Industry frequently demands fast and robust measurement techniques for the inline inspection of the full shape of objects in the micro range. We present a method for complete 360 degree measurement of the shape of a micro cup using digital holographic microscopy and show first results of sequential 360 degree measurement using different illumination and observation directions.

The deformation measurement method by using only two speckle pattern has been proposed in ESPI by using Fourier transform. Speckle interferometry can measure not only the out-of-plane but also the in-plane deformation measurement of the objects with rough surfaces. So, speckle interferometry is useful optical measurement method in the analysis of buckling phenomenon that occurs simultaneously in-plane and out-of-plane deformations in a beam. Generally, the inplane deformation can be detected by using the two-beam speckle interferometer. At present, some methods of 3-D deformation measurements have been also reported using some special speckle interferometers based on two-beam interferometer. Then, Fourier transform and the technologies based on digital holography were employed there. In these reports, some sets of the two-beam speckle interferometer are combined for 3-D deformation measurement. However, there are some problems. In this paper, a novel in-plane and out-of-plane deformation measurement optical system is proposed by combining one pair of interferometers under the idea based on the principle of two-beam interferometer. Then, the novel optical system is applied to the analysis of the buckling phenomena. The availability of the proposed method in the analyzing process of buckling phenomena is discussed with Euler’s buckling theory. From the experimental results, it can be confirmed that the buckling analysis of the beam agrees very well with the theory of Euler’s buckling.

We review new algorithms that have been presented by us lately¹ for fast reconstruction and phase unwrapping of sample wave-fronts recorded using off-axis digital holographic imaging. These algorithms enable reconstruction and phase unwrapping of sample wave-fronts up to 16 times faster than the conventional Fourier-based reconstruction algorithm. The algorithms exploit the compression properties of holographic imaging for decreasing the calculation complexity required for extracting the sample wave-front from the recorded interferogram. Using the presented algorithms, we were able to reconstruct, for the first time, 1 Mega pixels off-axis interferograms in more than 30 frames per second using a standard single-core personal computer on a Matlab-Labview interface, without using a graphic processing-unit programming or parallel computing. This computational speedup is important for real-time visualization, calculation and data extraction for dynamic samples and processes that are evaluated using off-axis digital holography such as biological cell imaging and real-time nondestructive testing.

In an on line shape measurement in disturbed environment, use of many wavelengths in order to avoid phase ambiguity may become a problem as it is necessary to acquire all holograms simultaneously due to environmental disturbances. Therefore to make the shape data available the different holograms have to be extracted from a single recorded image in spectral domain. Appropriate cut areas in the Fourier method are therefore of great importance for decoding information carried by different wavelengths. Furthermore using different laser sources, induces aberration and pseudo phase changes which must be compensated. To insure any phase change is only because of the object shape, calibration is therefore indispensable. For this purpose, effects of uncontrolled carrier frequency filtering are discussed. A registration procedure is applied using minimum speckle displacements to find the best cut area to extract and match the interference terms. Both holograms are numerically propagated to a focus plane to avoid any unknown errors. Deviations between a reference known plate and its measurement are found and used for calibration. We demonstrate that phase maps and speckle displacements can be recovered free of chromatic aberrations. To our knowledge, this is the first time that a single shot dual wavelength calibration is reported by defining a criteria to make the spatial filtering automatic avoiding the problems of manual methods. The procedure is shown to give shape accuracy of 35μm with negligible systematic errors using a synthetic wavelength of 1.1 mm.

We propose a single shot and single wavelength phase imaging technique for measuring phase of the transparent objects without using unwrapping process. A grating between a laser and the object is used to make beams with different angle, which determines the measurement range of the microscope. The grating pitch and magnification of the lens system before the sample affect the angle. The angle inside the object is changed according to Snell’s law; therefore, final angle is related to the refractive index of the object. Magnification of the lens system after sample will control the modulation frequency of microscope. The interference pattern is constructed at CCD plane and convey information of the sample. For a phase below the measurement range of the microscope, the reconstructed phase is not wrapped. By increasing the measurement range accuracy of the system will drop; therefore the magnification of the lenses must choose carefully to obtain optimal phase. The ability of this technique is demonstrated by reconstructing phases of two transparent step objects with 150 and 510 μm height. Their refractive indexes for red light are 1.515 and 1.508 , respectively. Therefore, total optical path length difference is 336 micrometers that is 500 times more than the laser wavelength. The phase is successfully reconstructed without using unwrapping algorithms.

Interferometric phase microscopy (IPM) is a quantitative optical imaging method for capturing the phase profiles of thin samples. While being an invaluable tool for biological and medical research, most IPM setups are unfriendly for inexperienced users, and have limited field of view (FOV). To overcome the limited FOV problem, it is possible to scan the sample and record a wider FOV. However, dynamic samples might move by the time the scan is over. Here, we review our previously published work presenting a new quantitative imaging technique, referred to as interferometry with tripled-imaging area (ITIA), which is capable of capturing three off-axis interferometric fields of view in a single camera exposure, thus tripling the acquired information without the need to scan the sample, without decreasing the image resolution, and without changing the system magnification. Our experimental demonstrations were done by using an inverted transmission microscope illuminated by a Helium-Neon laser. The sample is projected onto the image plane at the output of the microscope, where the ITIA module is placed. Various biological and non-biological samples were imaged.

Fabry-Perot displacement interferometry (FPI) offers high sensitivity and resolution with direct traceability to optical frequency standards. FPI can provide means for demanding calibration tasks in precision engineering and high-tech systems. We report on our investigation of the measurement methodology applied to highest precision capacitive displacement sensors. We use a dedicated metrological FPI instrumentation that provides an actuated reference target with a relatively large traceable displacement stroke. The envisaged sub-nanometer measurement uncertainty seems very challenging under practical ambient atmospheric conditions and with the necessary sensor mounting components. In anticipation of these limitations, we propose a new FPI instrumental configuration with a very short cavity and discuss expected benefits, most importantly the very low sensitivity to air refractive index variations and the versatility for practical calibration purposes. We aim again for sub-nanometer measurement uncertainty and report on the status of the experimental set-up for this short cavity FPI.

We demonstrate a method for determining the principal indices of refraction and the thickness of a birefringent wafer. Simply, the light transmittance was measured while rotating the wafer. The directly transmitted beam makes interference with those multiply reflected between the surfaces as in a Fabry-Pérot etalon, producing an interferogram as a function of angle of incidence. We applied this method to a LiNbO₃ wafer, determining the absolute values of ordinary and extraordinary indices with an uncertainty of 10^-5. In addition to the measurement accuracy, the major advantages of our method are extreme simplicity and environmental robustness in the experiment.

Interferometric system for detecting radiation wavelength shift functions based on a Fabry-Perot interferometer. Means developed for enhancing the system performance are described, namely: a method of increasing illumination of detected fringes for enhancing the system sensitivity, and a method of compensating interference maxima spreading caused by misalignment of mirrors that allows enhancing accuracy of light frequency shift measurement. The way to increase detected fringe brightness is based on additional reduction of the divergence of passing through the interferometer light beam. This method allows compensating negative effect of collimating lens spherical aberrations, and, using them, increasing the detector illumination. The way of compensating the interferometer mirrors misalignment effect on the detected fringe is based on use of specific relative position of beams from various parts of the interferometer near the focal plane of the focusing lens.

In this article we discuss a special operation regime of mode-mode interferometer under selective coherent and continuous excitation of multimode fiber in which number of modes increases along the waveguide. Experimental investigations which demonstrated signal dependencies from number of mode groups propagating at the point of perturbation were carried out. Theoretical model was also developed. The results of the work can be fundamental for a new solution of localization task for distributed optical fiber sensors based on mode-mode interference in multimode optical fiber.

Nondestructive testing of objects is the basis for quality control in a production line. There exists a wide range of optical and tactile methods for the detection of surface defects. For hidden defects (below the surface) different methods like Xray or ultrasound are state of the art; also, optical methods like thermography and interferometry can be used in combination with a load. This load can be mechanical, electrical or thermal and is used to produce a measurable signal (deviation of the surface, thermal signature) on the surface. Typically, the surface or the surface gradient of a specimen in a loaded and an unloaded state is measured and the two results are compared afterwards or in real time. The evaluation of shape differences is easier than measuring absolute shapes because systematic errors (e.g. calibration) cancel themselves out and the resolution mostly depends on the measurement system’s sensitivity. In this paper we give an overview of the different parameters influencing the successful implementation of optical nondestructive testing (ONdT) methods. In a second step, we compare shearography and deflectometry, identify relevant parameters and show restrictions of both methods with regard to the systems used. We present measurements with different methods and show how these results can be compared. We discuss the feasibility of both methods and the applicability of the systems used in a production line with respect to parameters concerning the quality control of produced goods.

Phase measuring deflectometry is an emerging technique to measure specular complex surface, such as aspherical surface and free-form surface. It is very attractive for its wide dynamic range of vertical scale and application range. Because it is a gradient based surface profilometry, we have to integrate the measured data to get surface shape. It can be cause of low accuracy. On the other hand, interferometry is accurate and well-known method for precision shape measurement. In interferometry, the original measured data is phase of interference signal, which directly shows the surface shape of the target. However interferometry is too precise to measure aspherical surface, free-form surface and usual surface in common industry. To assure the accuracy in ultra-precision measurement, reliability is the most important thing. Reliability can be kept by cross-checking. Then I will propose measuring method using both interferometer and deflectometry for reliable shape measurement. In this concept, global shape is measured using deflectometry and local shape around flat area is measured using interferometry. The result of deflectometry is global and precise. But it include ambiguity due to slope integration. In interferometry, only a small area can be measured, which is almost parallel to the reference surface. But it is accurate and reliable. To combine both results, it should be global, precise and reliable measurement. I will present the concept of combination of interferometry and deflectometry and some preliminary experimental results.

Until recently, the problem of reconstructing specular surface shapes from deflectometric registration data was considered inherently ambiguous, and thus requiring additional information in order to uniquely determine the absolute surface position. In 2013, Liu, Hartley and Salzmann suggested a solution to the reconstruction problem which employed the first-order derivatives of the registration data in order to recover the absolute depth of the surface along each camera ray. In this work, we demonstrate an alternative derivation of equivalent results, leading to more computationally efficient and tractable expressions. Re-formulated in terms of normal vector field, our results provide a natural regularization that together with or without external regularization data could be easily used within the existing reconstruction algorithms. We further elaborate on the stability and the uniqueness of the solution. In particular, we find conditions when a shape cannot be uniquely recovered and identify two equations that characterize the families of such shapes.

Phase-measuring deflectometry is a powerful method to measure reflective surfaces. It is relatively easy to extract slope and curvature information from the measured phase maps; however, retrieving shape information depends very sensitively on the calibration of the camera and the geometry of the measurement system. Whereas we have previously demonstrated shape uncertainties below 1 μm, the range below 100 nm is currently inaccessible to deflectometric shape measurement. On the other hand, the astounding sensitivity of deflectometry can be put to good use for deformation measurements. The evaluation of corresponding shape differences rather than absolute shapes is much less susceptible to system calibration errors and its resolution is given mostly by the measurement system’s sensitivity. We give an overview of recent progress in difference deflectometry. Firstly we show results from solar mirror substrates under load to detect flaws with high sensitivity. Secondly we present a preliminary simulation study of achievable deformation-measurement uncertainties to assess the feasibility of deflectometric characterisation of actuator performance and gravity sag for the mirror segments of the European Extremely Large Telescope (E-ELT). Results for the relevant Zernike terms show reliable detection of Zernike coefficients at the 25 nm level. Random artefacts related to noise in the phase measurements are seen to translate into bogus Zernike terms, and we discuss possible mitigation techniques to enhance the sensitivity and accuracy further.

Mid-spatial frequency structure on an optical surface induces small-angle scatter in the transmitted wavefront. Freeform surfaces are particularly susceptible to mid-spatial frequency errors due to the sub-aperture nature of the fabrication processes. Several surface metrology methods that work for freeform surfaces use an indirect principle, reconstructing the surface shape from measured surface slope data. The integration process in the presence of measurement noise adds a spatial correlation to the dataset, leading to spurious spatial frequency structure. In this paper, we use the autocorrelation function to characterize and evaluate this artificial mid-spatial frequency structure on optical surfaces that are reconstructed by zonal integration methods.

There are several sources of error in interferometry to consider when testing surfaces in a non-null configuration. A model of the interferometer is typically used to calibrate these errors, but the model differs from the actual interferometer due to the alignment and tolerance of individual components. Reverse raytrace calibration using a model that differs from the real system corrects some errors but introduces others. Reverse optimization using measurements from known test configurations or configuration changes can produce a model that better reflects the real system. This paper addresses the tolerances required to obtain calibration precision from reverse ray tracing. The sources of error can be separated in a way that allows the amount of correction to be compared to the generated errors from misalignment. These errors can be expressed in a generic way that can be applied to any arbitrary interferometer architecture or test surface shape. The simulation results of a standard interferometer with standard tolerances shows that errors corrected by reverse ray tracing can be on the same order as the errors generated by reverse ray tracing an incorrect model. The efficacy of the calibration method resides in correction of other errors such as distortion and ray intercept coordinate error. These corrections are much larger than misalignment errors for surfaces with large departures. This method can be used to determine the level of interferometer component alignment required to accurately measure large departure surfaces with reverse ray tracing.

Fizeau interferometer is widely used to test the surface deformation of the optical lens surface profile. However, in some measurement circumstances the common path condition of the Fizeau configuration does not hold. For example, the subaperture scanning interferometry of asphere or the non-null aspherical element testing has dense fringe spacing. Systematic aberrations of non-null testing are introduced into the measurement wavefront with the high wavefront slope of the returning beam. We propose to use a two-dimension scanning device to drive a test ball to different fields of the Fizeau interferometer for the the interference phase at each field. By least square fitting the measurement, we can get the double Zernike polynomial coefficients representing the field dependent aberrations in the interferometer system. According to the coefficients, the off-axis aberrations in the interferometer can be identified

The paper proposed a large field of view (FOV) measurement with calibrating the camera and measuring simultaneously. In the measurement, the whole FOV was divided into several smaller ones with overlapping areas between each other. The overlapping areas should contain at least 4 noncollinear feature points in each for computing external parameters and at least 4 noncollinear control points in one of them to start the calculation. To obtain the measurement of the whole large FOV, 2 images (or more) of each small fields of view needed to be taken from different angles. In the process of calculation, theoretical values of the camera were used as the initial values of the internal parameters and the initial values of external values were obtained from a new solution for P4P problem. So, the internal parameters of the camera, the external parameters for each image, and the 3D coordinates of the feature points in the large field of view could be acquired by adjustment method. In our experiment, the large field of view range was 500mm×500mm, the smaller ones corresponding to each image was 200mm×200mm, and the ultimate measurement accuracy was 12μm.

Single-frame fringe pattern processing and analysis is an important task of optical interferometry, structural illumination and moiré techniques. In this contribution we present several algorithmic solutions based on the notion of Hilbert-Huang transform consisting of empirical mode decomposition algorithm and Hilbert spectral analysis. EMD adaptively dissects a meaningful number of intrinsic mode functions from the analyzed pattern. Appropriately managing this set of functions results in a powerful fringe processing tool. We describe in detail especially tailored manners proposed to extend the EMD algorithm to 2D and perform Hilbert-transform-aided efficient fringe pattern denoising, detrending and amplitude/phase demodulation.

A post-processing technique based on principal components analysis (PCA) is proposed for shearography for defect detection. PCA allows decomposing a time series of images into a set of images called Empirical Orthogonal Functions (EOF), each showing features with a given variability in the time series. We have applied PCA on composite samples containing various defects at different depths and which undergo transient thermal wave. Analyzing the temporal series shows the shallow defects appearing first whereas the deeper ones appear later. With PCA all the defects appear in one or two of the EOF, easing the identification of defects.

A windowed, optimal and tracking (WOT) strategy for measurement data analysis is described, explained and discussed. Many fringe pattern analysis and digital image correlation algorithms adopted this strategy, and thus their similarities and links are revealed. Although this strategy is not new, highlighting it is believed to be helpful for future algorithm development.

A review of our recently developed fringe pattern processing techniques utilizing two dimensional continuous wavelet transform is presented. Their development significantly broadens the range of 2D CWT capabilities. Namely they enable analysis of images containing multiple fringe sets and the carrier fringe contrast reversal. The methods are fully automatic and require no user interference. Their validity and robustness are confirmed using simulations. Furthermore, a novel Talbot interferometer setup utilizing binary amplitude checker gratings with its output fringe patterns successfully analyzed utilizing 2D CWT technique is presented.

Phase retrieval is a basic step for most interferometric techniques. Both spatial and temporal approaches are frequently used. Temporal methods require a sequence of images with very well know phase shifting increments to produce accurate results. Sometimes environmental disturbances can add random phase values that can result in a sequence of images with virtually unknown phase shift increments. This paper presents and evaluates an approach to retrieve phase values from a sequence of five or more phase shifted images by unknown quantities. The phase shifting increments are determined from Lissajous ellipsis. This paper introduces the use of N-dimensional Lissajous figures to determine phase shifting increments. The use of additional dimensions makes the phase shifting increment determination more robust and less dependent of the pixel choices. The mathematical background is detailed and discussed. The paper presents and evaluates simulations and real world examples using fringe projection and speckle interferometry.

The large number of projections needed for tomographic reconstruction makes prohibitive the use of algebraic methods for fast phase object reconstruction. However, for smooth and continuous phase objects, the reconstruction can be performed with few projections by using an algorithm that approximates the phase as a linear combination of gaussian basis functions. This work presents an accurate algebraic reconstruction of a flame temperature from two independent interferometers using a He-Ne laser (623.8nm).

For the surface shape measurement of a semiconductor with a highly reflective index, it is important to effectively suppress the harmonic signals from multiple reflections. In application, the phase extraction algorithm should have a maximum value when there is no phase-shift miscalibration. In this presentation, a new 4N - 3 phase extraction algorithm, which has the ability to suppress harmonic signals and exhibits a fringe contrast maximum value when there is no phaseshift error, was derived. This new 4N - 3 algorithm consists of a new polynomial window function and a discrete Fourier transform term and has the ability to compensate for 2^nd-order nonlinearity in the phase shift. The suppression ability of the new polynomial window function is compared with other conventional window functions. The sampling functions of the new 4N - 3 algorithm have much smaller amplitudes in the vicinity of the detection frequency than does synchronous detection or other phase extraction algorithms with conventional window functions.

An algorithm for phase unwrapping based on swarm intelligence is proposed. The novel approach is based on the emergent behavior of swarms. This behavior is the result of the interactions between independent agents following a simple set of rules and is regarded as fast, flexible and robust. The rules here were designed with two purposes. Firstly, the collective behavior must result in a reliable map of the unwrapped phase. The unwrapping reliability was evaluated by each agent during run-time, based on the quality of the neighboring pixels. In addition, the rule set must result in a behavior that focuses on wrapped regions. Stigmergy and communication rules were implemented in order to enable each agent to seek less worked areas of the image. The agents were modeled as Finite-State Machines. Based on the availability of unwrappable pixels, each agent assumed a different state in order to better adapt itself to the surroundings. The implemented rule set was able to fulfill the requirements on reliability and focused unwrapping. The unwrapped phase map was comparable to those from established methods as the agents were able to reliably evaluate each pixel quality. Also, the unwrapping behavior, being observed in real time, was able to focus on workable areas as the agents communicated in order to find less traveled regions. The results were very positive for such a new approach to the phase unwrapping problem. Finally, the authors see great potential for future developments concerning the flexibility, robustness and processing times of the swarm-based algorithm.

Optical 3D profilers based on Coherence Scanning Interferometry (CSI) provide high-resolution non-contact metrology for a broad range of applications. Capture of true color information together with 3D topography enables the detection of defects, blemishes or discolorations that are not as easily identified in topography data alone. Uses for true color 3D imaging include image segmentation, detection of dissimilar materials and edge enhancement. This paper discusses the pros and cons of color capture using standard color detectors and presents an alternative solution that does not rely on color filters at the camera, thus preserving the high lateral and vertical resolution of CSI instruments.

We present a dual-wavelength diffraction phase microscopy (DW-DPM) that obtains the wavelength-differentiated dual phase images in a single shot of interference fringe acquisition. For this, the diffraction phase microscopy (DPM) system was constructed with a transmission grating and a spatial filter that form a common-path interferometer. With a light source of two spectral components, a different diffraction order of the grating was utilized for each. This resulted in a combined but distinguishable interference pattern to be acquired by a single image sensor. In this research, our dualwavelength phase imaging scheme was applied to simultaneously measure dispersion of a sample. Stable and reliable measurements could be performed in a single shot due to the robust structure of our DW-DPM system.

In this work the stagnation problem in iterative single beam multiple intensity reconstruction algorithms is reduced by combining deterministic and iterative phase retrieval techniques in order to compensate for paraxial artifacts. This combined technique has a better convergence, because it suppresses better the stagnation problem present in iterative phase retrieval techniques. The reported hybrid deterministic-iterative phase retrieval techniques can be successfully employed for cases where an iterative solver is trapped in a local minimum, and moreover, allows increasing the convergence of iterative solvers.

Classical time-averaging and stroboscopic interferometry are widely used for MEMS/MOEMS dynamic behavior investigations. Unfortunately both methods require an amplitude magnitude of at least 0.19λ to be able to detect resonant frequency of the object. Moreover the precision of measurement is limited. That puts strong constrains on the type of element to be tested. In this paper the comparison of two methods of microobject vibration measurements that overcome aforementioned problems are presented. Both methods maintain high speed measurement time and extend the range of amplitudes to be measured (below 0.19λ), moreover can be easily applied to MEMS/MOEMS dynamic parameters measurements.

The laser damage threshold of KDP crystals is one major limitation in many high-power laser systems. Investigation of laser damage behavior of KDP crystals shows that the major reason for laser damage is the growth defects in the bulk of the materials. Therefore, an effective diagnostic method for those defects is quite necessary for producing KDP crystals with high enough damage threshold to meet the requirement of high power laser applications. In this paper, we reported the characterization of bulk defects in KDP crystals using a three dimensional photothermal microscope based on a laserinduced photothermal lensing technique. Several 3D mapping of the bulk defects were obtained. The results indicated that both surface defects and bulk defects can be determined and analyzed using the 3-D photothermal microscope. The details of the development of the 3-D photothermal microscope were also presented. The system provided user-friendly operations of the defects characterization process and showed great potential of application for characterization of low absorption optical materials.

Advanced Virgo is an upgrade to the Virgo detector located near Pisa, Italy designed with an ultimate goal of the detection of gravitational waves originating from cosmic sources. The upgrade will provide an order of magnitude increase in the sensitivity of the detector and allow the exploration of a volume 1,000 times larger than Virgo. The system design includes 21 ‘half meter’ class optics for which Zygo has been selected as the primary supplier. The optic components have nanometer level low-order figure requirements along with sub-angstrom roughness requirements specified over a wide spatial frequency band. In this paper the results and methodologies used in achieving such extreme requirements that are typically associated with the semiconductor lithography industry will be presented.

Distributed Fiber optical sensor has been widely used in communication cables and pipelines defense. Among them, Fiber Sagnac Interferometer shows several merits such as low noise, low requirement and high reliability. While the loop-based configurations are difficult in practical application for two aspects: the inconvenience to install Sagnac loop along a line (such as communication cables) and the isolation of the unused half of the Sagnac loop. Though some linear structures with delay loops or dual-loop were developed to satisfy reality requirements, they usually make a sacrifice of sensitivity and have complex circuits. To acquire high sensitivity with simple circuits, we propose a structure in which the two sides of Sagnac loop are in one cable. When a disturbance applies to the cable, one fiber is compressed and another is stretched, and vice versa. The phases of clockwise (CW) light and the counter clockwise (CCW) light are affected by the disturbance at the same time but with different direction. It means that the phase affection acting on the two fibers by the intrusion are synchronous but differ with half period. Besides the advantages of linear laying and high sensitivity, the high order of null frequencies are integer multiple of the fundamental null frequency. Closer null frequencies make more accuracy on peaks location on the Fourier transform. Experiments on simulating the intrusion in lab have been launched. A 50m resolution has been achieved when the intrusion distance is 100km. This structure is proved simple and accurate.

This paper presents a miniaturized fringe projection system that only uses two fibers to potentially achieve superfast (e.g., MHz to GHz) 3D shape measurement speeds. The proposed method uses two optical fibers that carry the same wavelength of laser light with polarization and phase information properly modulated to generate high-quality sinusoidal fringe patterns through interference. The high-speed phase shifting is achieved by employing a high-speed Lithium Niobate (LN) electrooptic phase modulator. Since only two optical fibers are used to generate sinusoidal patterns, the system has a great potential of miniaturization for applications where the sensor size is critical (e.g., 3D endoscopy). Principle of the proposed techniques will be introduced, and preliminary experimental results will be presented in this paper to prove the success of the proposed method.

This paper introduces a novel polarization structured light pattern projector was done by taking into account the unique characteristic of the pixelated camera and a spatial light modulator (SLM) used. Height variations of reflective samples are retrieved by using fringe contrast modulation on an uniaxial configuration. By placing a special retardance pattern on the SLM, the pixelated camera will detect a phase shifted sinusoidal pattern where later its contrast change will be used to retrieve the height information of the sample under study. The presented system takes into account the defocus change obtained by the height variation of the sample by encoding the information on the fringe contrast of the projected structured light pattern by the SLM. The final purpose of this work is to present a single shot 3D profilometry system based in fringe contrast analysis. Experimental results of a moving glass slide are presented.

This work is focused on a description and an analysis of an optimization method for the evaluation of small deviations of optical surface shape in interferometric testing. The proposed method does not require a detailed analysis of the interference field as it is necessary with classical evaluation methods of interference patterns and it uses the optimization techniques for the determination of the deviation of the tested surface from its nominal shape. This method compares interferograms, which correspond to the nominal shape of optical surfaces, and interferograms of the tested optical surfaces using the suitable merit function based on variance of two interference patterns. It can be used for the comparison of two surface shapes.

Phase unwrapping is an intermediate step for interferogram analysis. A smooth phase associated with an interferogram can be estimated using a curve mesh of functions. Each of these functions can be approximated by a linear combination of basis functions. In some cases constraints are needed to solve the phase unwrapping problem, for example, when estimated values never can be negative. In this work it is proposed a method for phase unwrapping using a set of functions in a mesh which are lineal combinations of Chebyshev polynomials. Results show good performance when applied to noisy and noiseless synthetic images.

A fiber-optic laser Doppler velocimeter (LDV) combining non-mechanical scanning and multipoint measurement is proposed for two-dimensional velocity distribution measurement on a cross-sectional plane. The LDV consists of a main body including a tunable laser and LiNbO3 phase-shifter array, and a probe including diffraction gratings. The phaseshifter array is used to generate spatially encoded measurement points aligned in the transverse direction by multichannel optical serrodyne modulation, and these points are axially scanned with wavelength change. Two-dimensional velocitydistribution measurement is demonstrated using a probe setup with an 8-channel beam array.

Requirements for the measurement resolution in the sub-nanometer range have become quite common which includes not only the repeatability or reproducibility but also the absolute measurement accuracy. The freeform lens for wavefront compensating contains some medium spatial frequency terms. The wavefront error of lithographic object lens is very small. One method to reduce the wavefront error of lithographic object lens is to use the freeform lens. The freeform lens for compensation needs more accuracy than the object lens. We can also use freeform lens of sphere or aspheric for compensation. The testing accuracy of sphere and aspheric lens are hard to achieve 1nm. The sphere and aspheric will contain the power term and are hard to find the cat-eye. The ion beam figure system (IBF) is the best polishing machine for nanometer manufacture which will polish the PV of 2um for several weeks even months. Usually we use the PV 200nm lens for compensation. So the freeform for compensation looks like a flat. In this paper we will show the testing experiment of the freeform and the testing problem. The freeform surface is created by 66 Zernike polynomials which are based on the flat lens. The freeform flat is polished by the ion figuring machine of NTG. The environment such as temperature, vibration, humidity is controlled well. The Zygo's interferometer Verifire Ashpere with absolute testing method is used to test the freeform. Position Accuracy is a problem in optical testing and manufacture. The high accuracy testing can’t be determined by one method, we need the different method to compare the result especially these method will contain some defects. The defects of the recently absolute testing method are discussed.

In the present paper low frequency moiré fringe patterns are used as secure numerical code generator. These moiré patterns are experimentally obtained by the superposition of two sinusoidal gratings with slightly different pitches. The Bi₁₂TiO₂₀ photorefractive crystal sample is used as holographic medium An optical numerical base was defined with patterns representing 0,1 and -1 digits like bits. Then, the complete set of these optical bits are combined to form bytes, where a numerical sequence is represented. The results show that the proposed numerical code could be used as standard numerical identification in robotic vision or in transmition of security numerical keys.

The use of zinc oxide (ZnO) for its application as gas sensor is frequent in the industry. One important element for the characterization of this kind of structure is the measurement of the material thickness deposited on a substrate. In this work, an optical method for determining the measure of the ZnO material thickness, in this case a point diffraction interferometer (PDI) is used. The PDI uses few optical elements in the arrangement and its low cost represents an easy implementation. Also, the ZnO sample does not require any chemical treatment to be measure; consequently it does not need an extra step in the measurement process. The purpose of this arrangement is to implement it as a measuring tool for the laboratory of sensor films of the Autonomous University of the State of Hidalgo. For early results, it is proposed to measure the thickness of a ZnO film larger than one micron of the ZnO film, and the results are compared with the traditional method using a talkstep.

Gelatin thin films inserted in a Mach – Zehnder interferometer were used to monitor Relative Humidity (RH). When RH varied, gelatin film thickness and refractive index also changed. As a result interference pattern moved horizontally. A fixed detector, with a pinhole in front of it, was placed at the interference pattern. It sampled the pattern when it moved. These intensity values were used to find a calibration plot relating intensity as a function of RH.

We review the interferometric double-imaging area (IDIA) technique,¹ a new holographic principle and an optical setup for doubling the field of view of interferometric imaging setups, and obtaining wider off-axis interference areas with low-coherence light sources. The method enables measuring larger samples that cannot fit into one interferometric field of view without decreasing the microscope magnification or performing scanning, while losing in the camera frame rate. The new principle was implemented using a modified off-axis τ interferometer, which is compact, portable, and easy to construct and align even with low-coherence light sources. We demonstrate using the proposed technique for imaging the quantitative phase maps of a transparent microscopic test target and live neurons.

Periodic error is a main error source that limits the measurement accuracy in heterodyne laser interferometry. An external cavity diode laser (ECDL) based Fabry-Perot (F-P) interferometer referenced to an optical frequency comb (OFC) is proposed to characterize the periodic error in heterodyne interferometers. The Pound-Drever-Hall locking technique is employed to lock the tracking ECDL frequency to the resonance of a high finesse F-P cavity. The frequency of a reference ECDL is locked to a selected mode of an OFC to generate a stable single optical frequency. The frequency change of the tracking ECDL induced by the cavity displacement is measured by beating with the reference ECDL locked to the OFC. Experiments show that the F-P interferometer system has a displacement resolution of 1.96 pm. We compared the measurement results of our system with a commercial plane mirror heterodyne interferometer. The period if the periodic error is about half wavelength, with an error amplitude of 4.8 nm.

Proximity exposure techniques in lithography are getting more and more popular because of the cost of ownership advantage of mask aligners compared to projection systems. In this paper a gap between simulation and the final result, the prints will be closed. We compare high resolution measurements of intensity field behind amplitude masks with proximity correction structures with simulations gain insight in limitation of proximity lithography. The final goal is to develop techniques that allow enhancing the resolution by using advanced optical correction structures. The correction structures are designed with Layout Lab (GenISys GmbH), prints are done and characterized and the results are compared with measured light intensity distributions. The light intensity distributions behind the mask are recorded using a High Resolution Interference Microscopy (HRIM). We concentrate on an example study of edge slope improvement and we explore possibilities of improved parameters like edge slope at different proximity distances. Simulations and measurements are compared and discussed.