrieve the phase distribution of an object considering specific boundary conditions. This leads to an accurate reconstruction of the properties of phase objects, e.g. the refractive indices and thus the numerical aperture (NA) of optical fibers. The required intensity distributions are captured simultaneously by the use of a multi-camera microscope. The TIE is solved using a computer algorithm, which can be massively parallelized. This offers the application of general purpose computation on graphics processing units (GPGPU). Therefore real-time reconstruction of the phase distribution is possible.

In many practical microscopy applications the use of phase information is crucial. In this contribution we propose a method for phase extraction in a microscopy system based on analysis of images with varying defocusing. The system has no mobile parts owing to the defocusing by means of a spatial light modulator. The base of the method is the captre of images in a microscope with varying tube lens focal lengths. This produce a set of intensity images, all of them related, because the can be generated by free space propagation of a complex distribution which is unknown.

A vibration-insensitive interferometer with simple structure is proposed. Under normal incidence, both the reflection phase and magnitude of the thin film at different wavelengths were measured and utilized to calculate refractive index and thickness of the thin film. The experiment results showed the precisions were obviously increased after the phase measurements were added into analysis.

The assessment of surface finish has become increasingly important in the field of precision engineering. Optical interferometry has been widely used for surface measurement due to the advantages of non-contact and high accuracy interrogation. In spite of the 2π; phase ambiguity that can limit the measurement scale in monochromatic interferometry, other optical interferomtry have succeeded to overcome this problem and to measure both rough and smooth surfaces such as white light interferometry and wavelength scanning interferometry (WSI). The WSI can be used to measure large discontinuous surface profiles by producing phase shifts without any mechanical scanning process. Where the WSI produces the phase shifts by altering the wavelength of a broadband light source and capturing the produced interferograms by a CCD. This paper introduces an optical setup and operation principle of a WSI that used a halogen white light as a broadband illumination source and an acousto-optic tunable filter (AOTF) as a wavelength scanning device. This setup can provide a wide scan range in the visible region. The scanned range is being operated from 682.8 nm to 552.8nm and the number of captured frames is 128. Furthermore, the obtained interferograms from a Linnik interferometer have been analyzed by two methods, Fast Fourier Transform and Convolution. A mathematical description of both methods is presented then a comparison in results accuracy is made between them. The Areal measurement of a standard 4.707μm step height sample shows that FFT and convolution methods could provide a nanometer measurement resolution for the surface finish inspection.

We propose a technique for monochromatic laser interferometry capable of absolute surface profilometry of an object with large height gaps exceeding a half wavelength. The technique does not use a broadband source, such as a low-coherence or multi-wavelength source, or a wavelength-tunable device, which causes a dispersion problem. Instead, we make use of the phase change of monochromatic light through the angular shift of illumination introduced by tilting the optical axis of the interferometer. For oblique illumination at angle θ, the phase difference between the test and reference surfaces separated by distance d is given by ΔΦ = 2kd cosθ , where k = 2π /λ is a wavenumber. In effect, the change of illumination angle θ functions as the change of wavelength λ . Therefore, while using a monochromatic laser light source, we can realize the same effect as a multi-wavelength source. From the relation between the illumination angle and the phase change, the absolute distance d between the test and reference surfaces can be determined without ambiguity of an integer multiple of a half wavelength associated with monochromatic interferometry. The large gap height can be determined also without ambiguity from the change of the absolute distance d across the boundary of the gap. Because the resolution of the absolute distance measurement by means of illumination angle change is not high enough by itself, we enhance the resolution by the following procedure. We first estimate the gap height to an integer multiple of a half wavelength by tilting the optical axis. Then the fractional portion of the phase is measured by setting the optical axis perpendicular to the test surface as in conventional interferometry. By combining the integer and the fractional portion, we can determine the absolute gap height with high accuracy and a large dynamic range exceeding a half wavelength. We present an experimental demonstration with a traditional Twyman-Green interferometer, in which a He-Ne laser was used as a monochromatic light source, and a test surface with a ~0.1 mm height gap was formed by two block gauges attached to a flat surface. The repeatability for five measurements was found to be as high as 0.1nm (in 1 sigma).

Structured-illumination microscopy is an incoherent method to measure the microtopography of rough and smooth objects. The principle: A sinusoidal fringe pattern is projected into the focal plane of a microscope. While the object is scanned axially, the contrast evaluation of the observed pattern delivers the 3D topography with a height uncertainty of only a few nanometers. By means of a high aperture the system can measure steep slopes: +/- 50 degrees on smooth objects (NA=0.8) and +/- 80 degrees on rough surfaces are possible. For industrial applications a fast measurement is one of the most desired aspects. We face this demand by exploiting the physical and information-theoretical limits of the sensor, and giving rules for a trade-off between accuracy and efficiency. We further present a new method for data acquisition and evaluation which allows for a fast mechanical scanning without "stop-and-go".

Chromatic dispersion of polarization modes in holey fibers is measured over a broad spectral range (e.g. 500-1600 nm) using two white-light spectral interferometric techniques. First, a technique employing an unbalanced Mach-Zehnder interferometer with a fiber in the test arm is used to measure the wavelength dependence of the differential group effective index, or equivalently the chromatic dispersion of one polarization mode supported by the fiber. Second, a technique employing a tandem configuration of a Michelson interferometer and the optical fiber under test is used to measure the group modal birefringence in the fiber. From these measurements, the chromatic dispersion of the other polarization mode supported by the fiber is retrieved. We measured by these techniques the chromatic dispersion of polarization modes in four air-silica holey fibers and revealed the dependence of zero-dispersion wavelength on the geometry of the holey fiber.

Multi-wire sawing of silicon wafers is a tribological process. Slurry consisting of small silicon carbide particles embedded in polyethyleneglycol carries out the abrasive material removal process. During this process small silicon chips are removed from the bulk material. Low coherence interferometry (LCI) is widely used for high accuracy surface topography measurements of materials. This paper presents an application of LCI where the surface of a material (silicon) is inspected from the inside. Light in the near infrared (NIR) wavelength region is used. High spatial resolution is necessary to be able to observe the processes on the micro scale. Therefore a modified solid immersion approach is suggested. That makes it possible to reach a spatial resolution in the range of the illumination wavelength. The topography changes produced by the chippings are in the range of some micrometers. To be able to estimate the volumes of the Si chippings interferometric phase measurements are applied.

Coherence scanning interferometry CSI with a broadband light source (short known as white light interferometry) is, beside the confocal technique, one of the most popular optical principles to measure surface topography. Compared to coherent interferometry, the broadband light source leads, theoretically, to an unambiguous phase information. The paper describes the properties of the correlogram in the spatial and in the frequency domain. All deviations from the ideal correlogram are expressed by an addition phase term. The uncertainty of height information is discussed for both, the frequency domain analyse (FDA) proposed by de Groot and the Hilbert transform. For the frequency domain analyse, the uncertainty is quantified by the Cramér-Rao bound. The second part of the paper deals with the phase evaluation of the correlogram, which is necessary to achieve a high vertical resolution. Because the envelope function is often distorted, phase jumps lead to ambiguous height informations. In particular, this effect can be observed measuring rough surfaces.

The precise and fast acquisition of three-dimensional geometrical data of micro-components is mainly performed by two alternative measuring techniques, either vertical scanning white-light interferometry (SWLI) or confocal microscopy. Both are capable of measuring micro-structured surfaces with a very high precision while recording image sequences during a so-called depth scan. For most applications the axial resolution of these systems is sufficient. Though, in certain applications the lateral resolution of a measurement system is far more critical. In addition, there are several approaches to define the lateral resolution in 3D microscopy. In this paper, we discuss some physical approaches to improve lateral resolution and transfer characteristics in SWLI. As a contribution to the EC-funded project "NanoCMM" we developed a special kind of Linnik white-light interferometer, which provides a lateral resolution well below one micrometer even for working distances of more than 5 mm. The resolution enhancement was achieved by wavelength reduction, i.e. LEDs emitting in the blue and near UV range were used for illumination. We compare the results obtained from a silicon pitch standard based on different illumination sources with a conventional Mirau interferometer providing the same magnification. Finally, in another setup we show that the batwing effect can be successfully reduced by using a confocal aperture in the illumination path of the interferometer. The combination of these different modifications clearly improves SWLI measurement results in comparison with those performed by conventional white-light interferometers.

Industry rely a lot on vision for in line or off line quality inspection. Whereas most of these applications use 2D vision, the need for 3D vision is increasing. Optical Coherence Tomography (OCT) is widely used in medical application to obtain 3D images of biological tissues but is still limited to low-speed and high price instruments in industrial applications. We developed a CMOS camera specially designed for parallel OCT (p-OCT). The advantage of this method over other OCT techniques is its high speed and its ability to maintain a high lateral resolution over large measurement depths. Our camera can acquire up to one million 2D images per second. The amplitude and phase of the modulated signal is calculated within every pixel. Up to 10'000 such amplitude and phase results can be returned in a second, for every pixel. We will present our instrument, which includes a rugged and compact interferometer aligned with a robotized assembly technique. This imaging interferometer is scanned during acquisition, allowing to maintain a high lateral resolution (typically 2 micron) over several millimeters. The interferometer is easily interchangeable (snap-in magnets) in order to choose the ideal magnification for the application. This compact and versatile system can be built directly on a robot arm or scanned over large objects.

Fringe projection techniques have been widely used for inspection of free form surfaces for quality inspection or reverse engineering purposes. For inline 3D-inspection systems maximum measuring speed is of vital interest. Typically, image acquisition and processing rates of up to 10'000 frames/s are state of the art. In order to exceed this value, we propose a fringe projection concept which uses a high speed CMOS camera with in pixel phase calculation. The camera can record up to 1 million frames/s. An analogue calculation is realized in every pixel to extract the phase of the temporarily modulated light. In order to determine a phase, the illumination light must be modulated with a quarter of the frame rate of the image acquisition device, in our case with up to 250 kHz. In fringe projection techniques, the projected fringes must be shifted with respect to the inspected surface. Mechanical phase shifting of the fringes becomes the crucial problem in ultra high speed fringe projection. We have investigated a new way to generate 250 kHz phase shifted fringes. In this paper, we present the new fringe projection technique and discuss the results of our high speed 3D measuring device.

The precise shape measurement of fast rotating objects is a challenging task in metrology. Deformation measurements of lightweight composite materials are important to guarantee its robustness e.g. against impacts since they cannot be simulated reliably. In a high-speed rotor test rig, their elastic and plastic deformations due to centrifugal forces can be evaluated. Non-contact inspection techniques with micron resolution under vacuum conditions are necessary. We present for the first time deformation measurements of a high-speed cylindrical rotor by a non-incremental interferometric array sensor system. Rugged compact sensors were realised by employing optical fibers and diffractive optics. Unique is the determination of the radial expansion also in the presence of an unsteady tumbling motion of the rotor which is also monitored.

Achieving real time 3D measurement of microscopic surfaces is difficult, mainly because of the high bandwidths required for the data acquisition by the probe or camera, the transfer to the processor and the processing. In this paper we present the results of our second prototype on-line measurement system that we have developed using continuous scanning white light interference microscopy, a high speed CMOS camera and parallel processing with an FPGA that enables data processing rates of up to 160 Mb/s. Two fringe detection algorithms have been implemented, one based on the detection of the maximum fringe intensity and the other on the maximum of the fringe modulation function. The practical performance is demonstrated on the measurement of laterally translating samples, with 3D image rates of up to 20 i/s being achieved for an image size of 256 x 320 pixels, and 2.96 i/s for an image size of 640 x 1024 pixels over a depth of 5 μm. Depths of up to 20 μm can be measured. On-line 4D microscopy opens up new applications for characterizing surfaces that are moving or changing in a non-periodic way with time, such as in MEMS, soft materials, layer growth or chemical reactions.

In micro manufacturing (MEMS, polymer hot-embossing, polymer roll-to-roll imprint, etc.) precise micro and nano-sized features are distributed over large areas. In order to inspect for defects or employ statistical process control on micromanufactured parts, metrological instruments must collect data with submicron resolution at a rate fast enough to keep up with the pace of production. Commercial inspection instruments fall short on meeting these challenging demands. In this paper we detail the design, implementation, and results of an optical system build to provide real-time inspection for transparent polymer microfluidic devices. Our current hardware demonstrates 0.5 micron lateral resolution with 1 micron vertical resolution at a rate of 640,000 voxels per second. Furthermore we demonstrate the ability to measure vertical sidewalls. The tilted orientation of our camera system provides access to these typically hidden or eclipsed areas. We conclude the paper with a direct comparison of our instrument's capabilities against a white light interferometer and laser scanning profilometer. The data demonstrates the difference between the instruments' lateral and vertical resolution, data acquisition rate, and vertical sidewall measurement capabilities.

A sensor based on fringe projection technique was developed which allows ultrafast measurements of the surface of flat measuring objects which realizes a data acquisition rate up to 8.9 million 3D points per second. The high measuring velocity was achieved by consequent fringe code reduction and parallel data processing. Fringe sequence length was reduced using geometric constraints of the sensor arrangement including epipolar geometry. Further reduction of the image sequence length was obtained by omission of the Gray code sequence by using the geometric constraints of the measuring objects. The sensor may be used e.g. for inspection of conductor boards.

At the Physikalisch-Technische Bundesanstalt (PTB) two new scanning deflectometric systems (Deflectometric Flatness Reference: DFR) were installed for measuring topographies of nearly flat surfaces with sub-nanometre uncertainty. The two systems can measure the form of horizontally and vertically orientated specimens with a diameter of up to 700 mm. The systems are based on different deflectometric procedures, the so-called direct and the difference deflectometry. With the flatness measuring systems, an uncertainty down to 0.1 nm (depending on the specimen and its peak-to-valley) is being aimed at for the 95% coverage interval. Virtual experiments show that the optical and mechanical components must be aligned in the arcsecond range in order to achieve errors for the topography in the sub-nanometre range. In this paper we describe the setup of the new DFR system for horizontally orientated specimens in detail and show methods and experimental results for an accurate alignment of the optical and mechanical components. We present an accurate alignment strategy for ultraprecise deflectometric measurements and show a measurement of a section at a horizontally orientated specimen.

This paper describes an optical device that uses a new configuration of a technique known as deflectometry applied to ballistic identification. The main novelty is characterized by the use of a 45° conical mirror to measure the near cylindrical surface of the bullet. deflectometry is an optical technique sensitive to variations in topography and unevenness of a surface. This technique allows to identify and to measure the geometry of objects based on the distortions observed in a sequence of image patterns reflected on the surface of interest. The measurement by deflectometry is very sensitive to the surface local gradients and curvatures. In this paper it is applied to forensic ballistic in order to verify if a given bullet could be fired by a suspect weapon. Comparisons between images of bullets fired by the same weapon were made.

Within the scope of the Collaborative Research Centre (CRC) Transregio 73 (SFB/TR73) research project, a new kind of micro fringe projection system is being developed. By using flexible imaging fibre bundles, it becomes possible to collect complete data sets of filigree and hardly accessible assembly geometries. The talk presents the principle of the new kind of endoscopic micro fringe projection system and points out its certain advantages. It combines a laser light source with a Digital Mirror Device (DMD), image fiber and advanced micro optics. Thereby a 7.5 times increased depth of focus of 3 mm compared to 0.4 mm with common light sources could be achieved. Preliminary considerations of the optical design, simulation results and the consequential setup are as well shown as measurement results of the current system.

Industrial optical 3D-measurement techniques are well established to achieve quality targets in production and manufacturing. However measurements inside of objects, especially small ones, are still a challenge since there is no easy access for measurement tools. Inspection tools like endoscopes, which provide a 2D-view or a stereoscopic view of inner surfaces, are commercially available and widely used. Nevertheless, there is no technique for precisely measuring the inner surface geometry of a small hollow object. Especially medical applications would greatly benefit from "dimensional" measuring. Thus a novel approach and a corresponding prototype of a miniaturized endoscopic 3D-scanner are presented. To be suited even for very narrow objects, the prototype has a maximum diameter of 3.6 mm, its flexible design allows for access to bent tubes or canals. The 3D scanning approach is based on the principle of active triangulation, which means that a coded light pattern is projected and then viewed under a different angle. It is usually difficult to realize triangulation setups in a small embodiment. Therefore an optical tandem of a miniaturized pattern projector and a small camera with a resolution of 400 x 400 pixel is presented as a practical solution. The projector projects a pattern of 15 rings of distinct colors into a cylindrical measurement space where the color sequence constitutes a code. The camera uses a catadioptric setup with a spherical mirror to enhance its field of view. It detects the projected rings and is then able to unambiguously reconstruct the 3D-shape of a surface using ray-cone intersection. This so called color coding approach provides several advantages. For example, only a static projection pattern is needed, which greatly reduces complexity and size of the projector compared to phase shifting technologies. Experimental 3D-scans of arbitrarily shaped tubes demonstrate good performance and an accuracy of about 0.1mm.

In three dimensional (3D) shape measurement based on fringe projection, a serial of well designed color strips is used to encode each period of the projected sinusoidal fringe. It is considered one of the most reliable techniques for recovering 3D shape of a tested objects, even with spatially isolated surface. The sinusoidal fringe intensity is used to extract the phase information of the tested object, and the color strips with known order is assisted to recover its corresponding natural phase distribution. Principles of this technique and three color encoding methods with difference color codification are described in this paper. Some experimental results are also presented. In each method, each fringe order only depends on its own corresponding color information, has nothing to do with the neighborhood fringes in space, thus, unwrapping error is limited in a small area and won't expand to other pixels. It takes great convenience for 3D measurement of an object with spatially isolated surface. With only one image, 3D shape of the tested object can be exactly reconstructed, thus the speed is limited only by the frame rate of camera, so these methods can also be used in 3D shape measurement for dynamic object.

In the paper a new approach for two step calibration process allowing 3D measurement in large volumes is presented. The maximum assumed volume is equal to 20m x 15m x 6m and the developed system is portable and easy to operate by one person. To set-up a traditional 3D structured light system a long enough base distance between projector and detector is required to ensure sufficient measurement sensitivity. In this setup to achieve measurement uncertainty in the range of 20mm the minimum 10m base distance is required. For this base distance it is nearly impossible to set-up a rigid frame for fixing projector-detector configuration and allow to anyone for easy manipulation of such system. Taking into consideration the above mentioned requirements a new calibration method has been proposed. Its main assumption is that there is no requirement for fixing projector and detector during a calibration phase. The relation between projector and detector is established just before measurement where they are finally positioned to capture 3D shape of investigated surface. It works in two steps: the first one is based on independent calibration of projector and detector devices to establish relation between their the pixel (i, j) co-ordinates and lines in free space; the second one is based on a set of measurements of a known calibration model and their analysis allowing calculation of a relative transformation between detector and projector co-ordinate spaces. The first step is always done in laboratory and the second one is performed just after any change in a relative position between projector and detector. In the paper the initial assessment of measurement uncertainty is discussed in relation to the calibration model versus a measurement volume size. Also some exemplary measurements of real engineering structures will be presented and functionality of the system are discussed.

3D measurement setups based on structured light projection are widely used for many industrial applications. Due to intense research in the past the accuracy is comparably high in connection with relatively low cost of the equipment. But facing higher acquisition rates in industries especially for chain assembling lines there are still hurdles to take when accelerating 3D measurements and at the same time retaining accuracies. We developed a projection technique that uses laser speckles to enable fast 3D measurements with statistically structured light patterns. In combination with a temporal correlation technique dense and accurate 3D reconstructions at nearly video rate can be achieved.

A portable optical measurement system, capable of measuring free form surfaces over large areas and comparing them with reference surfaces was developed within this work. The system merges passive and active stereo vision. Data is acquired in both modes for each partial overlapped position of the system, covering all the area of interest of the free form surface or part being measured. In passive stereo vision mode, circular targets are used to determine the coarse position of the system (i.e. cameras and projector) referenced to a global coordinate system defined by the targets. In active stereo vision mode, three-dimensional point clouds are locally measured and registered in the global coordinate system. The algorithm performs the calculation of these point clouds into a single intrinsically structured regular mesh, allowing an efficient comparison between different surfaces because the correspondence of points can be pre-defined. Experimental evaluations, using different kinds of geometric patterns and calibrated free form surfaces demonstrate the feasibility and the advantages of the proposed methods.

Fringe projection systems can be used for the measurement of complex workpiece geometries. Virtual fringe projection systems can be used for the calculation of optimal measurement strategies with respect to criteria like a minimal measurement uncertainty. This is the main field of research of the subproject B5 of the collaborative research centre 489 (CRC 489), funded by the German Research Foundation (DFG). The main task of the subproject is to develop a virtual multisensor assistance system for the calculation of workpiece adapted measurement strategies. This paper focuses on the model and calibration of the used fringe projection sensor. The sensor has to be modelled and the system parameters have to be identified by an accurate calibration procedure. The used fringe projection system has a camera lens with an object-sided telecentricity. Usually, the components projector and camera were described using a pinhole model, which does not reflect the telecentricity. This means, that the existing physical formulations and calibration procedures cannot be used, here. In this paper, the model and calibration strategy for the calculation of the system parameters are described in detail. In order to get a precise simulation model, each intrinsic and extrinsic parameter is considered. To verify the virtual model and the calibration strategy, the calibration was repeated and the standard deviation of the parameters was calculated. Furthermore an optical flat and a groove artefact will be measured and the planarity of the optical flat and the depth of the groove artefact will be determined and compared to the calibrated values.

Interferometry is often used to measure the form of optical surfaces. While interferometry is generally expected to give high accuracy results, a variety of error influences exist which have to be considered. Some typical error influences which are often underestimated will be discussed in this paper. In flatness metrology, the main error influences are imperfections of the reference surfaces, specimen support or cavity influences. For non-flat surfaces like aspheres or free form surfaces, in particular the influence of errors from the determination of the lateral coordinates becomes very important. Sub-aperture interferometry copes with stitching errors, which can be reduced by Traceable Multi Sensor subaperture methods where the influence of the imaging system of the interferometer may dominate the error budget. This can be similar for other types of interferometers.

A lateral shearing interferometer usually provides the slope data of a wave front under test along one direction. For the complete reconstruction of the wavefront, two slope datasets along different directions are required. Based on diffractive gratings, a simultaneous measurement of bothdata sets can be carried out. Two possible realizations are presented using a polarization signature and a partially coherent light source.

Aspherical surfaces are characterized in reflection using a quadri-wave lateral shearing interferometer (QWLSI). This measures the deformation of a reference source due to the reflection on an aspherical shape. Thanks to the wave front sensor high dynamic range, aspherical sags as large as 100 μm are achieved.

This work presents further insight into the working principles of the tilted-wave interferometer regarding the system characterization for the measurement of aspheres and freeform surfaces. A method to characterize an optical system for the measurement of aspheric and freeform surfaces without dedicated null optics in a non-null measurement fashion is presented. Even though non-null test arrangements allow for increased measurement flexibility the evaluation of the measurement results becomes much more complex than in the null test variant. The problem becomes then the identification of small phase deviations caused by the test surface in the presence of systematic system aberrations several orders of magnitude larger. The characterization of the interferometer aberrations plays hereby a central role in the measurement process for an accurate assessment of the test surface. In this work, a novel method for the characterization of the interferometer setup is described and measurement results in a non-null test configuration for an aspheric element with several hundred waves departure from its best-fit sphere presented.

A subaperture stitching algorithm was developed for testing aspheric surfaces. The full aperture was divided into one central circular region plus several partially-overlapping annuli. Each annulus was composed of partially-overlapping circular subapertures. The phase map in each subaperture was obtained through the phase-shifting interferometry and retrieved by an iterative tilt-immune phase-shifting algorithm and a Zernike-polynomial-based phase-unwrapping process. All subapertures in one annulus were stitched simultaneously in least-squares sense. By eliminating the relative piston and tilt between adjacent subapertures, the sum of squared errors in the overlapped regions was minimized. The phase stitching between annuli also utilized the least-squares method in the overlapped region. Simulation results on a test wavefront with 30-wave spherical aberrations demonstrated the effectiveness of the proposed algorithm. The rms phase residue after the phase-shifting, phase-unwrapping and phase-stitching processes was 0.006 waves, which met the precision requirement of common interferometers. This algorithm should be applicable to general surfaces in subaperture stitching interferometry.

Axicon surfaces are widely used in nowadays optical engineering, requiring accurate metrology for these highly aspheric surfaces. In this contribution, we present a complete approach to determine the shape deviation of axicons in an absolute manner. The setup is an interferometric null configuration using a computer generated hologram (CGH) as null optics. We demonstrate an absolute shifting method and the calibration issues connected with measuring the absolute cone angle. Experimental results are shown for the metrology of a 90° cone angle sample.

A new type of machine setup combining a profilometer with a rotational measuring axis to measure aspheric lenses is presented. The instrument is very flexible, as it does not need a specific hologram for each type of asphere. In general, the setup is also capable to measure freeforms. Metrology strategies and first results are presented.

An experimental ray tracer for measuring the optical aberrations of aspherical lenses is presented. Setup is based on the principle of ray tracing which is used in optical design for virtually tracing rays through an optical system. This method has the potential to be used in aspherical lens testing because of its flexibility and high dynamic range. Wavefront aberrations can be calculated from results of experimental ray tracing. Furthermore the method offers the possibility of retrieval of aspherical surface profiles. Preliminary results with a plano-convex aspherical lens are compared with those obtained by a commercial surface profiler.

An automatic method for the positioning of a test surface in a non-null interferometer is presented. If the test surface is positioned incorrectly with respect to the test beam this leads to aberrations, which distort the measurement of the surface. A central issue in the interferometric characterization of surfaces is to avoid aberrations due to an incorrect placement of the test surface. In case of spherical and plane surfaces these errors can usually be distinguished from the surface figure errors and are eliminated in post processing. For aspheric and free-form surfaces this task is no longer trivial. Therefore it is important to minimize the alignment error of the surface. In this work the effect on the measured phase due to lateral and axial displacements of the aspheric surface is calculated and an adjustment method for the positioning of the surface at a predefined measurement location is presented. Experimental results showing the feasibility of the proposed procedure are presented.

The position of optical surfaces and elements in the final assembly of an optical system has a strong influence on the imaging quality of the system. After the assembly of the complete optics is finished it is difficult to check the centering error and the distances of the single optical elements. We will describe a technique to measure the lateral displacement of each centre or curvature with respect to a given reference axis with 0.1 micron accuracy. Additionally it is possible to measure the distances between surfaces of the assembled optics with an accuracy of 1 micron. The measurement is based on the combination of a focusing autocollimator and a short coherent interferometer. The measurement is non-destructive and can be applied to optical systems with several optical elements (approx. 20 lenses). Both the focusing autocollimator and the short coherent interferometer are working independently. It will be shown that a combination of these methods improves the feasibility and accuracy of both methods. In general the method can be applied to optical systems based on spherical surfaces. As far as the paraxial area is considered, the use of this method can be also extended to systems with aspherical surfaces. The restriction is that these measurements will only provide the information of the lateral displacements of the paraxial centres of curvature and the distances between the optical surfaces. The tilt of the aspherical axis is not revealed by this technique. But with the use of an additional optical distance sensor and a special quality control strategy the tilt of each aspherical axis in the assembled optical system can be determined. The quality strategy requires some preliminary measurements of the single optical elements before assembly. Applications mainly include the measurement of cell phone and digital camera lenses. However, any type of objective lens from endoscope up to very complex objective lenses used in microlithography can be measured with highest accuracy. Measurement results of different samples will be provided and discussed.

In numerous interferometric applications of nanopositioning and nanomeasuring technology, plane mirrors are used as flatness or straightness standards for the movement of a positioning device. During this process, the shape deviations of the mirrors used lead to systematic errors of the position measurements, which can be corrected in later applications if known. Most often the effective shape deviations are described sufficiently well by profile deviations along a profile line which is fixed by the movement of the positioning or measuring device. The novel precision device - a so-called interferometric nanoprofilometer - for measuring the profile deviations of plane mirrors presented in this paper is based on the comparison of the profile line of the mirror to be tested with a straightness standard embodied by a mirror of very high flatness. A specially designed point-based measuring interferometer is moved along the profile line. As the measurement is directly referenced to the straightness standard, the influence of the guide errors was greatly reduced. The uniform movement of the interferometer is ensured through a linear measurement table, which is driven using speed control and pulse-width modulation. Apart from the mechanical and optical design of the interferometric nanoprofilometer, a hardware module was assembled which enables the control of the linear measurement table and the extraction of pulses for the synchronous acquisition of position and profile deviation values. In addition, a software tool was developed for configuring the measurement process and for data recording as well as a program to perform various analyses of the profile deviations. In measurements performed with the interferometric nanoprofilometer covering the maximum scanning length with lx=250 mm under laboratory conditions, the expanded uncertainty was U(l)=7.8 nm at a confidence level of p=95% (k=2).

Ultra high-resolution measurements of amplitude and phase fields emerging from fine period amplitude gratings are presented and discussed. In the axial direction periodically repeated features are found, whose origins are the Talbot effect within the Fresnel diffraction regime. The phase field recording leads to a very precise measurement of the localization of the Talbot planes and precisions below 100 nm are demonstrated. The concept of immersion interference microscopy is demonstrated. By accessing the back focal plane of the observation system filtering of diffraction orders provides specific Talbot images and allows to intuitively understand the role of diffraction orders for Talbot effect.

Interferometric metrology is well established for both single point and full field measurements. However, absolute techniques for long range measurements, spanning 100's to 10,000's of fringe orders whilst maintaining sub-fringe resolution have been reported with widely varying levels of performance. In this paper, techniques for long range multi-wavelength interferometry are reviewed with respect to applications of classical interferometry and fringe projection profilometry. Whilst hierarchical geometric series methods provide a potential solution it is shown that significantly greater freedom in wavelength selection is obtained by applying excess fraction principles and a new predictive model for this technique is discussed.

Phase profiles obtained by phase shifting interferometry often include undesirable concentric ripple-noises, like "bull's-eye patterns" which are caused by scattering from defects on surfaces of optical elements in interferometers. We propose a numerical technique for reducing these bull's-eye noises via numerical diffraction. This technique is applicable to phase data obtained from all types of interferometer, since it only needs the phase data itself. We experimentally demonstrate that this technique is effective in elimination of bull's-eye noises from interferometer data. This technique is applicable to the data obtained from digital holography as well.

Single-camera frame instantaneous interferometry is an alternative optical test method where environmental noise prohibits conventional phase shifting methods. For the most demanding applications, the instrument should have high light efficiency and sufficient source power to accommodate short camera shutter times, effectively freezing object motion. Here we report on a new instantaneous Fizeau-type interferometer with fully coherent optics that provide high light-efficiency and increasing lateral resolution with zoom, and a novel 4mW, stabilized 633 nm laser source for single-shot metrology with exposures as short as 12 microseconds. We illustrate how this instantaneous measurement capability enables continuous live display of surface profiles and Zernike fits, and dynamic data acquisition for recording varying surface profiles or cavity disturbances at a rate of 82 Hz.

A common-path interferometric profilometer using a Savart plate as a lateral shearer has been successfully tested under harsh environmental conditions to measure the shape of a surface, detecting defects and characterizing surface properties. The whole profile is obtained from a single image and its depth sensitivity is easily scalable, making this technique suitable for many different applications. Although this system has been successfully used for surface inspection and defect detection, some behaviors cannot be explained by the usual simple model for fringe formation, which, amongst other things, considers normal incidence of the incoming rays into the Savart plate. These deviations from the ideal case are more noticeable for high resolutions from short distances. This paper studies the formation of the fringe pattern, which is crucial for understanding the behavior of the system and proper calibration.

We propose a simple scheme for accurate state of polarization (SOP) mapping with an interferometric polarimeter using Fourier transform method of fringe analysis. In single shot polarimeters that use Fourier transform method of fringe analysis, a spatial carrier frequency is introduced in the fringes of recorded interferogram either by introducing the relative tilt between the sample beam under test and a reference beam, as demonstrated by Ohtsuka and Oka or by passing the sample beam through birefringent optical components such as Wollaston prisms as demonstrated by Oka and Kaneko. In this technique, the amount of spatial carrier frequency that enabled to filter different terms in the Fourier spectrum of the recorded interferogram had to be calibrated with the use of light with a known SOP. Even in this case, the spatial carrier frequency introduced in the recorded interferogram is influenced by the relative tilt of the beam used for calibration. To eliminate the linear phase introduced by spatial carrier frequency, usually the spectrum around the carrier frequency location in the Fourier transform is shifted and brought to the centre. During this process an error of a fraction of a pixel in the shifting of the spectrum after filtering to remove the linear phase introduced by spatial carrier frequency will drastically change the measured SOP of light. For accurate SOP mapping, it is important that we eliminate the artifacts and errors due to the spatial carrier frequency in the single shot polarimeter that are otherwise very promising. In the present work, we propose a Mach-Zehnder interferometric polarimeter that uses a common path Sagnac interferometer to generate reference beams with orthogonal state of polarization. By taking advantage of the inherent stability of the proposed common path Sagnac interferometer against surrounding vibrations and air turbulences, a simple calibration scheme using a light of known state of polarization is used to map the state of polarization with better accuracy.

Electronic speckle pattern interferometry using virtual speckle patterns is a high resolution deformation measurement method. Usually, virtual speckle patterns have been produced by Hilbert transform or Carré algorithm. However, there are some problems concerning calculating time and quantity of deformation in the process of producing virtual speckle patterns. In proposed method, virtual speckle patterns are easily produced by replacing temporal information with spatial information on CCD without processing by Fourier transform or Carré algorithm. As the results, calculating cost of virtual speckle patterns is improved. It is confirmed that the new method is equal to ordinary methods in measurement accuracy.

Heterodyne interferometry is a very accurate and robust technique for measuring vibrations under industrial conditions. Typically, instruments based on this principle measure on a single point and scanning is employed to obtain operational deflection shapes. For the simultaneous measurement of vibrations (e.g. to detect transients) it is possible to use a fixed arrangement of measurement beams. Dynamic steering of multiple beams, however, is not easy to achieve. In this contribution we present a solution for multipoint vibrometry using a high resolution (HDTV) programmable spatial light modulator as the core element. By using a liquid crystal display (LCD) for displaying a dynamic hologram it is possible to independently control multiple measurement spots in three dimensions with high repeatability and accuracy. Mechanical movements that might introduce noise do not oocur. The main challenge in designing such an LCD-based multipoint vibrometer is to avoid problems due to the unwanted spurious diffraction orders that will be present when using commercially available spatial light modulators for reconstructing holograms. We present a system in which the illuminating as well as the detection is programmable. One half of the high resolution LCD is used for illumination and the other half is responsible for the detection. Different possible methods to avoid spurious diffraction orders are shortly discussed. Emphasis will be laid on a method based on complex multiplexing (using hologram optimization) and a spatial multiplexing method based on Golay arrays. We show the optical design as well as first experimental results for a single detector. Hologram computation is based on a joint optimization of the detection and the illumination hologram using a modified Gerchberg-Saxton algorithm together with combinatorial optimization of the spot/detector mapping.

A self-mixing laser interferometer has been combined with a compact and robust optical system including an adaptive optical element in the form of a voltage controllable liquid lens. The use of the liquid lens enables the self-mixing interferometer to adjust the optical focus position and the beam spot diameter on the target surface, and subsequently the feedback level within the laser cavity. The optical system has been designed to focus the beam at distances from a few centimetres from the front facet of the laser diode to infinity. With such a simple arrangement, it is possible to modify and control the intensity of the back reflected light from the target surface into the laser cavity, by simply changing the voltage applied to the lens to modify the focus condition on the target surface. The final effect obtained is full active control of the feedback level of the self-mixing effect taking place. This has allowed keeping the feedback level of the interferometer in the desired regime for measurements along very long distances and for different measurement situations, so extending the capabilities of a classical self-mixing interferometer. The advantage of the proposed adaptive optical head is thus its combination of precise metrology capabilities plus a great potential in automated feedback control and operator-free industrial applications. Signal reconstruction of the target vibration amplitude presents a maximum error of λ/16 as compared with a commercial capacitive sensor in the whole focusable range for displacement measurements. An improved working range of 6.5 cm to 280 cm staying in the same feedback regime has been experimentally demonstrated.

The authors of the paper propose a novel approach to the analysis of fringe patterns described by the Bessel function. This kind of patterns can be met while using Time Averaging Interferometry for vibration investigations. The directional spatial carrier phase shifting technique (one of the automatic fringe pattern analysis methods) is proposed to decode the information encoded in the function argument. With additional correction process (the analyzed J₀ function differs from the sinusoidal one) the investigated object vibration amplitude may be evaluated. An unquestionable merit of the proposed technique is its processing simplicity and single pattern analysis scheme. The paper presents features of the proposed approach as well as its possible measurement errors, via extensive numerical simulations. Performed experiments corroborate the theoretical findings.

In automatic analysis of the time-average digital speckle interferogram, the great challenge is to get proper intensity variation between different fringes and smoothness in the line profile of intensity distribution, so as it approaches the governing Bessel function/map. An image processing scheme based on wavelet denoising and morphological operation has been investigated which is very effective in reducing speckle index, width reduction of the bright fringes and in getting proper line profile for intensity distribution. Improvement in signal to noise ratio (i.e. decrease in speckle index) upto 28 times has been observed.

We have developed a high-sensitivity, low-coherence dynamic light scattering system for the measurement of particles a few tens of nanometers in size. A Mach-Zehnder interferometer and a confocal optical system were adopted for improved sensitivity to scattered light intensity. The developed system can detect scattered light 3000 times weaker than that detectable by a previous system. We applied the newly developed system to measure the particle size distribution of 10 vol.% polystyrene particles with an average diameter of 13 nm. The obtained particle size distribution agreed quite well with a distribution determined by transmission electron microscopy.

Current methods to characterise specific properties of polymeric nanocomposites (PNCs), such as particle loading and dispersion profile, rely on a number of techniques that require special sample preparation and treatment, are very expensive, require long measurement times and quite often produce ambiguous results that are difficult to evaluate and interpret. In addition, given their complexity, they are not entirely suited for in-situ industrial environments. This paper presents alternative techniques based on optical diffraction and diffusion mechanisms combined with signal processing that can successfully discriminate between different particle loadings and levels of dispersion. The techniques discussed in this paper are Fourier-domain optical coherence tomography in the infra-red, Fraunhofer wavefront correlation in the visible red and oscillatory photon correlation spectroscopy in the visible green parts of the spectrum. Most importantly, they are non-invasive, are compact, fast and efficient, can potentially analyse large areas of the material and therefore suited for a wide variety of research and industrial situations.

A Mueller Matrix Imaging Ellipsometer system is operated in transmission and used to study nematic textures in colloidal dispersions of synthetic Na-fluorohectorite clay platelets in solution. It is clearly observed that the anisometric particles organize into phases with strong birefringence, which results in a strong retardance. The Mueller matrix imaging technique supplies an image of the retardance matrix, even in the presence of other effects such as light scattering and diattenuation. The spatial variation of the absolute value of the retardance, the orientation of the fast axis of the retardance, the total diattenuation and the orientation of the diattenuation are presented. In particular, from knowledge of the anisotropic shape of the particles, the orientation of the particles within ordered domains, and the density of the particles within the domains are spatially determined. The experiments are based on adding synthetic clay particles into a solution contained in a thin rectangular glass container. Upon letting gravitation act on the sample, different phases appear after a few weeks. One phase contains nematic textures and we are able to determine the ordering and also estimate the density of the domains/texture within the phase, in addition to estimating the local order within a domain with an image resolution of 12 μm.

Automatic dimensional inspection of 3D articles with high resolution and productivity is an urgent problem for industry. It takes solving some measurement basic and applied tasks. Using the optical inspection methods, it is essential to take into account the influence of 3D bodies' extension on their Fraunhofer diffraction pattern and images. This influence strongly depends on the configuration of illumination, which therefore is fundamentally important. The solution for diffraction phenomena by volumetric slit under inclined plane and spherical wave illumination has been represented. The obtained results can be applied for investigation of formation and high-frequency filtering images of 3D bodies of constant thickness. Ensuring the safety and high operation reliability of nuclear reactors takes 100% inspection of geometrical parameters of fuel assemblies, which include the spacer grids performed as cellular structure with fuel elements. The required spacer grids geometry of assembly in the transverse and longitudinal cross sections is extremely important for maintaining the necessary heat regime. A universal method for 3D spacer grid inspection using the diffractive optical element, which generates as the structural illumination, a multiple-ring pattern on the inner surface of a spacer grid cell is investigated. Using some diffractive optical elements one can inspect the nomenclature of all produced grids. Experimental results for semi-industrial version of spacer grid inspection system are presented. A structured light method and testing results of pilot system for noncontact inspection of wire wear and its defects for train electro-supply network are given and discussed.

Phase shifting shearography monitors the mechanical behaviour of an object under load, which makes it a valuable tool for non-destructive testing. However, it cannot determine the depth of defects, and sometimes, the gradient of the displacement of the whole object is so large that it hides small deviations caused by flaws. Our approach to overcome these limitations is based on shearographic imaging of the gradient of the displacement field of an object that is periodically loaded by a modulated excitation. After unwrapping the stack of fringe images, the local phase and amplitude of the periodical object displacement can be retrieved by a pixelwise discrete Fourier transformation. The displacement of the test object itself is mathematically reduced since only the sine-coded object response is extracted by the Fourier transformation. Depth range can be adjusted since the thermal diffusion length of the thermal waves depends on their frequency. Since all images are used for evaluation (and not only one fringe image like in conventional speckle-interferometry), the signal-to-noise ratio is substantially increased. This paper discusses the performance of this technique on model samples and demonstrates the advantages of this approach on modern automotive and aerospace structures.

Laser ultrasonics was applied to the manufacturing control of the quality and integrity (no failure) of coated spherical particles designed for High Temperature Reactors (HTR). The coating of the nuclear fuel kernel is designed to prevent from the diffusion of fission products outside the particle during reactor operation. The quality assessment of the coating layers is of major importance. Using laser ultrasonics, we determined the vibration eigenmodes of dummy HTR particles. The vibration spectrum of a HTR particle provides a non-destructive method of evaluating some important mechanical parameters of the coating. Moreover, without damaging the particle, the laser ultrasonics technique allows to test the presence of a crack in the SiC layer, through the observation of the particle vibration spectrum, which is significantly changed, compared to that of a defect-free particle. We applied nanosecond acoustic pulses, i.e., high frequency laser-generated ultrasound, to measure the acoustic velocity of longitudinal waves the SiC layer. This technique provides an alternative method of evaluation of the Young modulus of the SiC layer. We measure the velocity of surface acoustic waves (SAW) on a pyrocarbon layer cross-section and we demonstrated that the anisotropy of the internal pyrocarbon layer can be evaluated by laser ultrasonics.

We use optimized concepts to measure directly low absorption in optical materials and thin films at various laser wavelengths by the laser induced deflection (LID) technique. An independent absolute calibration, using electrical heaters, is applied to obtain absolute absorption data without the actual knowledge of the photo-thermal material properties. Verification of the absolute calibration is obtained by measuring different silicon samples at 633 nm where all laser light, apart from the measured reflection/scattering, is absorbed. Various experimental results for bulk materials and thin films are presented including measurements of fused silica and CaF₂ at 193 nm, nonlinear crystals (LBO) for frequency conversion and AR coated fused silica for high power material processing at 1030 nm and Yb-doped silica raw materials for high power fiber lasers at 1550 nm. In particular for LBO the need of an independent calibration is demonstrated since thermal lens generation is dominated by stress-induced refractive index change which is in contrast to most of the common optical materials. The measured results are proven by numerical simulations and their influence on the measurement strategy and the obtained accuracy are shown.

TSV (Through Silicon Via) is a vertical via that passes through a silicon wafer or chip. This technology is a major enabler for three-dimensional integrated circuits (3D ICs) of stacking different functional chips. Vertical stacking chips of 3D ICs allows gates to be placed closer and thereby provides more computing process in a compact space. As TSV technique with unique processing steps that are not used in standard 2D ICs, a number of new parameters need to be measured and controlled. TSV etching depth is a critical parameter for ensuring the performance of 3D ICs, thus metrology and inspection of the TSV etching depth are very profitability of the overall manufacturing process. Spectroscopic reflectometry (SR) is currently being used in industry to measure the internal reflectance of thin films, from which the thickness and other properties can be obtained. It is a non-contact and non-destructive in-line metrology tool. In this study, we demonstrate the use of SR by employing the fast Fourier transform (FFT) algorithm for measuring the etching via depth and the thickness of oxide layer in one shot measurement. First, the specifications of reflectometer system, such as spectral range and resolution of spectrometer for depth analysis are discussed. The depth resolution is better in the longer measuring spectral range, thus small difference of TSVs' depth can be well distinguished. The spectrometer with high resolution is used to collect the authentic spectrum from etching depth with high aspect ratio. We verified our system through a mutual measurement comparison with the national standard traceable step height system. Our system is capable of measuring step height up to 100 um and measurement precision is in the range of 0.6 um. In this report, TSV arrays with nominal CD 5~25 um, and aspect ratio up to 10 are measured. Metrology results from actual 3D interconnect processing wafers indicate our system provides excellent correlation to cross-section scanning electron microscope (SEM) measurement results. The maximum discrepancy between each other is smaller than 1 um.

We report on the fabrication of optical Bragg type phase gratings in polymethyl methacrylate substrates irradiated by a femtosecond Ti: Sapphire laser. In order to investigate the distribution of the refractive index change produced by the femtosecond laser irradiation, we performed a two-dimensional visualization and spatially resolved optical analysis of the induced refractive index profile by using a digital holographic technique and an adaptive-iterative algorithm for wavefront reconstruction. The technique gives a direct and quantitative two-dimensional profile of the index of refraction in irradiated samples, providing information how the fabrication process depends on the laser irradiation.

Laser structuring is a rapidly developing manufacturing technique with long-term technological impact on future economics and ecological challenges. Due to its high process flexibility, the laser structuring system permits the structuring of different work pieces (different forms and structure complexity) with the same machine configuration. A crucial fact is the process knowledge and its control. The state of the art in laser structuring has however a crucial deficit. Present structuring systems contain no metrology setup to detect the shape geometry and contour accuracy before, during or after the structuring process. Therefore no result feedback to the machine can be accomplished and consequently a process control based on the real machined surface is not possible. In order to close this technology gap and assure an automated and robust manufacture process, a metrological system needs to be integrated to the process. In this work the concept and the development of an adjustable optical coherence tomography measuring system based on the analysis of the frequency domain (FD-OCT) with sub-micrometer accuracy for the in process measurement in a laser structuring machine is described. Goal of the research presented here is the development of the measuring system, with special focus on the spectrometer development (optical and software) and machine integration (optical and mechanical), as well as the development of an innovative wideband source based on amplified spontaneous emission (ASE) in ytterbium-doped double-clad fiber.

In-process shape measurements of rotating objects such as turning parts at a metal working lathe are of great importance for monitoring production processes or to enable zero-error production. Therefore, contactless and compact sensors with high temporal resolution as well as high precision are necessary. Furthermore, robust sensors are required which withstand the rough ambient conditions in production environment. Thus, we developed a miniaturized and robust non-incremental fiber-optic distance sensor with dimensions of only 30x40x90 mm³ which can be attached directly adjacent to the turning tool bit of a metal working lathe and allows precise in-process 3D shape measurements of turning parts. In this contribution we present the results of in-process shape measurements during the turning process at a metal working lathe using a miniaturized interferometric distance sensor. The absolute radius of the turning workpiece can be determined with micron precision. To proof the accuracy of the measurement results, comparative measurements with tactile sensors have to be performed.

Optical interferometry techniques were used for the first time to measure the surface resistivity/conductivity of carbon steel samples in blank seawater and in seawater with different concentrations of a corrosion inhibitor, without any physical contact. The measurement of the surface resistivity/conductivity of carbon steel samples was carried out in blank seawater and in seawater with a concentration range of 5-20ppm of KGR-134 corrosion inhibitor, at room temperature. In this investigation, the real-time holographic interferometry was carried out to measure the thickness of anodic dissolved layer or the total thickness, U_total, of formed oxide layer of carbon steel samples during the alternating current (AC) impedance of the samples in blank seawater and in 5-20 ppm KGR-134 inhibited seawater, respectively. In other words, the surface resistivity/conductivity of carbon steel samples was determined simultaneously by holographic interferometry, an electromagnetic method, and by the Electrochemical Impedance (E.I) spectroscopy, an electronic method. In addition, a mathematical model was derived in order to correlate between the AC impedance (resistance) and to the surface (orthogonal) displacement of the surface of the samples in solutions. In other words, a proportionality constant (surface resistivity (ρ) or surface conductivity(σ)=1/[ surface resistivity (ρ)] between the determined AC impedance (by EIS technique) and the orthogonal displacement (by the optical interferometry techniques) was obtained. Consequently the values ρ and σ of the carbon steel samples in solutions were obtained. Also, the value of ρ from other source were used for comparison sake with the calculated values of this investigation. This study revealed that the oxide film of the carbon steel sample has been removed from the surface of the sample, in the blank seawater. Therefore, the corresponding value of the resistivity to such layer remained the same as the value of the resistivity of the carbon steel sample in air, around 1x10^-5 Ohms-cm. On the contrary, the measured values of the resistivity of the carbon steel samples were 4.91x10⁷ Ohms-cm , 5.1x10⁷ Ohms-cm, and 4.2x10⁷ Ohms-cm in 5ppm,10ppm, and 20ppm KGR-134 inhibited seawater solutions, respectively. Furthermore, the determined value range of the ρ of the formed oxide layers, 1.9x107 Ohms-cm to 4.91x107 Ohms-cm, is found in a reasonable agreement with the one found in literature for the Fe Oxide-hydroxides, i.e., Goethite(α-FeOOH) and for the Lepidocrocite (γ-FeOOH), 1x10⁹ Ohms-cm. The ρ value of the Goethite(α-FeOOH) and of the Lepidocrocite (γ-FeOOH), 1x10⁹ Ohms-cm, was found slightly higher than the ρ value range of the formed oxide layer of the present study. This because the former value was determined by a DC method rather than by an electromagnetic method,i.e., holographic interferometry, with applications of EIS, i.e., AC method. As a result, erroneous measurements were recorded due to the introduction of heat to Fe oxide-hydroxides. This led to higher value of the resistivity of the Goethite(α-FeOOH) and for the Lepidocrocite (γ-FeOOH) ),1x10⁹ Ohms-cm, compared to the determined value range of the resistivity of the formed oxide layers, 4.2x10⁷ Ohms-cm to 5.1x10⁷ Ohms-cm.

Digital holographic interferometric phase shifting method is used to calculate the refractive index profile of graded index (GRIN) optical fibre and the 3D refractive index distribution across the GRIN fibre. GRIN optical fibre sample is immersed in a suitable liquid and then Mach-Zehnder-like arrangement phase shifting digital holographic system is used. The optical phase difference due to the graded index optical fibre can be extracted by digital holographic interferometric phase shifting technique. The problem of the tilted GRIN optical fibre with respect to the reference axis is solved, since the fibre must be perpendicular to the reference axis according to symmetry considerations. The optical phase difference map along the GRIN optical fibre is used to calculate the mean values of the optical phase difference across the fibre. The refractive index profile of GRIN optical fibre is calculated using the multilayer mathematical model, where the refraction of the incident rays through the fibre layers is considered. The shape parameter of the investigated optical fibre is determined. The mode field distributions can be analyzed for the used GRIN optical fibre. The calculated refractive index profile is used to reconstruct the 3D refractive index distribution across the fibre sample.

The optical- functional properties of an integrated-optical strip-waveguide in a planar polymer chip are presented in this article. The waveguide was directly written into the surface of a planar polymer chip by UV-laser irradiation. Digital holographic interferometric phase shifting method is used to calculate the refractive index profile of the waveguide. This profile contains one or two zones according to the parameters of UV-laser. The mode field distribution and the effective mode indices for each zone are obtained. The study shows that the optical-functional properties strongly depend on the UV-irradiation parameters. Several mostly independently occurring photochemical processes competing with one another are proposed to explain the formation and shape of the refractive index distribution.

The presence of a residual sphericity in a reference beam causes magnification in the reconstructed image in digital holography. We discuss a method to estimate the relative sphericities in a multi-perspective multi-camera digital hologram recording unit. The digital holograms can then be compensated with numerical quadratic phase factors so that the object appears with the same magnification in all the reconstructions.

Spatial filtering techniques are used in the analysis of interferograms and off-axis digital holograms to obtain the phase information from an optical field. The masks applied for the selection of the virtual image order in the frequency space usually have regular shapes and are located by hand. Therefore, they create artifacts that hide some details in the obtained phase, especially when holograms from objects with sharp edges are reconstructed. In this work, a novel algorithm that automatically calculates and locates the mask separating the spectral orders is presented. This new method uses a distance criterion between the maximum values in the amplitude spectrum as a clustering parameter. The values for the distance parameter are changed and the results are analyzed for a simulated image-plane hologram. As an example of the algorithm application, a digital hologram obtained from one USAF-1951 test target is reconstructed and the phase of the test target element is obtained.

Digital holographic microscopy (DHM) is an effective method that can be used to investigate transparent objects. The technique allows to get both intensity and phase distributions of wavefronts transmitted through samples without scanning or destructing them. In this paper, a DHM setup with sub-micrometer resolution is used to record the deformation of hydrogels during the swelling and shrinking process. To overcome the out-of-focus imaging caused by the shifting and deformation of the samples, numerical focusing instead of mechanical focusing is employed. The intensity images at different depths can be reconstructed by using one single hologram, and the phase change as a function of the time can be also determined.

Characterizing tracer micro particles in fluids is of a great challenge for digital holographic techniques. The real locations and the number of these particles are the main parameters in such studies. For the first parameter, holographic techniques are very useful, unfortunately, they suffer from the large depth of focus which increases the location uncertainty of the particles. To minimize this uncertainty, we proposed a two orthogonal views system which, from our point of view, makes the location more precise by crossing the two views data in the reconstruction process. For the second parameter (particle number), off-axis configuration is recognized to be more convenient for large particle numbers than the in line configuration. In order to validate the effectiveness of the off-axis configuration in terms of number of tracer particles, we carry out some experiments. The number of particle was increased continuously after each recording. We have also tried to keep unchanged the experiment conditions during all the recording process. In the present work, we describe the manner in which the experiments were conducted and the obtained results in term of diffraction efficiency of the reconstructed holograms.

In digital holography interference fringe pattern is formed on a computer-aided CCD camera target and recorded by the computer. The object wave is reconstructed electronically by using this numeric hologram. In an off-axis holography the zero order and two first orders are formed in separate positions. However the zero order decreases the quality of any of the two formed images. In this process a zero- order component appears. This component decreases quality of the reconstructed image. In this work a method is proposed with which we can eliminate this component effectively. This technique is based on recording two holograms for two angular positions of the CCD camera. The performed experiments verify the effectiveness of the procedure.

Makyoh topography is an optical tool for the flatness testing of specular surfaces, based on the defocused detection of a collimated light beam reflected from the tested surface. The reflection image is related to the relief pattern of the tested surface due to the focusing/defocusing action of the surface irregularities. The main application of the method is semiconductor technology. In this contribution, the effects of the coherence of the illumination on the Makyoh imaging is analyzed. It is shown that coherence effects are expected even for white-light illumination because of the small source size. Under optimum imaging conditions, coherence is manifested as diffraction patterns around isolated defects and at sample edges, and as speckle due to surface roughness. These phenomena are analyzed as a function of surface roughness, illumination coherency and wavelength, light source size and instrumental geometrical parameters. The findings are illustrated with experimental images of various semiconductor samples.

Thanks to its robustness and reduced sensitivity to vibrations and air turbulence, spatial phase-shift interferometry (SPSI) is a measuring technique of particular value in industrial environments. Making use of a commercial CCD camera connected with a PC we have set up an essential system that acquires and processes the fringe pattern, extracting the relevant features of the phenomenon being observed. The basic algorithms for phase recovery are available from the literature. Here we present a variant of one of such algorithms and describe in detail its implementation in our SPSI system. Experimental results are presented, showing the effectiveness of the overall measuring chain.

Development of Spatial Light Modulators (SLM) opened a new area in coherent optical metrology. These modulators are capable to optically reconstruct digital holograms; therefore they can be used as active holographic optical elements in Electronic Speckle Pattern Interferometry (ESPI) or in digital holographic interferometry. SLM is also capable to generate computer calculated wave fronts (not belonging to an existing object), and multiple projections can be performed during the measurement time. Using this feature active measuring system can be built. In our work adaptive comparative ESPI measurement is done, where an optically reconstructed image of a computer generated hologram is used for holographic illumination of another object, with which difference deformations can be calculated. These active interferometers can continuously adapt themselves to the change of measuring conditions, because the test displacement profile can be compared with a suitable arbitrary master displacement profile in a relatively simple optical setup. This approach is a straightforward digital implementation of the analogue comparative measuring technique, where regular hologram plates are used to store and reconstruct optical wavefronts.

When testing the optical surface errors with an interferometer, it is always important to determine the residual errors in the interferometer optics. The calibration of reference optic for proper accuracy is very important issue if the precise phase measurement results are to be obtained using interferometer. A simple ball calibration method is discussed and the sufficient number of measurements for the ball averaging calibration is determined. Further we analysis some errors, which limit the performance of the calibration method by using a combination of both ray optics and wave optics approach.

In this report, error estimation method of phase detection in phase shift method is proposed. Phase detection algorithm extracts phase of modulated signal from several numbers of interferogram that acquired during phase shifting. The fourier domain expression of phase detection algorithms show frequency response for sine and cosine components. And it shows behavior for phase detection in the case that phase shifting error exists. However, these two response functions, those are response function for sine component and that for cosine component, do not directly show frequency response of phase detection itself. On the contrary, newly developed frequency response function, which is derived from these two frequency response function, directly shows frequency response of phase detection. And it clearly shows the behavior of phase detection algorithm when phase tuning error exists. The newly developed frequency response function is similar to the Bode plot. The magnitude plot shows sensitivity for frequency components. And the phase plot can be used for error estimation of phase detection. There is good agreement between the developed frequency response function and calculated error value. These results of comparison between error estimation using developed frequency response function and calculated error value are shown in this report.

We apply a hybrid light source with adjustable spectrum to Scanning White Light Interferometric MEMS device characterization. The source combines light from a blue laser (409 nm), a fluorescent material (emission peak 521 nm), amber LED (597 nm) and cyan LED (505 nm) to cover the visible wavelengths. The Gaussian spectrum of the light source reduces interference ringing and improves surface localization, which is important when imaging diffuse surfaces or layered structures. The new light source allows both stroboscopic illumination and spectrum shaping during a measurement. Changing the illumination spectrum allows one to maximize the reflection from the measured surface - compared to reflections from other surfaces - as a mean to improve signal-to-noise-ratio. To validate the source we measured static MEMS samples featuring known step heights using the light source at three different mean wavelengths (508 nm, 524 nm and 579 nm). The measured step heights (7.029 ± 0.045 μm, 7.002 ± 0.041 μm and 7.005 ± 0.056 μm) were close to those measured using a halogen lamp (7.025 ± 0.020 μm). Interferograms without the side lobes typical for white LEDs were achieved. The FWHM of the interferogram of the combined light source was (1.859 ± 0.008 μm).

This paper presents a methodology for providing traceability to OCT measurements linked to Length SI unit. The link to primary length standard is provided by an interference microscope (IM). The chosen transfer standard was a step height gauge block. The results for IM and OCT showed good agreement for step height standards, such that the OCT will be able to perform reliable measurements of complex surface topographies and to ensure traceability to the length scale. The main uncertainty components were evaluated for the OCT system. In addition, OCT also was used for measuring a surface roughness standard -a depth standard - in order to test this methodology for round groove profiles. Results were found to be in good agreement with the calibration certificate.

Scanning white-light interferometry (SWLI) provides the capability of fast and high-precision three-dimensional measurement of surface topography. Nevertheless, it is well-known that white-light interferometers more than imaging microscopes suffer from chromatic aberrations caused by the influence of dispersion. Chromatic aberrations lead to systematic measuring errors in SWLI, especially on micro-structures with curved or tilted surface areas. For example, the plane glass plates used in a Mirau-interferometer are a potential source of dispersion. If this influence is not completely corrected for, errors in height measurement occur. In addition, the magnitude of these errors strongly depends on whether the coherence peak's position or the phase of an interference signal is evaluated. This study is intended to overcome these difficulties by a dispersion optimized white-light interferometer. The design corresponds to a Mirau-interferometer, but in order to reduce dispersion phenomena, a reflective Schwarzschild microscope objective is used. For beam splitting a so-called pellicle is positioned in-between the objective and the measuring object. The dominant effect, which limits the accuracy of the interferometer is supposed to depend on multiple reflections from the front and the back side of the pellicle beam splitter. As a consequence, ghost signals were measured in addition to the typical white-light interference signals. This indicates that multiple reflections influence the results and finally limit the accuracy of the interferometer.

This paper describes common efforts of Warsaw University of Technology and Polish Central Office of Measure to build a multiwavelength interferometer with extended measurement range to calibrate long gauge blocks. To achieve this goal modified automatic fringe pattern analysis method based on fringe fraction method is proposed. The setup with special chamber with active temperature control to stabilize environmental conditions has been build. To assure correctness of measure factors like temperature, pressure, humidity and concentration of CO2 are need to be constantly monitored by network of sensors. Summarizing all this efforts we are presenting gauge blocks calibration results with uncertainty analysis.

Recently the new type of light source has been introduced to the market. Organic light emitting diode (OLED) is not only interesting because of the low applying voltage, wide light emitting areas and emission efficiency. It gives the possibility to create a light source of a various shape, various color and in the near future very likely even the one that will change shape and spectrum in time in controlled way. Those opportunities have not been in our reach until now. In the paper authors try to give an answer to the question if the new light source -OLED - is suitable for interferometric purposes. Tests cover the short and long term spectrum stability, spectrum changes due to the emission area selection. In the paper the results of two OLEDs (red and white) are shown together with the result of an attempt to use them in an interferometric setup.

A simple polarimetry configuration is used for measuring the thickness of a nonabsorbing thin film on an absorbing substrate from the ratio between the spectral reflectances of p- and s-polarized components reflected from the thin-film structure. The spectral reflectance ratio measured at a fixed angle of incidence is fitted to the theoretical one to obtain the thin-film thickness provided that the optical constants of the thin-film structure are known. This procedure is used for measuring different thicknesses of a SiO₂ thin film on a Si substrate. Moreover, an approximate linear relation between the thin-film thickness and a wavelength of the maximum of the reflectance ratio for a specific angle of incidence is revealed when the substrate is weakly absorbing. The application of this method is once again demonstrated in determining the thicknesses of the SiO₂ thin films. The results of the techniques are compared with those obtained by a technique of spectral reflectometry, and a very good agreement is confirmed.

Polarization modes dispersion (PMD) is one of the major factors that impose restrictions in the speed of optical communication links and some efforts must be done in order to properly quantify this effect. In this way we develop studies on the behavior of such a phenomenon, critical when light is transmitted through long optical fibers. The focus in this paper is to discuss the different behavior of PMD over different wavelengths ranges. Results indicate that PMD value varies, depending on the spectral region covered by the optical source. Measurements were performed using the interferometric method on three different types of optical fiber with three broadband optical sources covering the infrared spectral bands O, S, C and L. The evaluation of mean PMD is also discussed in the metrology concepts.

The Polarization-Holographic Imaging Stokes Spectro-Polarimeter developed by us is proposed to use for the determination of the characteristics of the surface of objects at optical remote sensing. Only one integral polarization-holographic element is used in such a spectropolarimeter as an analyzing detail, which makes real time complete analysis of the polarization state of light (determination of all the four Stokes parameters) possible, as well as the determination of the distribution of the polarization state of light in the image of recognizable object and the dispersion of this distribution, which provides additional information while identifying an object. A theoretical model showing the connection of the Stokes parameters of light reflected from a recognizable object with the characteristics of the material of the reflecting surface of the object has been developed that allows the appropriate correlation connections to be set. Experimentally the possibility of obtaining the distribution of the values of the Stokes parameters is shown for the samples from different materials and of a different geometric form.

We present the application of a near infra red Mueller matrix imaging ellipsometer to the characterization of plasmonic polarizers. The samples are prepared by evaporation of Au onto SiO₂ ripples. The nanostructured ripple surface has been produced by ion beam sputtering at an off normal angle of incidence. Au was thereafter evaporated onto the surface at an grazing angle. As a result, thin lines of nearly connected Au nanoparticles form along the illuminated side of the ripples, resulting in a large in-plane anisotropy of the structure. Mueller matrix imaging is used to determine the lateral uniformity of the optical signal in correlation to the real space topography of the sample, and to determine to what degree the nanoparticles tend to form a connected wire, or whether there are well separated Au particles. The success of this method in order to produce polarizers, lies in controlling the process to allow well connected lines of Au particles along the ripples, with a high degree of homogeneity. Mueller Matrix images of the sample recorded at normal incidence are shown, and the information that can be extracted from such images is discussed.

We present an optical technique to measure five-degree-of-freedom error motions of a high-speed microspindle. The measurement system consists of a rod lens, a ball lens, four divided laser beams, and multiple divided photodiodes. When the spindle rotates with its concomitant rotation errors, the rod and ball lenses, which are mounted to the chuck of the spindle, are displaced, and this displacement is measured using an optical technique. In this study, the measuring system is manufactured for trial and is experimentally evaluated. The results clarify that the measuring system has a resolution of 5 nm and can be used to evaluate micro spindle rotation errors.

Dimensional measurement of hot heavy forgings is desirable to permit real-time process control, but usually is inconvenient because of the difficulty in working with very hot workpieces. This paper presents an approach based on Two-dimensional Laser Range Sensor (TLRS). Firstly, the measurement system can be obtained by assembling TLRS, an axis of rotation, and a servo motor, which rotates and scans forgings in different planes. Then, the coordinates of points of forging's surface can be obtained in coordinate system in scanning plane. Secondly, the origin of Measurement Coordinate System (MCS) at the centre of rotation of TLRS can be located. According to the transformation between Sensor Coordinate System (SCS) and MCS, coordinates of points in different SCS can be transferred into the fixed MCS. Next, the final points of forging's surface in MCS can be obtained. Hence models of hot heavy forgings can be reconstructed by using Triangulated Irregular Network and optimized by employing Delaunay rules. Finally, different parameters of forgings, such as lengths and diameters, can be measured. In order to calibrate the measurement system, a pyramid is proposed to compute the transformation matrix between SCS and MCS based on the projective geometry theory. The new method has been verified by experiments in both the laboratory and the forging workshop. The experimental results indicate that it is much more practical for the real time on-site measurement of hot heavy forgings. This research lays a desirable foundation for the further work.

Present a novel method of 3D shape measurement of optical free-from surface based on fringe projection. A virtual reference surface is proposed which can be used to improve the detection efficiency and realize the automation of measuring process. Sinusoidal fringe patterns are projected to the high reflected surface of the measured object. The deflection fringe patterns that modulated by the object surface are captured by the CCD camera. The slope information can be obtained by analyzing the relationship between the phase deflectometry and the slope of the object surface. The wave-front reconstruction method is used to reconstruct the surface. With the application of fringe projection technology the accuracy of optical free-form surfaces measurement could reach the level of tens of micrometer or even micrometer.

Optical methods are now often used in the measuring technology. These methods have the great advantage that the inspected objects are measured contactlessly with a high repetition rate. The obtained data can be evaluated in almost real-time or in post-processing. This allows the reckoning of deformations in real-time, as well as the three-dimensional representation and the documentation of the whole process of deformation.

This paper reports on the calibration routine developed for an absolute measurement of the mean radius and the ovality of a ring. By means of six laser triangulation sensors, the measurements are performed in-process in a furnace during heat treatment. The lack of precise information about the exact position and direction of the sensors and the minimal accessibility of the ring in the furnace is challenging and leads to a complex calibration routine. The calibration includes the application of gauge rings with different diameters. The developed routine is described and calibrated measurement results are compared with coordinate measurement machine (cmm) data. Concerning the ring radius (~ 72.5 mm), the comparison exhibits a deviation to the cmm data of less than 35 μm.

This paper proposes a new type of color coded light structures for the inspection of complex moving objects. The novelty of the methods relies on the generation of free-form color patterns permitting the projection of color structures adapted to the geometry of the surfaces to be characterized. The point correspondence determination algorithm consists of a stepwise procedure involving simple and computationally fast methods. The algorithm is therefore robust against varying recording conditions typically arising in real-time quality control environments and can be further integrated for industrial inspection purposes. The proposed approach is validated and compared on the basis of different experimentations concerning the 3D surface reconstruction by projecting adapted spatial color coded patterns. It is demonstrated that in case of certain inspection requirements, the method permits to code more reference points that similar color coded matrix methods.

Laser triangulation method is not applicable in all possible areas, due to the presence of numerous disturbances. The method of predictive segmentation of laser line resistant to interference, which allows use in industrial quality control of the glossy elements, has been proposed. It requires precise synchronization with the CAD model of the scanned item. Very high accuracy of positioning is required to enable predictive segmentation of laser prole. -The worse positioning, the widest condential intervals, and worse algorithm's ability to reject specular re ections. The most universal way to synchronize the model of a part under laser scanning, with its virtual model, is to use an extra camera and some 3D matching software. This solution, however, is rather of poor accuracy -even if a high quality optics is used. Kalman ltering is used to reduce the deviation of results. To avoid problems in description of such complicated system, a coherent and homogeneous mathematical description has been proposed. It uses so-called Denavit-Hartenberg notation, widely used in robotics. Several tests has been carried out to verify the 3D matching algorithm for object-model synchronization during laser scanning. The results show clearly that the accuracy of matching can be improved by using Kalman ltering -even up to 10 times. Thanks to it, its accuracy increases to face the requirements of predictive segmentation algorithm.

Wavelet analysis is a processing method for the description of single- or multi-dimensional signals in multiple scales and therefore well suited for describing technical surfaces with variable resolution. Here optically measured height data of technical surfaces are wavelet-transformed along two dimensions with two different objectives: One is the representation with only a few coefficients in the sense of an efficient data compression, the other is the reliable detection of defects, which can be regarded as a pattern recognition task. A systematic comparison of various wavelet families results in the choice of the biorthogonal pseudo-coiflets for representing the surfaces, and differentiating wavelets like Burt-Adelson-wavelet or short-range Daubechies-wavelets for solving the defect detection problem. It is shown that the representation can be improved by not using the most significant wavelet-values - which can be interpreted as low-pass filtered coefficients, but to maintain those with the largest weights. Thus the variance between the original surface and that reconstructed from the representation data is minimized by a factor up to 4. Defect detection is best performed with separate transformation in two orthogonal directions with subsequent superposition. The procedures obtained here are applied to surfaces like a coin-surface, a copper-mirror surface, and a lacquered surface.

Lateral and axial resolution and effective depth scanning range in white Light Confocal Microscope are related to the range of longitudinal chromatic aberration of system. In this article simulation and fabrication of white Light Confocal Microscope with tunable longitudinal chromatic aberration is discussed. The simulation has been done by Zemax optical design software. Generation of longitudinal chromatic aberration has been achieved by using two biconvex lenses with focal length of 30 mm and 40 mm and a 40x microscope objective. The effect of variation of distance between lenses on longitudinal chromatic aberration was studied. In addition the optical properties of microscope such as axial and lateral resolution, numerical aperture, effective depth scanning range and total shift of chromatic aberration in optical axis direction were studied. Using this setup with a broadband source of 480nm to 650nm tunable effective depth scanning range covering 23μm to 68μm was achieved. As a result tunable axial resolution of 48nm to 159nm was obtained. Regarding the scale of the sample we could use the optimum resolution.

Linear sensor microscopy as a mode of slit microscopy is faster than confocal microscopy as it eliminates one lateral scanning but its lateral/axial resolution are lower. Regardless specific image formation characteristics dependent on illumination mode its circular symmetry is lost therefore lateral resolution anisotropy arises. The purpose of this work is to evaluate the application of a low-cost scanning-stage bench-microscope in brightfield reflection mode using a linear sensor for shape and thickness measurements. Firstly we describe overall system architecture emphasizing its effectiveness to easily accommodate different optical setups. In particular different configurations of scanning microscopes are briefly described and a comparison of its image formation characteristics is presented giving special attention to the effect of slit illumination/detection. Results of lateral resolution in both lateral orientations show slit illumination should be used. A reconstruction method used to build three-dimensional representations from images of 3D structures results in relief borders shapes equally defined independently of its orientation relative to sensor. Further results of its application for the measurement of height and thickness of PCB tracks show its inherent ability though a more robust reconstruction algorithm integrating data from light distribution in sensor is being developed to improve clearness and measurement accuracy.

Grinding processes causes the formation of a characteristic surface structure, known as chatter marks. In this work, an angle-resolved light scattering technique is used to characterise them. In order to identify the chatter marks in a measured profile, the fast Fourier transform (FFT) is usually applied to the measured data. The FFT, however only for strictly periodic data yields unambiguous results. To overcome this, the multiresolution analysis (MRA) is also applied by means of the lifting scheme. In this manner, it is shown that chatter marks, for example, can be uniquely identified by applying the multiresolution analysis to the angle-resolved light scattering data, even when FFT fails to do this. Thus MRA alone or alternatively in combination with FFT, opens new opportunities for optical online control in case of industrial surface finishing processes.

Fogging is commonly observed when humid-warm air contacts the cold surface of a transparent substrate, i.e. eyewear lenses, making the observed image blurred and hazy. To protect from fogging, the lens inner surfaces are protected with Anti-Fog coatings, which render them hydrophilic and induce water vapor condensation as a smooth, thin and invisible film, which uniformly flows down on the lens as the condensation progresses. Coatings differ in protection level, aging kinetics, and susceptibility to contamination. Some perform acceptably in limited conditions, beyond which the condensing water film becomes unstable, nonuniform, and scatters light or shows refractory distortions, both affecting the observed image. Quantifying the performance of Anti-Fog coated lenses is difficult: they may not show classical fogging and the existing testing methods, based on fog detection, are therefore inapplicable. The presented method for evaluating and quantifying AF properties is based on characterizing light scattering on lenses exposed to controlled humidity and temperature. Changes in intensity of laser light scattered at low angles (1, 2 4 and 8 degrees), observed during condensation of water on lenses, provide information on the swelling of Anti-Fog coatings, formation of uniform water film, going from an unstable to a steady state, and on the coalescence of discontinuous films. Real time observations/measurements allow for better understanding of factors controlling fogging and fog preventing phenomena. The method is especially useful in the development of new coatings for military-, sport-, and industrial protective eyewear as well as for medical and automotive applications. It allows for differentiating between coatings showing acceptable, good, and excellent performance.

Dynamic concentricity measurement of small holes distributed in large room is valuable in assembling some big and complex optical facility. It's not feasible for the conventional measurement with portable CMM or laser tracker. A solution of dynamic concentricity measurement is put forward in this article, in which low power laser was selected as reference and camera &lens were used to acquire images of holes and laser spots. The relative orientation of hole and spot could be detected after image processing. To overcome the shortcoming that the edge of laser spot could not be detected for laser's Gaussian character with traditional method, a virtual annular quadrant (VAQ) method was proposed to determine the relative orientation between small holes and laser spot. With the simulation of VAQ method, the property was analyzed and the parameters of VAQ were optimized with the simulation results. Experiments were carried out to test VAQ method, and comparison of simulated and experimental results has confirmed the accuracy of VAQ method. A dynamical concentricity measuring system based on VAQ method is developed, which can perform one measurement in 5 seconds and has accuracy of about 0.015mm.

The proper alignment of the individual elements in an optical system is a crucial point in the final performance of an optical system. The developed method we present is aimed to detect and quantify misalignments of decentering and tilt in imaging optical systems with a non-expensive system. This method is based in the comparison of different image parameters values. These parameters values are obtained through the analysis of the image formed by the optical system under study of an object composed of an array of point sources. The method has been validated by obtaining the behavior curves of the parameters for a gauss system in front of decentering up to 0.3mm and tilt up to 1°.

We describe a visual method for aligning physically separated, large structures using a Bessel beam to define a common datum. The equipment consists of an alignment telescope, used to generate and project the optical beam, and a series of crosswire targets fitted to each structure. Alignment is achieved by eye using a loupe or CCD camera to observe superposition of the Bessel intensity structure and crosswire shadow. The method is simple and intuitive, and can be implemented on a low budget. The combination of structured beam profile and low beam divergence allows a best-case alignment accuracy of 10 microns under lab conditions for beam lengths of 19 metres, decreasing to 30-50 microns r.m.s. for field measurements. The self-regeneration property of the Bessel beam facilitates the location of multiple beam targets with negligible degradation in beam quality. Error sources include Bessel ring - target wire mismatch, target centering/ roundness errors, and air turbulence.

The research is based on a shift control system built on autoreflection scheme. The aim is to examine the possibility of using of the cat's eye reflector for the autocollimating alignment telescopes instead of more common tetrahedral reflectors (e.g. corner cube prism). Zemax simulations were made to study the influence of beam and image deformation (caused by this reflector) on the total system error. It is concluded that systems with large linear measurement range should have more exacting requirements of the mirror linear position adjustment while ones with small range require an accurate mirror tilt control. The alignment requirements for the cat's eye reflector were also estimated.

The expansion of the world economy has enabled easy access to suppliers of optical components and systems throughout the world. Unfortunately, all manufacturers do not adhere to the same quality standards, so the need for accurate and cost effective inspection has never been greater. To address this growing demand, an economical platform for evaluating the performance of visible, NIR, and LWIR lens assemblies has been developed and will be presented.

The Ronchi test with a Liquid Crystal Display (LCD) phase grating is used for testing convergent optical systems. The rulings are computer-generated and displayed on the LCD. We prove that it is possible to make a variable electronically phase grating by using an LCD. By displaying various phase-shifted rulings and capturing the corresponding ronchigrams, the phase is obtained with the conventional phase-shifting algorithms. Experimental results are shown.

SCOTS (software configurable optical test system) is a useful tool that can provide lens manufacturers with the ability to evaluate the net performance of a lens system without the use of complex metrology systems and setups. This technique is based on measuring the transverse ray aberrations of rays to obtain wavefront information using transmission deflectometry, the refractive equivalent of reflection deflectometry. Some work using deflectometry on refractive surfaces has been briefly reported in the past, where the power of a single lens has been the measurement objective. Results showing the use of deflectometry on reflective optical surfaces, such as the primary mirror of the Giant Magellan Telescope (GMT) show that this method has a large dynamic range in which measurement accuracy is comparable with those of interferometric methods; generating interest on our part, to investigate deflectometry for refractive systems in more detail. In this paper, we focus on reporting initial tests using SCOTS by measuring simple refractive elements, such as 1" diameter biconvex BK7 lenses. Results indicate a good agreement when comparing them with equivalent MATLAB/ZEMAX wavefront measuring models, which include the measured lens parameters, where the estimated and measured wavefront RMS values and spherical aberration Zernike coefficient agree on average to within 10nm. We also investigate the effect of the chromatic aberration on the refractive optical system by collecting data using three different wavelengths: 620nm, 550nm and 450nm. The alignment of the test setup was done rapidly and we used an LCD screen with a pixel pitch of 0.1905mm. The camera used for the measurements was a simple digital CCD camera.

We report fabrication of a high pressure optical fiber sensor by using a fat long period fiber grating (FLPFG) for downhole applications. The pressure sensitivity of the bare optical fiber is low so we have designed a mechanical transducer for increasing the pressure sensitivity and possibility of installation the sensor in downhole. The pressure along the longitudinal direction changes the physical characteristic of the FLPFG and result in shifting the resonance wavelength. The FLPFG sensor has been installed on transducer and the pressure sensitivity of the fiber sensor has been measured. Since the temperature changes can affect the FLPFG output, the high pressure vessel was isolated and the temperature was kept constant during the experiment. Pressure sensitivity of the FLPFG sensors has been measured by increasing the pressure from 1500 psi to 10000 psi in steps of 700 psi which is equal to -1.04 pm/psi. With a 10 pm resolution for the wavelength shift detection our OSA, detection limit of our device at room temperature for pressure measurement is calculated to be 10 psi.

This paper describes a motion-visualization technique for a sample with rough surface by using a stroboscopic oblique-incidence interferometer. To observe a vibrated rough surface, we focused on an oblique-incidence interferometer. The oblique-incidence interferometer is well suited to analysis the rough surface and a displacement of several micrometers because a scattering at a rough surface is reduced. However, by using a continuous light, a visibility of the fringe pattern at a vibrated surface in the ultrasonic region is not good. Therefore, the oblique-incidence interferometer is not suitable for analysis of the ultrasonic vibration. To overcome the problem, a pulsed light synchronized with a vibrated sample was used as a light source by an acousto-optic modulator. To control timing between a reference signal and an input signal of the light source by using a common oscillator, time-resolved behavior of the stator can be measured. By using the interferometer, we have succeeded to detect a periodically movement of a fringe pattern of the vibrated of the stator.

This paper presents the optimized optical fiber sensor as a device allowing real-time monitoring of rotation of industrial machines parts such as shafts, impellers, compressors, mixers, etc. With proper configuration it is possible to continuously monitor the rotation frequency and phase, and thus synchronize the work of separate parts of machinery. The main principle or work is similar to standard open-head reflective sensors, but in this case head is shielded by special protective glass and immersive layer. In the paper, response curves for the different head models were shown. Also, the results of measuring and comparing the shape of the rotor blades were shown. Authors demonstrated sensor ability to measure the frequency and amplitude of the additional vibration of the rotor. For comparison, we also demonstrated a low amplitude micro-vibration measurement with a piezoelectric plate as other test object.

Condition monitoring of electromechanical equipment for heavy industry places special requirements on the environmental sensors' construction. Widely available electronic devices can easily suffer from the electromagnetic interference or may pose fire hazard. An important category of dedicated sensing devices emerged during the expansion of fiber optic technology in the last few decades. In this paper, contributing in the basic research in the field, a novel kind of intrinsic intensity fiber optic vibration sensor is proposed. We present a fiber loop based opto-mechanical transducer utilized in two configurations: the inertial sensor system working as accelerometer and a distributed vibration sensor. The complete mathematical model for the latter type configuration has been introduced, as well as some results of preliminary experimental tests on both sensor concepts have been presented.

Within an ESA funded project combustion chambers of Ariane V rockets are investigated for further development. Due to temperature gradients of approximately 1300 K/mm in the combustion chamber during launch, material damages occur because of the Doghouse effect. To avoid these damages, the combustion chambers have to be redesigned wherefore the occurring temperatures have to be measured with an uncertainty of ±5 K. In order to measure the temperature in the small layer between the hot exhaust emissions and the coolant, optical fiber sensing is deployed. Embedding special optical sensor fibers that are high temperature resistant within the material allows measuring the wall temperature directly. In order to demonstrate fiber optic sensing for high temperature and strain measurement, Thermo Mechanical Fatigue (TMF) panels, constructed as sandwich structure have been developed that represent the combustion chamber walls. Coated fibers which are installed in the the panel can be subjected to thermal loads up to 1000 K inside a high temperature oven. Online measurements of FBG sensors inscribed in the embedded optical fibers can be carried out. The measurement results of the FBG sensors exactly match the data of the electrical reference sensor. For FBG readout we use our newly developed Scanning Laser (SL) Interrogation System which uses a tuneable laser source. The output wavelength is determined by a set of control currents. In order to archive the required accuracy a Current Control Unit (CCU) stabilizes the control currents and thereby the output wavelengths. The CCU significantly improves the accuracy and additionally enhances the measurement rate. The high temperature measurement results demonstrate compatibility with the requirements.

Optical vibration measurement systems are excellent tools for characterizing ultrasonic transducers. This paper presents measurements on immersed arrays of capacitive ultrasonic transducers (CMUTs) using a heterodyne interferometer. The interferometer allows measurements of vibrations from DC up to 1 GHz with a noise floor of ~1pm/√Hz. Previously CMUTs have been characterized in air. The transducer is intended for intravascular use. Therefore the CMUTs were characterized in the transparent fluids kerosene and rapeseed oil that have acoustic properties closer to blood. The optical measurements on immersed CMUTs were validated by assessing the measurement errors caused by the acousto optic effects in the fluid. When immersed there is significant cross coupling between individual CMUTs within an array. Simulations presented here indicate that this causes an acoustic wave mode that is bound to the interface between the CMUTs and the fluid. This is confirmed by measurements of the phase velocity and attenuation coefficient of this wave. The measurement results indicate that the wave exists up to a maximum frequency and that the attenuation constant increases with increasing frequency. Rapeseed oil causes a significantly larger attenuation coefficient than kerosene, which most probably is due to a considerable difference in fluid viscosities. There was a mismatch between the simulated and measured phase velocity for low frequencies. It is likely that the cause of this is coupling between the fluid CMUT interface waves and Lamb waves in the substrate of the CMUT array. Measurements performed with the heterodyne interferometer have confirmed the presence of dispersive waves bound to the surface of the transducer by directly showing their propagation along the array. The setup has also characterized the bound waves by measuring dispersion relations.

When two similar gratings are superimposed, the transmission function of them varies with the displacement of one grating with respect to the other. The transmitted light intensity versus displacement is proportional to the autocorrelation of the transmission function of the gratings. In this paper, it is shown by measuring the latter function for gratings of pitches in order of a fraction of millimeter, submicron displacements can be measured. More precision is easily available by increasing the area of gratings and the detector gain. The presented technique is not expensive, complicated and sensitive to environmental vibrations.

The data from a monitored structure/object should be easy acquired, processed and sent to the user, who can assess the health of a structure in short time and schedule necessary maintenance in order to prevent accidences. Systems which provide such information are fundamental for Structural Health Monitoring (SHM). In the paper novel optical sensor designed for in-plane displacement and strain monitoring in crucial points of a big engineering and civil structures is presented. It combines two techniques: Grating Interferometry (GI) and Digital Speckle Pattern Interferometry (DSPI). GI requires specimen grating attached to the surface of an object under test. It is the unique technique which may provide the information about fatigue process and increased residual stresses. DSPI works with a rough object surface but due to differential measurements cannot be simply used for long time monitoring but to explore the actual behavior of a structure. The sensor which combines these techniques provides user with wide possibilities concerning functionality, measuring range, object surface and environmental conditions. The crucial issue in implementation of this sensor is the choice of its location(s) at the investigated structure. Therefore it is proposed to be as one of the elements of hierarchical sensors net, which gives complete information about structure state. As the method for supporting the choice of GI/DSPI sensor location we proposed the system based on 3D digital correlation method. The paper presents mechanical and optical sensor design along with laboratory tests of main component such as sensor heads in form of monolithic (plastic) and cavity waveguides. Finally the possible application of proposed sensor in combination with 3D DIC system is presented.

In construction of highly mechanically stable measuring devices like AFM microscopes or nano-comparators the use of low expansion materials is very necessary. We can find Zerodur ceramics or ULE glasses used as a frame or basement of these devices. The expansion coefficient of such low-expansion materials is lower than 0.01 x 10^-6 m•K^-1. For example in case of a frame or basement 20 cm long it leads to a dilatation approximately 4 nm per 1 K. For calculation of the total uncertainty of the mentioned measuring devices the knowledge of the thermal expansion coefficient of the frame or basement is necessary. In this work we present a method, where small distance changes are transformed into rf-frequency signal. The frequency of this signal is detected by a counter which measures the value of the frequency with respect to an ultra-stable time-base. This method uses a Fabry-Perot cavity as a distance measuring tool. The spacer of the optical resonator is made from the investigated low-expansion material. It is placed into a vacuum chamber where the inside temperature is controlled. A selected mode of the femtosecond frequency of the femtosecond comb which represent the distance changes of the optical resonator. The frequency is measured by the rf-counter which is synchronized by a time-base signal from an atomic clock. The first results show the resolution of the method in the 0.1 nm order. Therefore the method has a potential in characterisation of materials in the nanoworld.

The construction of the large size radiotelescope for the millimetre wave range requires measuring the line deformation of mirror's surface and the angle deviations of the mirror axles. Following issues dealing with this problem are described in this article: 1) the design of the angle deformation measurement system on the base of the autocollimation method; 2) the autoreflection scheme as the new type of the optic-electronic autocollimator; 3) the design of the line deformation measurement system on the base of the triangular method. The great attention during the research was paid to the experimental approval of the theoretical results. The parameters of the experimental setups are: infrared emission diode AL107B by power 15 mWt as sources of radiation; the objective by the focal length 500 mm as aperture of receiver video-camera, the CMOS matrix receiver by type OV05620 Color CMOS QSXGA with 2592*1944 pixels and one pixel size (2.2*2.2) μm² produced by OmniVision as image analyzer. The experimental error of the angle measuring system is 1.6 arc. seconds at the angular region 16 arc. minutes for 22 m distance. The experimental error of the line measurement is 0.15 mm at the range 30 mm on a working distance 18 m. This result allows the practice measuring of the construction deformations for the new large rotateable radio telescope RT-70 Suffa.

A simple technique to generate an optical frequency comb, based on a conventional dual-drive Mach-Zehnder intensity modulator, has been used as optical source for a high accuracy distance measurement in an interferometric set-up. The modulator has been driven by a direct-digital synthesizer that is able to deliver a pure ramp in frequency between 13 GHz and 14 GHz. We have obtained about 15 modes, corresponding to a spectral span of 200 GHz. This optical signal, launched in a Michelson interferometric set-up, allowed performing absolute distance measurement by sweeping the radio-frequency of the direct digital synthesizer. Measurements have been compared to a standard, which was a mode-locked femtosecond laser along with a counting interferometer. Absolute distance measurements over a range of 1 to 24 meters gave an accuracy of about ± 10 microns, with a repeatability of ± 5 microns, corresponding to a sub-ppm absolute distance measurement.

Rotary and linear position sensors are used in numerous manufacturing and automotive applications, where cost effectiveness and the ability of integration are major goals. To meet the increasing demand for competitive optical rotary encoders, in recent years a novel type of optical encoders have been proposed and demonstrated using a micro grating based encoding scheme. This proceeding will give details on the operation principle of this novel kind of position encoder and will show its performance on two exemplary implementations: A compact absolute rotary encoder with a micro-structured plastic disc, which can be manufactured in a conventional and cost effective DVD-molding process and a linear encoder which is based on a pseudo-random coding scheme. The implementation as well as results from their experimental characterization are presented.

The contribution is oriented towards measuring in the nanoscale through local probe microscopy techniques, primarily the AFM microscopy. The need to make the AFM microscope a nanometrology tool not only the positioning of the tip has to be based on precise measurements but the traceability of the measuring technique has to be ensured up to the primary standard. This leads to the engagement of laser interferometric measuring methods. We present a improved design of the six-axes dimensional interferometric measurement tool for local probe microscopy stage nanopositioning with the compensation system of angle errors. The setup is powered with the help of a single-frequency frequency-doubled Nd:YAG laser which is stabilized by thermal frequency control locked to a Doppler-broadened absorption line in iodine. The laser stabilization technique is described together with comparison of frequency stability and angle errors compensation system performance.

A novel calibration technique of 3D coordinate measuring machines using noncontact interferometric technique is described and a design of a new construction of length standards (ball bar, ball plate) for calibration of 3D coordinate measuring machines is proposed. The proposed optical technique uses as a sensor a small spherointerferometer for the determination of the coordinates of the center of the ball bar. Formulas are derived, which make possible to calculate an accuracy of the centre position of the spherical surface that is used for the length standard. An analysis of the proposed method is performed based on the third order aberration theory. The proposed technique can be used as a practical tool for a simple, rapid check of a positioning performance of 3D measuring machines.

A LED based white light source (WLS) is designed and constructed to determine the color characteristics of the samples having specular and diffuse reflectance properties at the standard measurement conditions of 0/45 and d/8. The light source is composed of high power cool white and ultraviolet light emitting diodes (LEDs) which are operable in adjustable current levels. In order to combine the light beams emerging from two LED sources, a 1x2 fiber optic combiner is used. Optical characterizations of the light source designed and influences of several colorful LEDs called Royal-Blue, Blue, Cyan, Green, Amber, Red-Orange and Red on spectrophotometric properties of the light source are investigated.

The experimental investigation of thermodynamic properties such heat and mass transfer of plasmas has many applications in different industries. Laboratory atmospheric arc plasma is studied in this work. The refractive index of the air around the plasma is changed because of convection phenomena. When the convection creates the air flowing around the plasma, the density and consequently, the refractive index of air are distributed symmetrically. Moiré deflectometry is a technique of wave front analysis which in both Talbot effect and moiré technique is applied for measuring phase objects. Deflection of light beam passing through the inhomogeneous medium is utilized to obtain the refractive index distribution. In experimental set-up, an expanded collimated He-Ne laser propagate through the arc plasma and the around air. The temperature distribution is obtained by use of thermo-optic coefficient of air. To calculate the thermo- optic coefficient and the refractive index of air for a given wavelength of light and given atmospheric conditions (air temperature, pressure, and humidity), the Edlén equation is used. The convective heat transfer coefficient is obtained by calculating the temperature gradient on the plasma border. This method is not expensive, complicated and sensitive to environmental vibrations.

As an alternative to completely destructive and mostly very time consuming methods non-intrusive and non-destructive Fourier Transform Infrared Spectroscopy has been chosen to enable an inline characterization chain for DRAM manufacturing. This characterization chain comprises the mold oxide etch profile and the step coverage control of high-k deposition. In our case Zirconium Aluminum Oxide deposited by Atomic Layer Deposition was used as high-k dielectric. The characterization of the different process steps was carried out by either absorption parameters based on molecule vibrations or optical path differences calculated from oscillations in the infrared spectra. For the last issue of successfully characterizing the step coverage of high-k deposition, a combination of two independent optical measurements was established. Therefore a volume related FTIR measurement in a DRAM array and an ellipsometric thickness determination of a 2-dimensional layer in a support area were combined. This method showed both, the deposition parameter dependence, like pulse time, precursor flow and deposition temperature as well as tool geometry dependence on the step coverage behavior. By the use of 300 mm mapping techniques a full characterization including spatial maps over the whole 300 mm wafers was possible.

This paper deals with a 3-D scanning system based on relatively inexpensive, off-the-shelf products. Although there exist many techniques for obtaining information about object position, size and form, it is still possible to find specific applications where none of the conventional methods seem to satisfy the requirements. Such applications are encountered in challenging environments where one has to simultaneously gather information quickly, with high accuracy and without interaction with the object of interest. The instruments also need to be kept simple, cost effective and robust. In this paper, we propose and investigate a system that angles a beam from a laser rangefinder along the object of interest, in order to determine the object's geometrical properties. The beam is angled by means of a galvanometer scan head. The scanned pattern is conditioned by the assumed object form and position. The pattern is adjusted during the measurement in an appropriate way so that the scanning time is minimized. The object form assumed is a series of concentric pipes of relatively small and varying diameter (10 - 50 cm). The system is designed to determine the position of the joints and the diameters of the pipe sections. The object can be at temperatures ranging from subzero to over 1300 °C. This article specifies the characteristics of the system and discusses the various parameters limiting the system performance. Although the system components were not optimal with respect to the measurement requirements, the system's performance is designated as satisfactory. The system can easily be improved by exchanging the components with more suitable units.

Constant and traceable high fabric quality is of high importance both for technical and for high-quality conventional fabrics. Usually, quality inspection is carried out by trained personal, whose detection rate and maximum period of concentration are limited. Low resolution automated fabric inspection machines using texture analysis were developed. Since 2003, systems for the in-process inspection on weaving machines ("onloom") are commercially available. With these defects can be detected, but not measured quantitative precisely. Most systems are also prone to inevitable machine vibrations. Feedback loops for fault prevention are not established. Technology has evolved since 2003: Camera and computer prices dropped, resolutions were enhanced, recording speeds increased. These are the preconditions for real-time processing of high-resolution images. So far, these new technological achievements are not used in textile fabric production. For efficient use, a measurement system must be integrated into the weaving process; new algorithms for defect detection and measurement must be developed. The goal of the joint project is the development of a modern machine vision system for nondestructive onloom fabric inspection. The system consists of a vibration-resistant machine integration, a high-resolution machine vision system, and new, reliable, and robust algorithms with quality database for defect documentation. The system is meant to detect, measure, and classify at least 80 % of economically relevant defects. Concepts for feedback loops into the weaving process will be pointed out.

The relative spectral radiant flux error caused by phosphor fluorescence during integrating sphere measurements is investigated both theoretically and experimentally. Integrating sphere and goniophotometer measurements are compared and used for model validation, while a case study provides additional clarification. Criteria for reducing fluorescence errors to a degree of negligibility as well as a fluorescence error correction method based on simple matrix algebra are presented. Only remote phosphor type LED light sources are studied because of their large phosphor surfaces and high application potential in general lighting.

An optimized algorithm of quantitative gas analysis for spectrometers based on acousto-optical tunable filters (AOTFs) is presented. Efficiency of the algorithm is based on unique feature of AOTFs - random spectral access. This property makes it possible utilization of specialized procedures for on-line processing of spectral information without any significant loss of time. The procedure of finding optimal set of spectral points has developed and presented. The optimized algorithm has been tested with use of gas analytical system GAOS comprising movable spectrometer based on double-stage collinear AOTF. GAOS uses differential optical absorption spectroscopy (DOAS) for measuring gases abundance. Optimized algorithm improves the accuracy of the results and reduces measurement time compared to spectral-scanning algorithm. It can be used for such applications as rapid analysis of emissions in emergency, the analysis of large collection of samples in the laboratory or in the production processes, etc. An optimized calibration procedure for gas analyzers employing AOTF-based spectrometers is presented. It takes into account the possible interference of the calibration coefficients of different substances and is insensitive to possible ill-conditioned calibration matrix. Using the optimized calibration procedure allows to reduce the systematic error.

In general losses of optical of less than 1 % cannot be measured precisely with the best-established techniques (e.q. two-beam spectroscopy). However, it is possible to measure losses in the 0.0001 - 0.5 % range with high accuracy using cavity enhanced spectroscopy (CES) methods. Such low losses can be measured with CES, due to an increased interaction path way with the object. The Cavity Ring-Down (CRD) technique takes advantage of the CES method and transforms the optical loss information into the time domain. Two types of CRD setups for spectrally resolved loss measurement of laser mirrors will be presented. The first setup uses a tunable laser system for serial detection of the reflectivity spectra. The second method determines the spectral losses using a super continuum source. Here, simultaneous excitation and a spectrometer based camera system for separate detection of several wavelengths is used. Results will be shown and compared with direct absorption measurements of the same sample.

Recently, the inkjet printing (IJP) technology was advised as a direct method for the fabrication of high-quality and high-precision microlenses overcoming the drawbacks of the traditional techniques which usually require multiple complex processing steps making the fabrication costly. IJP has the great advantage to be extremely versatile in definition of the patterns of microstructures to be realized employing polymers with suitable optical transmission and thermo-mechanical properties. In the present work, we reported the manufacturing of microlenses by inkjet printing Poly(methyl methacrylate) (PMMA) solutions prepared with different solvents (toluene, N-Methyl-2-pyrrolidone, chlorobenzene, ortho-dichlorobenzene) and solvent mixtures at different mixing ratios and investigated the effects of these parameters on the shape and the geometry of the microstructures. These structures were analyzed by means of interferometric Mach- Zehnder technique in confocal configuration and the wave aberrations were evaluated. The results showed the feasibility of manufacturing microlenses via IJP with diameters ranging from 40 to 90 μm and focal lengths of the order of magnitude of hundred micron.

Direct real-time measurements of the penetration depth during laser micromachining has been demonstrated by developing a novel ablation sensor based on laser diode feedback interferometry. Percussion drilling experiments have been performed by focusing a 120-ps pulsed fiber laser onto metallic targets with different thermal conductivity. In-situ monitoring of the material removal rate was achieved by coaxially aligning the beam probe with the ablating laser. The displacement of the ablation front was revealed with sub-micrometric resolution by analyzing the sawtooth-like induced modulation of the interferometric signal out of the detector system.