This PDF file contains the front matter associated with SPIE Proceedings Volume 9132 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

We demonstrate an optical profilometer composed of an ultra-stabilized mode-locked femtosecond laser, a single pixel camera, and an optoelectronic interferometer. The combination of an optical frequency comb generated by the femtosecond laser and the optoelectronic interference in radio frequecny range enables us to measure an object with a large depth much more than a wavelength of light with a wide dynamic range giving no 2π phase ambiguity. The wide dynamic range is achieved by high stability of the optical frequency comb and easy selection of the frequency. The single pixel camera is used for twodimensional imaging without a mechanical scanning. It is performed by spatial light modulation of an object beam, the coherent summation of the spatially-modulated object beam with a single photo detector, and an inverse matrix calculation. We selected two approaches to reduce the number of measurements. One was the compressive sensing that well reduced the number when an object is sparse. The other was the reversal signal generation method that reduced the number to one-half of the sampling points for any object. We demonstrated the surface profilometry for an object with the depth of several centimeters.

In the field of areal surface roughness measurement, characterization using several techniques can be helpful to better understand the performance of each technique and to improve the overall precision. Measuring exactly the same area with different techniques in practice is not easy. Such studies are of great interest in order to characterize and to understand important new materials today such as semiconductor alloys and graphene for silicon technologies, or biomaterials such as hydroxyapatite for use in human implants. In this work, two types of samples based on a silicon wafer were made by marking with a fractal, multi-scale photolithographic mask and etching. The first sample consisted of a bare silicon wafer with a pattern consisting of 2.4 μm deep numbered square features. The second sample was a rough layer of hydroxyapatite deposited from a solution of simulated body fluid on a similarly etched silicon wafer. The same zone of several squares on the two samples were measured by interference microscopy, AFM and ESEM. The 2D cross sectional profiles and 3D views from the different results were then compared using different analytical measurement software tools. While the general shapes of the measured microstructures were similar, several differences also appeared. Variations were found of up to 7 % in the depths of the etched features measured with the different techniques. This is ascribed to instrumentation calibration errors, probe/surface interactions and to differences in measurement procedures between the software used. Artifacts were also visible at square edges due to probe/source interactions.

In this paper, the establishment of a remote laboratory for phase-aided 3D microscopic imaging and metrology is presented. Proposed remote laboratory consists of three major components, including the network-based infrastructure for remote control and data management, the identity verification scheme for user authentication and management, and the local experimental system for phase-aided 3D microscopic imaging and metrology. The virtual network computer (VNC) is introduced to remotely control the 3D microscopic imaging system. Data storage and management are handled through the open source project eSciDoc. Considering the security of remote laboratory, the fingerprint is used for authentication with an optical joint transform correlation (JTC) system. The phase-aided fringe projection 3D microscope (FP-3DM), which can be remotely controlled, is employed to achieve the 3D imaging and metrology of micro objects.

A newly developed measuring procedure uses vignetting to evaluate angles and angle changes, independently from the measurement distance. Further on, the same procedure enables the transmission of a digital readout and therefore a better automation of the electronic signal evaluation, for use as an alignment telescope. The fully extended readout by a simple 3-D reflector will provide the user with a measurement result with six degrees of freedom. The vignetting field stop procedure will be described. Firstly, considering artificial vignetting, the theoretical basics from geometric-optical view are represented. Secondly, the natural vignetting with photometric effects will be considered. The distribution of intensity in the image plane light spot, the so-called V-SPOT, is analytically deduced as a function of differently measured variables. Intensity shifts within the V-Spot are examined independently from different effects by numeric simulation. On these basics, the theoretical research regarding accuracy, linearity as well as results in 2 dimensional surface reconstruction on precision optical mirrors and also three dimensional measurements in mechanical engineering are examined. Effects and deviations will be discussed. The project WiPoVi is sponsored by “Ingenieur Nachwuchs – Qualifizierung von Ingenieurnachwuchs an Fachhochschulen” by Bavarian State Ministry of Education, Science and the Arts.

Scatterometry is a common tool for the dimensional characterization of periodic nanostructures. In this paper we compare measurement results of two different scatterometric methods: a goniometric DUV scatterometer and a coherent scanning Fourier scatterometer. We present a comparison between these two methods by analyzing the measurement results on a silicon wafer with 1D gratings having periods between 300 nm and 600 nm. The measurements have been performed with PTB’s goniometric DUV scatterometer and the coherent scanning Fourier scatterometer at TU Delft. Moreover for the parameter reconstruction of the goniometric measurement data, we apply a maximum likelihood estimation, which provides the statistical error model parameters directly from measurement data.

The fine polishing technique, e.g. Chemical Mechanical Polishing treatment (CMP), is one of the most important techniques in the glass substrate manufacturing. However, mechanical interaction, e.g. friction, occurs between the abrasive and the surface of substrates. Therefore, latent flaws are formed in the surfaces of glass substrates depending on the polishing condition. In the case of the cleaning process of the glass substrate in which the latent flaws existed, latent flaws become obvious because glass surfaces were eaten away by chemical interaction of cleaning liquid. Therefore, latent flaws are the cause of decrease the yield of products. In general, non-destructive inspection techniques, e.g. light scattering method, foreign matter on the surface of glass substrates. Though, it is difficult to detect the latent flaws by these method, because these are closed. The present authors propose a novel inspection technique of latent flaws which occurred by the fine polishing technique, using light scattering method with stress concentration (Stress-Induced Light scattering Method; SILSM). SILSM is possible to classify and separately detect latent flaws and particles on the surfaces. Samples are deformed by the actuator and stress concentrations are occurred around the tip of latent flaws. By photo-elastic effect, the refractive index of around the tip of latent flaws is changed. And then, changed refractive index is detected by cooled CCD camera as the light scattering intensity. In this report, applying SILSM to glass substrates, latent flaws on the surface of glass substrates are detected non-destructively, and the usefulness of SILSM is evaluated as novel inspection technique of latent flaws.

Scatterometry is a common technique for dimensional characterisation of nanostructures in the semiconductor industry. Currently this technique is limited to relative measurements for process development and process control. Although the high sensitivity of scatterometry is well known, it is not yet applied for absolute measurements of critical dimensions (CD) and quality control due to the lack of traceability. Thus we aim to establish scatterometry as traceable and absolute metrological method for dimensional measurements. Suitable high quality calibrated scatterometry reference standard samples are currently developed as one important step to enable traceable absolute measurements in industrial applications. The reference standard materials will base either on Si or on Si₃N₄. A traceable calibration of these standards will be provided by applying and combining different scatterometric as well as imaging calibration methods. First Silicon test samples have been manufactured and characterised for this purpose. The etched Si gratings have periods down to 50 nm and contain areas of reduced density to enable AFM measurements for comparison. We present the current design and first characterisations of structure details and the grating quality based on AFM measurements, optical, EUV and X-Ray scatterometry as well as spectroscopic ellipsometry. Finally we discuss possible final designs and the aimed specifications of the standard samples to face the tough requirements for future technology nodes in lithography.

In microelectronics the two crucial parameters for the lithography step are the critical dimension, which is the width of the smallest printable pattern, and the misalignment error of the reticle, called overlay. For the 14 nm node, the limit of scanner resolution can be overcome by the double patterning technique, which requires a maximum overlay error between the two reticles of 3 nm ^[1]. The current approach in the measurements of critical dimension and overlay is to treat them separately, but it has become much more complex in the double patterning context, since they are no longer independent. In this paper, a strategy of a common measurement is developed. The aim of the strategy is to measure simultaneously overlay and critical dimension in the metal level double patterning grating before the second etch process. The scatterometry technique is well known for critical dimension measurement. This study demonstrates that the overlay between the two gratings can also be deduced. Thanks to this original scatterometry-based method, it becomes possible to provide information on the lithography step quality before the second etch process; therefore the lithography can be reworked if it is necessary.

Polymer substrates which are covered with a thin layer of graphene nanoplatelets or carbon nanotubes have a big potential for modern engineering, especially in organic electronics. The main advantage of those materials is transparency in the visible part of the electromagnetic spectrum. This property creates a possibility of using these materials to produce electrodes in flexible screens and light sources. It is necessary to know the transmission characteristics of these materials to assess their usefulness in optoelectronics. In the article authors present the results of the conducted research on the transmittance characteristics of different samples. The samples contained different deposited substances. They had various diameters of the graphene nanoplatelets, one group contained carbon nanotubes. Samples had 50 or 100 layers. The authors examine the influence of these parameters on ink transmittance and ink transmittance uniformity. These analyses are a base for future research on flexible carbon electrodes, especially for applying them in production of flexible organic displays and light sources.

We use scanning near-field optical microscopy (SNOM) to characterize different plasmonic-nanoparticle situations with high spatial and spectral resolution in this comparative study. The near-field enhancement is measured with an aperture probe (Al coated glass fiber) and two CCD spectrometers for simultaneous detection of reflection and transmission. The images of transmission and reflection show a correlation to the topography. We present a new way to access the relative absorption and discuss the results with consideration of artifact influences. Near-field enhancements are deeper understood by imaging isolated particles. This near field will be compared to measurements of random-particle distributions. Therefore, we will show normalized reflection and transmission images of random structures that lay the foundation for an absolute interpretation of near-field images. The normalization considers both the far-field UV/VIS results and a reference image of the substrate. The near-field reflection of nanoparticle arrays shows an enhancement of 25 %. In view of specific applications, particle distributions implemented in two ways: as far-field scatters and as near field enhancing objects.

To investigate light propagation and near-field effects above structured surfaces, scanning near-field optical microscopy is a powerful tool providing access to the near-field intensity. These measurements can be combined with rigorous solving of Maxwell's equations to gain insight into light propagation inside the sample, which is not accessible via experiment. However, we find differences between the intensity distribution obtained via experiment and that observed in the simulation at a constant distance of 20 nm above the surface, which corresponds to the typical surface-to-probe distance in the experiment. A first explanation was given by topographic artefacts [Proc. SPIE 8789, 87890I (2013)]. To better understand the interaction between sample and probe in regard to light propagation, we include the probe in high-resolution simulations of different structures, with the position of the (finite-sized) probe resulting from its placement above each structure. While there is a visible difference in the overall light distribution of the system, caused by the probe, the relative intensity at the position of the probe is shown to be in very good agreement to the intensity in a system without the probe. This has been found for many probe positions along the surface of the structure. This result is applicable to many systems in different fields of research which use such measurements for obtaining information about near-field effects of samples. We show an application for thin-film photovoltaics, where light scattering textured surfaces are used to increase the path length of photons in the absorber layer to increase device performance.

Interferometric form testing using computer generated holograms is one of the main full-field measurement techniques. Till now, various modified measurement setups for optical form testing interferometry have been presented. Currently, typical form deviations in the region of several tens of nanometers occur in case of the widely used computer generated hologram (CGH) based interferometric form testing. Deviations occur due to a non-perfect alignment of the computer generated hologram (CGH) relative to the transmission sphere (Fizeau objective) and also of the asphere relative to the testing wavefront. Thus, measurement results are user and setup dependent which results in an unsatisfactory reproducibility of the form errors. In case of aligning a CGH, this usually requires a minimization of the spatial frequency of the fringe pattern by an operator. Finding the ideal position however often cannot be performed with sufficient accuracy by the operator as the position of minimum spatial fringe density is usually not unique. Therefore, the scientific and technical objectives of this paper comprise the development of a simulation based approach to explain and quantify the experimental errors due to misalignment of the specimen towards a computer generated hologram in an optical form testing measurement system. A further step is the programming of an iterative method to realize a virtual optimised realignment of the system on the basis of Zernike polynomial decomposition which should allow the calculation of the measured form for an ideal alignment and thus the subtraction of the alignment based form error. Different analysis approaches are investigated with regard to the final accuracy and reproducibility. To validate the theoretical models a series of systematic experiments is performed with hexapod-positioning systems in order to allow an exact and reproducible positioning of the optical CGH-based setup.

Sinusoidal optical path length modulation of the reference or the measurement arm of an interferometer is a technique which is a fast alternative to white light or phase shifting interferometry. In this paper three different sensors using this periodical modulation are presented. In addition, signal processing algorithms based on Discrete Fourier Transform, Hilbert Transform and parameter estimation are analyzed. These algorithms are used to obtain measurement results which demonstrate the capabilities of the presented interferometric sensors.

We report the development of a new device able to record an optical wavefront with an improved sensitivity and without resorting to any reconstruction technique such as Zernike polynomial decomposition. A direct comparison with a standard Shack-Hartmann sensor is performed within the field of Z-scan-like experiments. It is also shown using computer-generated holograms that our device is suitable for characterizing phase discontinuities or sharp phase variations.

Fringe projection 3D microscopy (FP-3DM) plays an important role in micro-machining and micro-fabrication. FP-3DM may be realized with quite different arrangements and principles, which make people confused to select an appropriate one for their specific application. This paper introduces the ray-based general imaging model to describe the FP-3DM, which has the potential to get a unified expression for different system arrangements. Meanwhile the dedicated calibration procedure is also presented to realize quantitative 3D imaging. The validity and accuracy of proposed calibration approach is demonstrated with experiments.

The presented paper shows the concept and optical design of an array-type Mirau-based OCT system for early diagnosis of skin cancer. The basic concept of the sensor is a full-field, full-range optical coherence tomography (OCT) sensor. The micro-optical interferometer array in Mirau configuration is a key element of the system allowing parallel imaging of multiple field of views (FOV). The optical design focuses on the imaging performance of a single channel of the interferometer array and the illumination design of the array. In addition a straylight analysis of this array sensor is given.

Optical diffraction tomography is an increasingly popular method that allows for reconstruction of three-dimensional refractive index distribution of semi-transparent samples using multiple measurements of an optical field transmitted through the sample for various illumination directions. The process of assembly of the angular measurements is usually performed with one of two methods: filtered backprojection (FBPJ) or filtered backpropagation (FBPP) tomographic reconstruction algorithm. The former approach, although conceptually very simple, provides an accurate reconstruction for the object regions located close to the plane of focus. However, since FBPJ ignores diffraction, its use for spatially extended structures is arguable. According to the theory of scattering, more precise restoration of a 3D structure shall be achieved with the FBPP algorithm, which unlike the former approach incorporates diffraction. It is believed that with this method one is allowed to obtain a high accuracy reconstruction in a large measurement volume exceeding depth of focus of an imaging system. However, some studies have suggested that a considerable improvement of the FBPP results can be achieved with prior propagation of the transmitted fields back to the centre of the object. This, supposedly, enables reduction of errors due to approximated diffraction formulas used in FBPP. In our view this finding casts doubt on quality of the FBPP reconstruction in the regions far from the rotation axis. The objective of this paper is to investigate limitation of the FBPP algorithm in terms of an off-axis reconstruction and compare its performance with the FBPJ approach. Moreover, in this work we propose some modifications to the FBPP algorithm that allow for more precise restoration of a sample structure in off-axis locations. The research is based on extensive numerical simulations supported with wave-propagation method.

Optical coherence tomography (OCT) is one of the most advanced optical measurement techniques for complex structure visualization. The advantages of OCT have been used for surface and subsurface defect detection in composite materials, polymers, ceramics, non-metallic protective coatings, and many more. Our research activity has been focused on timefrequency spectroscopic analysis in OCT. It is based on time resolved spectral analysis of the backscattered optical signal delivered by the OCT. The time-frequency method gives spectral characteristic of optical radiation backscattered or backreflected from the particular points inside the tested device. This provides more information about the sample, which are useful for further analysis. Nowadays, the applications of spectroscopic analysis for composite layers characterization or tissue recognition have been reported. During our studies we have found new applications of spectroscopic analysis. We have used this method for thickness estimation of thin films, which are under the resolution of OCT. Also, we have combined the spectroscopic analysis with polarization sensitive OCT (PS-OCT). This approach enables to obtain a multiorder retardation value directly and may become a breakthrough in PS-OCT measurements of highly birefringent media. In this work, we present the time-frequency spectroscopic algorithms and their applications for OCT. Also, the theoretical simulations and measurement validation of this method are shown.

In the paper the case of diffraction tomography with limited angle of projections is discussed from the experimental and algorithmic point of views. To reconstruct a 3D distribution of refractive index of an object under study, we use the hybrid approach, which enables to apply the standard Computer Tomography algorithms for phase data obtained by digital holography. We present the results of applying Simultaneous Algebraic Reconstruction Technique together with Anisotropic Total Variation minimization (SART+ATV) on both a phantom object and real data acquired from an experimental setup based on a Mach-Zehnder interferometer configuration. Also, the analysis of the influence of the limited number of projections within a limited angular range is presented. We prove that in the case of simulated data, the limited number of projections captured in a limited angular range can be compensated by higher number of iterations of the algorithm. We also show that SART+ATV method applied for experimental data gives better results than the popular Data Replenishment algorithm.

We analyze axial scanning in Confocal microscopy based on Adaptive Lenses (CAL). A tunable lens located in the illumination path of a confocal setup enables scanning the focus position by applying an electrical voltage. This opens up the possibility to replace mechanical axial scanning which is commonly used. In our proof-of-principle experiment, we demonstrate a tuning range of about 380 μm. The range can easily be extended by using the whole possible tuning range. During the scan the axial resolution degrades by a factor of about 2.3. The deterioration is introduced by aberrations that strongly depend on the scanning process. Therefore a second lens is located in the detection path of the CAL setup to balance the aberration effects. Both experiments and simulations show that this approach allows creating a homogeneous axial resolution throughout the scan. This is at the cost of tuning range which halves to about 200 μm. The lateral resolution is not noticeably affected and amounts to 500 nm.

Dedicated prototype systems for 3D imaging and modeling (3DIM) are presented. The 3D imaging systems are based on the principle of phase-aided active stereo, which have been developed in our laboratory over the past few years. The reported 3D imaging prototypes range from single 3D sensor to a kind of optical measurement network composed of multiple node 3D-sensors. To enable these 3D imaging systems, we briefly discuss the corresponding calibration techniques for both single sensor and multi-sensor optical measurement network, allowing good performance of the 3DIM prototype systems in terms of measurement accuracy and repeatability. Furthermore, two case studies including the generation of high quality color model of movable cultural heritage and photo booth from body scanning are presented to demonstrate our approach.

In comparison to classical phase measurement methods like interferometry and holography, there are many phase retrieval methods which are able to recover the phase of a complex valued object without the necessity of a reference wave. Due to the large number of different methods, iterative as well as non-iterative ones, it is hard to find the method which is appropriate for a given application or object. We propose a system which is based on different criteria, some of which can be calculated by analyzing the phase retrieval result compared to the original object. Other criteria like the complexity of the optical system are also taken into account. For testing the benchmark system we use a software which is suitable, first, to simulate the acquisition process of the intensity measurements, second, to run the phase retrieval algorithm itself and, third, to calculate the values of the benchmark criteria. Having determined the values of the different criteria we assign points for every criterion which can be weighted by importance and are summed up for getting an overall benchmark score. This final score can be used to compare different phase retrieval methods and by having a closer look at the single criteria it is possible to analyze the strengths and weaknesses of the method. We will show the detailed proceeding of calculating the benchmark value by means of a selected phase retrieval method and a phase only object (USAF target). We have to emphasize that the results strongly depend on the object.

The detection of a transparent object is a technical challenge since phase objects yield only poor contrast if they are imaged on an intensity basis. For performing quantitative measurement the image contrast has to be enhanced. For that, we can exploit additional information on phase or polarisation modifications of the laser probe beam (LPB) crossing through the phase object. We propose a simple method for determining the size of a transparent object based on the reshaping of a laser probe beam which is initially Gaussian in shape. For a given ratio between the size of the incident beam and that of the phase object, the diffracted laser probe beam is transformed in the far-field region into a hollow beam. The detection of the intensity dip in the beam centre is made with a simple photodiode. In practice, the spatial reshaping of the LPB is monitored through the resulting changes in the power transmitted by a pinhole and a stop (opaque disk) set in the far-field of the phase object under study. For convenience, the latter in the experiment is realised by a Spatial Light Modulator (SLM: Holoeye Pluto-NIR). We have considered the influence of various parameters which are the lateral and longitudinal sizes of the phase object, and the pinhole and the stop distances from the phase object under study. The experiment has demonstrated the feasibility of our method and can be extended for the detection of microscopic phase objects. The potential of the proposed technique for quantifying the nanoscale change of the phase object under study could be very useful to study the morphology dynamics of living cells membrane which represents the biophysical properties and health state of the cell.

The Transport of Intensity Equation (TIE) relates linearly the phase of an object to the intensity distribution in the Fresnel region and can be used as a phase retrieval technique. The key element in a TIE based solver is the calculation of the axial intensity derivative. This parameter is calculated from a series of captured intensities but its accuracy is subject to several parameters, such as e.g. the separation between the measurement planes, the Signal to Noise Ratio (SNR) in the captured intensities, the actual object phase distribution. Despite the importance of the estimation of this parameter, there is no general discussion how to optimize the axial intensity derivative. In this work, we developed the mathematical framework in which the retrieved phase can be obtained. An optimal separation is derived, which minimizes the error in the calculation of the axial derivative. Besides this, we study using a numerical analysis how the accuracy of the axial derivative influence the accuracy of the retrieved phase. Hence, we present a numerical procedure based in the Root Square Mean Error, which is able to minimized the error in the retrieved phase. It is later shown that this analysis is significant more accurate than available methods proposed in the literature. It is further shown, that the plane separation that minimizes the error in the axial intensity derivative is different to the plane separation that minimizes the error in the retrieved phase.

Holography uses wave (physical) optical principles of interference and diffraction to record and display images. Interference allows us to record the amplitude and phase of the optical wave emanating from an object on a film or recording medium and diffraction enables us to see this wave-field, i.e. the amplitude and phase of the object. Visually this corresponds to both perspective and depth information being reconstructed as in the original scene. Digital Holography has enabled quantification of phase which in some applications provides meaningful engineering parameters. There is growing interest in reconstructing this wavefield without interference. Thus the non-interferometric Transport of Intensity Equation (TIE) method is gaining increased research, which uses two or more defocused images to reconstruct the phase. Due to its non-interferometric nature, TIE relaxes the stringent beam-coherence requirements for interferometry, extending its applications to various optical fields with arbitrary spatial and temporal coherence. The alternate school of thought emerges from the computer science community primarily deals with ray optics. In a normal imaging system all rays emerging from an object point into are focused to a conjugate image point. Information of ray direction is lost and thus the perspective and depth information. A light field image is one that has information of both amplitude and direction of rays fanning from any object point and thus provides perspective (or what could be termed as phase) of the object wave as well. It would thus be possible to extract phase as we know it from this albeit for a coherent illumination case.

Interferometric surface measurement of parallel plates presents considerable technical difficulties owing to multiple beam interference. To apply the phase-shifting technique, it is necessary to use an optical-path-difference-dependent technique such as wavelength tuning that can separate interference signals in the frequency domain. In this research, the surface shape and optical thickness variation of a lithium niobate wafer for a solid Fabry-Perot etalon during the polishing process were measured simultaneously using a wavelength-tuning Fizeau interferometer with a novel phase shifting algorithm. The novel algorithm suppresses the multiple beam interference noise and has sidelobes with amplitudes of only 1% of that of the main peak. The wafer, which was in contact with a supporting glass parallel plate, generated six different interference fringes that overlapped on the detector. Wavelength-tuning interferometry was employed to separate the specific interference signals associated with the target different optical paths in the frequency domain. Experimental results indicated that the optical thickness variation of a circular crystal wafer 74 mm in diameter and 5-mm thick was measured with an uncertainty of 10 nm PV.

In this investigation, we describe a technique to obtain the 3D profile of surface, thickness and refractive index of an undoped double-side polished Si wafer at once. This technique is based on low coherence scanning interferometry (LCSI) and spectrally-resolved interferometry (SRI) using a NIR light, which is around 1 μm, for which transmission is non-zero for undoped silicon and also detectable by the typical visible CCD camera. LCSI allows for the measurements of surface, thickness and refractive index profiles of the Si wafer while SRI can determine their nominal values. For group refractive index measurements, the target which consists of a Si wafer segment and a mirror was designed. Consequently, the combination of these two techniques with the target enables to measure surface, thickness and refractive index profiles simultaneously and accurately. In the experiments, an undoped double sided polished (DSP) Si wafer with 475 μm thickness was measured and the 3D profiles of optical thickness, geometrical thickness, group refractive index were successfully obtained. Because of not using an expensive IR CCD camera and an optical source, the proposed technique is cost-effective.

Over the past years, many applications based on laser-induced refractive index changes in the volume of transparent materials have been demonstrated. Ultrashort pulse lasers offer the possibility to process bulky transparent materials in three dimensions, suggesting that direct laser writing will play a decisive role in the development of integrated micro-optics. At the present time, applications such as 3D long term data storage or embedded laser marking are already into the phase of industrial development. However, a quantitative estimate of the laser-induced refractive index change is still very challenging to obtain. On another hand, several microscopy techniques have been recently developed to characterize bulk refractive index changes in-situ. They have been mostly applied to biological purposes. Among those, spatial light interference microscopy (SLIM), offers a very good robustness with minimal post acquisition data processing. In this paper, we report on using SLIM to measure fs-laser induced refractive index changes in different common glassy materials, such as fused silica and borofloat glass (B33). The advantages of SLIM over classical phase-contrast microscopy are discussed.

The absorption cells - optical frequencies references – represent the crucial part of setups for practical realization of the meter unit – highly stable laser standards, where varied laser sources are frequency locked to the selected absorption transitions. Furthermore, not only in the most precise laboratory instruments, but also in less demanding interferometric measuring setups the frequency stabilization of the lasers throught the absorption in suitable media ensure the direct traceability to the fundamental standard of length. We present the results of measurement and evaluation of spectral properties of molecular iodine absorption cells filled to saturation pressure of absorption media. A set of cells filled with different amounts of molecular iodine was prepared and an agreement between expected and resulting spectral properties of these cells was observed and evaluated. The cells made of borosilicate glass instead of common fused silica were tested for their spectral properties in greater detail with special care for the absorption media purity – the measured hyperfine transitions linewidths were compared to cells traditionally made of fused silica glass with well known iodine purity. The usage of borosilicate glass material represents easier manufacturing process and also significant costs reduction but a great care must be taken to control/avoid the risk of absorption media contamination. An approach relying on measurement of linewidth of the hyperfine transitions is proposed and discussed.

Diffraction efficiency and image processing enhanced two-dimensional Talbot shearing interferometry providing phase object derivative information in two mutually orthogonal directions is proposed. The properties of the Talbot interferometer using amplitude checker grating are studied and its performance is compared with a common configuration based on the cross-type amplitude Ronchi grids. Besides the light output gain further setup attractiveness is related to conducting the automatic fringe pattern analysis guided by recently introduced Hilbert-Huang processing for single exposure two-dimensional grating interferometry. The checker grating self-image deformed by the object under test is resolved into two linear fringe families running in 45/135 deg directions with respect to checker grating lines. Next the separated fringe sets are filtered using automatic selective reconstruction aided by enhanced fast empirical mode decomposition and mutual information detrending. Finally the Hilbert spiral transform is implemented to retrieve phase maps representing first derivatives of the object phase distribution. Efficient adaptive digital filtering enables analysis of complex patterns without resorting to coherent spatial filtering resulting in complicated and bulky experimental setups. Numerical and experimental studies corroborate the robustness and versatility of the proposed approach.

We present a measuring technique for displacement and position sensing over a limited range with detection of standingwave pattern inside of a passive Fabry-Perot cavity. The concept considers locking of the laser optical frequency and the length of the Fabry-Perot cavity in resonance. Fixing the length of the cavity to e.g. a highly stable mechanical reference allows to stabilize wavelength of the laser in air and thus to eliminate especially the faster fluctuations of refractive index of air due to air flow and inhomogeneities. Sensing of the interference maxima and minima within the cavity along the beam axis has been tested and proven with a low loss photoresistive photodetector based on a thin polycrystalline silicon layer. Reduction of losses was achieved thanks to a design as an optimized set of interference layers acting as an antireflection coating. The principle is demonstrated on an experimental setup.

Derived from Spectral Interferometry, a line sensor named Laterally Chromatically Dispersed, Spectrally Encoded Interferometer has been developed lately. The basic setup features a single SLD in the near infra-red range, whose light is laterally spread over a measurement line of about 1mm by a diffraction grating. The signal encodes the lateral position as well as the respective optical path difference for every pixel on the spectrometer. Thus, an elaborated evaluation strategy is needed for precise measurement, including the need for a priori knowledge of the surface or multiple related measurements. To overcome this limitation and provide a real single-shot measurement, the setup can be extended by a second light source. However, the sources have to meet some strong requirements, such as sufficient spectral separation. Sensor simulations for different classes of objects show, that an accurate reconstruction of many surfaces can be achieved with the extended setup in a real single-shot line measurement without the need for a priori information.

We present a method of noise suppression of laser diodes by unbalanced Michelson fiber interferometer. The unstabilized laser source is represented by compact planar waveguide external cavity laser module ORION (Redfern Integrated Optics, Inc.) working at 1040.57 nm with < 3 kHz linewidth. We built Michelson interferometer with 1 km long arm based on SMF-28 fiber spool to suppress the frequency noise by fast PI servo-loop up to 33 kHz of laser injection current modulation. We were able to decrease the noise level by −60 dBc/Hz up to 1.5 kHz noise frequency of the laser.

The laser-diode self-mixing technique is a well-known, powerful, very simple and low cost interferometric technique. The typical structure of a laser-diode self-mixing device is made up of a laser-diode, a focusing lens and a processing unit. One can find in literature numerous examples of target displacement, fluid flow, velocity, distance and vibration measurements. Regarding vibration measurements, the self-mixing effect has been mainly applied to measure amplitude and frequency in isolated points but it is difficult to find real applications in which this technique is applied to measure the vibrating behavior of a complete surface. This is due to the different feedback signals that may appear when a laser beam is scattered by a real rough surface. When scanning a surface, the different speckle patterns that contain the feedback signal at different points introduce big changes in the intensity of the scattered signal captured by the photodiode that drives the laser into a strong coupling self-mixing regime with loss of the sinusoidal behavior of the fringes. In many cases, saturation of the photodiode is also found. When this occurs, it is not possible to measure any vibration parameter. By programming simple algorithms, this problem can be overcome. Here we present vibration measurements of titanium tweeter membranes up to 6.8 Khz that show the vibrating behavior in the micrometer range. We demonstrate that the limit in the frequency range is set by the sample frequency of the data acquisition device. Results are compared with different optical techniques for mapping vibrating surfaces such as laser triangulation and electronic speckle pattern interferometry.

Measurement of a wafer thickness is of a great value for fabrication and interrogation of MEMS/MOEMS devices, as well as conventional optical fiber sensors. In the current paper we investigate the abilities of the wavelength-scanning interferometry techniques for registering the baseline of an extrinsic fiber Fabry-Perot interferometer (EFPI) with the cavity formed by the two sides of a silicon plate. In order to enhance the resolution, an improved signal processing algorithm was developed. Various experiments, including contact and non-contact measurement of a silicon wafer thickness were performed, with the achieved resolutions from 10 to 20 pm. This enables one to use the described approach for high-precision measurement of geometric parameters of micro electro (electro-optic) mechanical systems for their characterization, utilization in sensing tasks and fabrication control. An ability of a Si plate-based EFPI interrogated by the developed technique to capture temperature variations of about 4 mK was demonstrated.

In this study, we proposed and fabricated optical sensor module integrated onto optical-electrical printed circuit board (PCB) for gas detection based on polymer waveguide with tin oxide thin film. Their potential application as gas sensors are confirmed through computational simulation using the two dimensional finite-difference time-domain method (2DFDTD). Optical-electrical PCB was integrated into vertical cavity surface emitting laser (VCSEL), photodiode and polymeric sensing device was fabricated by the nano-imprint lithography technique. SnO₂ thin film of 100nm thickness was placed on the surface of core layer exposed by removing the specific area of the upper cladding layer of 300 μm length and 50 μm width. The performance of the device was measured experimentally. Initial study on the sensor performance for carbon monoxide gas detection indicated good sensitivity.

High-resolution miniature imaging systems require high quality micro-optical elements. Therefore, it is essential to characterize their optical performances in order to optimize their fabrication. Usually, basic evaluation of micro-optical elements quality is based on the measurement of their topography since their optical properties are largely defined by their shape. However, optical characteristics have to be derived from the measured geometry. An alternative method is the direct measurement of their optical properties. Unlike topography measurement, it allows characterization of high numerical aperture components. Moreover, it can be applied to single elements but also to optical systems composed of several micro-optical components. In this work, we propose a simple method based on the measurement of the 3D intensity point spread function (IPSF). IPSF is defined by the 3D shape of the focal spot generated by the micro-element. The direct characterization of focusing response through the measurement of IPSF allows very precise estimation of micro-structures quality. The considered method consists in imaging different slices of the focal volume generated by the focusing component. It allows, depending on the configuration, characterizing both transmissive and reflective micro-optical components.

In this work, we present a detailed experimental Raman investigation of nanostructured silicon films prepared by metalassisted chemical etching with different nanocrystal sizes and structures. Interpretation of observed one and two-phonon Raman peaks are presented. First-order Raman peak has a small redshift and broadening. This phenomenon is analyzed in the framework of the phonon confinement model. Second-order Raman peaks were found to be shifted and broadened in comparison to those in the bulk silicon. The peak shift and broadening of two-phonon Raman scattering relates to phonon confinement and disorder. A broad Raman peak between 900-1100 cm^-1 corresponds to superposition of three transverse optical phonons ~2TO (X), 2TO (W) and 2TO (L). Influence of excitation wavelength on intensity redistribution of two-phonon Raman scattering components (2TO) is demonstrated and preliminary theoretical explanation of this observation is presented.

Scanning white light interferometry (SWLI) is an established methodology for non-destructive testing of MEMS/NEMS. In contrast to monochromatic interference microcopy SWLI can unambiguously resolve surfaces featuring tall vertical steps. Oscillating samples can be imaged using a stroboscopic SWLI (SSWLI) equipped with a pulsed light source. To measure static samples the lateral and vertical scales of the SSWLI can be calibrated using transfer standards with calibrated dimensions such as line scales, 2D gratings, gauge blocks, and step height standards. However, traceable dynamic characterization of SSWLI requires a transfer standard (TS) providing repeatable traceable periodic movement. A TS based on a piezo-scanned flexure guided stage with capacitive feedback was designed and manufactured. The trajectories of the stage motion for different amplitude and frequency settings were characterized to have ~2 nm standard uncertainty. Characterization was made using a symmetric differential heterodyne laser interferometer (SDHLI). The TS was first used to characterize quasidynamic measurements across the vertical range of the SSWLI, 100 μm. Dynamic measurement properties of the SSWLI were then characterized using a sinusoidal vertical trajectory with 2 μm nominal amplitude and 50 Hz frequency. The motion amplitude of the TS, 2038 nm, measured with the SSWLI was 6 nm smaller than the amplitude measured with SDHLI. The repeatability of SSWLI expressed as experimental standard deviation of the mean was 8.8 nm. The maximum deviation in instantaneous displacement and oscillation velocity were 49 nm and 27 μm/s, respectively. A traceable method to characterize the capacity of the SSWLI to perform dynamic measurements at sub-kHz frequencies was demonstrated.

Based on a miniature digital light projector (pico-DLP), a prototype of a Structured Illumination Microscope (SIM) has been developed. The pico-DLP is used to project fringes onto a sample and applying the three-step phase shifting algorithm together with the absolute phase retrieval method, the 3D shape of the object surface is extracted. By using a specific optical system instead of a conventional microscope objective, the device allows 3D reconstructions of surfaces with both a 10× magnification and a high depth of field obtained thanks to a small numerical aperture of 0.06 offering an acceptable lateral resolution of 6.2 μm. An image processing algorithm has been developed to reduce the noise in the acquired images before applying the reconstruction algorithm and so optimize the reconstruction method. Compared with interference microscopy and confocal microscopy that have a shallower depth of field per XY image, the microscope developed achieves a depth of field about 700 μm and requires no vertical scanning, which greatly reduces the acquisition time. Although the system at this stage does not have the same resolution performance as interference microscopy, it is nonetheless faster and cheaper. One possible application of this SIM technique would be to first reconstruct in real-time parts of an object before performing higher resolution 3D measurements with interference microscopy. As with all classical optical instruments, the lateral resolution is limited by diffraction. Work is being carried out with the prototype SIM system to be able to exceed the lateral resolution limits and thus achieve super resolution.

Fe’s optical and electronic properties were investigated at room temperature in different structural states. The sample’s surface was explored in wide spectral range λ = 0,23−17,0 μm (E = 4,96 − 0,07 еV ) by the Beatty’s spectral ellipsometry method. While an experiment was carried out ellipsometry parameters Δ and ψ were measure near the principal angle of incidence. The refraction index R , permittivity Ɛ and optical conductivity σ( hν ) , that is proportional to the interband density of electronic states, were calculated using these parameters. Fe’s optical conductivities in liquid, amorphous and crystalline states were compared in this work. The optical conductivity was calculated using the published data of the iron’s density of electronic states in crystalline, amorphous and liquid states for the comparison of the experimental and theoretical results. It is shown that, at structural transformations “amorphous, liquid state– crystalline state”, the optical properties of metallic iron are determined, in the first turn, by the nearest neighborhood, and the electronic structure is not subjected to significant modifications.

We present a fingerprint authentication scheme based on the optical joint transform correlator (JTC) and further describe its application to the remote access control of a Network-based Remote Laboratory (NRL). It is built to share a 3D microscopy system of our realistic laboratory in Shenzhen University with the remote co-researchers in Stuttgart University. In this article, we would like to focus on the involved security issues, mainly on the verification of various remote visitors to our NRL. By making use of the JTC-based optical pattern recognition technique as well as the Personal Identification Number (PIN), we are able to achieve the aim of authentication and access control for any remote visitors. Note that only the authorized remote visitors could be guided to the Virtual Network Computer (VNC), a cross-platform software, which allows the remote visitor to access the desktop applications and visually manipulate the instruments of our NRL through the internet. Specifically to say, when a remote visitor attempts to access to our NRL, a PIN is mandatory required in advance, which is followed by fingerprint capturing and verification. Only if both the PIN and the fingerprint are correct, can one be regarded as an authorized visitor, and then he/she would get the authority to visit our NRL by the VNC. It is also worth noting that the aforementioned “two-step verification” strategy could be further applied to verify the identity levels of various remote visitors, and therefore realize the purpose of diversified visitor management.

For the purpose of nondestructive determination of the mechanical properties of nano-scale materials including nanowires, nanoparticles, etc., an extended AFM-based materials testing method, the contact resonance force microscopy (CR-FM), is applied. This CR-FM method features high lateral (dimensional) resolution and low test force (down to subnanonewton). It can be employed for not only hard materials, but also soft materials or weak structures, like silicon nano-pillars. In this method, the elastic material properties are deduced by experimental measurement of the resonance frequency shift of an AFM cantilever before and after mechanical contact with the specimen under test. Numerical and analytical investigations of the key issues of this method, including (1) body stiffness of nanopillars, (2) tip-surface mechanical interaction and (3) theoretical measurement resolution, have been carried out, in order to prepare the design and the development of the experimental system. To improve the measurement uncertainty of this method, a MEMSbased cantilever stiffness calibration approach and an interferometric cantilever deflection measurement system have been developed.

We have addressed the challenge to carry out the angular tilt stabilization of a laser guiding mirror which is intended to route a laser beam with a high energy density. Such an application requires good angular accuracy as well as large operating range, long term stability and absolute positioning. We have designed an instrument for such a high precision angular tilt measurement based on a triangulation method where a laser beam with Gaussian profile is reflected off the stabilized mirror and detected by an image sensor. As the angular deflection of the mirror causes a change of the beam spot position, the principal task is to measure the position on the image chip surface. We have employed a numerical analysis of the Gaussian intensity pattern which uses the nonlinear regression algorithm. The feasibility and performance of the method were tested by numeric modeling as well as experimentally. The experimental results indicate that the assembled instrument achieves a measurement error of 0.13 microradian in the range ±0.65 degrees over the period of one hour. This corresponds to the dynamic range of 1:170 000.

Stacks of metal plates are widely used in electrical motors, transformers and generators to reduce for eddy current loss in their magnetic circuit. To model the mechanical behavior of such special material structures a profound knowledge of the underlying physical processes is needed. This paper describes a highly specialized optical sensor system utilizing the laser-speckle-effect for non-contacting strain and displacement measurements of stacked metal plates. In order to gain insights into the mechanical changes of stacked metal structures during defined mechanical load, a certain kind of spatially resolving digital laser speckle photography has been used to measure displacements between individual layers of the stacked metal sheets at high resolution. The developed speckle template matching algorithm takes into account for the very special surface structure and the given loading behavior. The sensor system is capable of acquiring displacement fields with a resolution in the order of a single micron at video rate and beyond, enabling the real time observation of load experiments on stacked metal plate structures.

Free-standing thin membranes have now been widely applied in various research and industrial fields. As one of the key parameters of thin membranes, the membrane thickness is demanded to be precisely determined. A traceable membrane thickness measurement system is presented in this paper. It utilizes a pair of micro-machined nano-force transducers to actively detect both surfaces of a free-standing micro-machined membrane. Thanks to the high force sensitivity (down to a few Nanonewton) and a relatively large movement range (up to 10 μm) of the MEMS transducers in use, the proposed thickness measurement micro-system is capable of measuring membranes with small open aperture and membrane thicknesses down to sub-100 nm. In addition, the in-plane movement of the MEMS-transducers is measured in real-time by a single-frequency laser interferometer with nanometric resolution, which is traceable to the SI unit. Numerical analysis of the tip-membrane mechanical contact at nano-scale has been undertaken, which guides the selection of appropriate stylus radius used for experiments. Design and construction of the miniature thickness measurement system are detailed in this paper, including the first measurement results, which prove the feasibility of the proposed measurement system.

Digital holography (DH) is a well-established interferometric tool in optical metrology allowing the investigation of engineered surface shapes with microscale lateral resolution and nanoscale axial precision. With the advent of charged coupled devices (CCDs) with smaller pixel sizes, high speed computers and greater pixel numbers, DH became a very feasible technology which offers new possibilities for a large variety of applications. DH presents numerous advantages such as the direct access to the phase information, numerical correction of optical aberrations and the ability of a numerical refocusing from a single hologram. Furthermore, as an interferometric method, DH offers both a nodestructive and no-contact approach to very fragile objects combined with flexibility and a high sensitivity to geometric quantities such as thicknesses and displacements. These features recommend it for the solution of many imaging and measurements problems, such as microelectro-optomechanical systems (MEMS/MEOMS) inspection and characterization. In this work, we propose to improve the performance of a DH measurement on MEMS devices, through digital filters. We have developed an automatic procedure, inserted in the hologram reconstruction process, to selectively filter the hologram spectrum. The purpose is to provide very few noisy reconstructed images, thus increasing the accuracy of the conveyed information and measures performed on images. Furthermore, improving the image quality, we aim to make this technique application as simple and as accurate as possible.

TIRDHM is a technique that allows to analyse the phase change of microscopical sections produced on the prism surface due to material attached on the top. Therefore, due to the evanescence waves properties we can analyse quantitatively the properties and specific morphology located to few nanometers on the top of surface contact. In this work, we study and present an alternative method to off-axis configuration to record and analyse the microscopical phase object information in Total Internal Reflection dispensing with the use of reference arm.

This paper presents a method for active angular alignment of gauge block implemented in a system for automatic contactless calibration of gauge blocks designed at ISI ASCR. The system combines low-coherence interferometry and laser interferometry, where the first identifies the gauge block sides position and the second one measures the gauge block length itself. A crucial part of the system is the algorithm for gauge block alignment to the measuring beam which is able to compensate the gauge block lateral and longitudinal tilt up to 0.141 mrad. The algorithm is also important for the gauge block position monitoring during its length measurement.

We propose to extend the principle of compensation of the fluctuations of the refractive index of air through monitoring the optical length within the measuring range of the displacement measuring interferometer. The concept is derived form a tracking refractometry evaluating the refractive index of air in the beam axis coinciding with the positioning interferometer. Application of this approach in multi-axis positioning and measurement mans to compromise the principle of spatial unity of the displacement measuring laser beam and the beam of the tracking refractometer. In this contribution we evaluate the level of uncertainty associated with the spatial shift of these two beams. Consequently the nature of the fluctuations of the refractive index of air in laser interferometry is investigated and discussed with the focus on potential applications in coordinate measuring systems and long-range metrological scanning probe microscopy systems.

Frequency Scanning Interferometry(FSI) generally results in superior optical performance comparing with other 3-dimensional measuring methods as its hardware structure is fixed in operation and only the light frequency is scanned in a specific spectral band without vertical scanning of the target surface or the objective lens. However, it still suffers from optical noise due to polarization characteristic of target surfaces and relatively long processing time due to the number of images acquired in frequency scanning phase. First, a Polarization-based Frequency Scanning Interferometry(PFSI) is proposed for optical noise robustness. It consists of tunable laser for light source, λ/4 plate in front of reference mirror, λ /4 plate in front of target object, polarizing beam splitter, polarizer in front of image sensor, polarizer in front of the fiber coupled light source, λ/2 plate between PBS and polarizer of the light source. Using the proposed system, we can solve the problem of fringe image with low contrast by using polarization technique. Also, we can control light distribution of object beam and reference beam. Second the signal processing acceleration method is proposed for PFSI, based on parallel processing architecture, which consists of parallel processing hardware and software such as Graphic Processing Unit(GPU) and Compute Unified Device Architecture(CUDA). Finally, the proposed system is evaluated in terms of accuracy and processing speed through a series of experiment and the obtained results show the effectiveness of the proposed system and method.