The measurement accuracy of an interferometric optical test is generally limited by the environment. This paper discusses two single-shot interferometric techniques for reducing the sensitivity of an optical test to vibration; simultaneous phase-shifting interferometry and a special form of spatial carrier interferometry utilizing a micropolarizer phase-shifting array. In both techniques averaging can be used to reduce the effects of turbulence and the normal double frequency errors generally associated with phase-shifting interferometry.

Most full-field heterodyne interferometry systems are based on complex electro-mechanical scanning devices. In this study, however, we present an alternative non-scanning approach based on a low frequency heterodyne interferometer employing standard CCD and CMOS cameras. Two frequency locked acousto-optical devices were used to obtain two laser beams with an optical frequency difference as low as 3 Hz. The interference of those beams generated a suitably low frequency carrier signal that allowed the use of a common 25 frame/second CCD camera. Using a digital CMOS camera and acquiring a limited number of randomly accessible pixels, measurements with much higher carrier frequencies were also possible. The advantages of the heterodyne technique with respect to common phase-stepping methods are the shorter response time and lower sensitivity to sources of uncertainty such as drift, vibrations and random electronic noises. In order to directly compare the heterodyne and phase-stepping techniques experimentally, the same interferometer was used for both methods. The switching between operation modes was achieved by simply altering the electronic driving signals of the acousto-optical devices where for the phase-stepping mode, the frequency difference of the driving signals was set to zero. The phase steps were obtained by a piezo-driven mirror. Comparing the phase difference between two pixels in an image, approximately 0.01 radian of standard deviation, corresponding to a resolution of λ/628, was achieved by heterodyne technique, as compared to 0.06 radian by the phase-stepping method. The interferometer with the CMOS camera was applied to monitor the refractive index variation across a micro-channel where two liquid flows were mixed. Also, the capability for fast, time-resolved full-field optical refractive index measurements was demonstrated. The examples presented show how the high sensitivity of the heterodyne technique allows the study of a number of sources of uncertainty that were not otherwise easily quantifiable using standard full field methods.

In this paper, we propose a novel three-dimensional phase unwrapping algorithm that extends the “two-dimensional phase unwrapping algorithm based on sorting by reliability following a non-continuous path” into three dimensions. The proposed algorithm depends on a quality map to unwrap the more reliable voxels first and the less reliable ones last. It follows a non-continuous path to perform the unwrapping process. Computer simulation has demonstrated that the proposed algorithm is more suitable than its two dimensional counterpart when used to unwrap volumetric data.

We present a novel detection scheme for coherent anti-Stokes Raman scattering (CARS) which is capable of substantially suppressing coherent background signals which are a basic problem associated with CARS. It exploits the fixed phase relationship between pump, Stokes and CARS fields together with the strong phase coherence in supercontinua generated by femtosecond pulses. Three phase-locked noncollinearly phase-matched optical parametric amplifiers (NOPAs) seeded by a common white-light continuum are used for the realization of a heterodyne signal detection. In combination with proper pulse timing, i.e. appropriately time-delayed probing and heterodyning, a gating mechanism is provided to significantly suppress resonant and nonresonant solvent background signals. Therefore the demonstrated technique is suitable for high-contrast vibrational imaging.

The correlation structure of 2-D Stokes vector parameters of physiologically normal and pathologicaly changed biotissues is investigated. The totality of diagnostically urgent interconnections between biotissue physiological state and statistical moments of 2-D Stokes vector parameters is found.

In-line holography is a simple approach for high resolution imaging. It has been extensively investigated due to it can effectively utilize the space-bandwidth of the digital recording instrument, such as CCD or CMOS. However, since the fact that the reference wave and the object wave are overlapped during the hologram was recorded, the reconstructed image is blurred by the ghost image. This shortcoming limits the applications of the in-line holography. Therefore, an effective reconstruction algorithm is important for generalizing the application of the in-line holography. In this presentation, some approaches based on the iterative phase retrieval algorithms are reported for in-line holograms reconstruction. Firstly, the YG algorithm and the GS algorithm are used to reconstruct pure absorption object from their in-line holograms, respectively. The differences between these two algorithms on in-line hologram reconstruction are analyzed. Then the GS algorithm is extended to reconstruct whole optical field form double or multiple holograms. At last, a new approach for reconstructing object from a hologram series is presented. Experimental results show that all these methods can reconstruct original object well.

A two stage method for allowing direct perfect superimposition and comparison of Fresnel-transform reconstructions of digital holograms recorded at different wavelengths is proposed and demonstrated. The method allows to adjust the size of the reconstruction pixel by varying the reconstruction distance of the first stage. Demonstration is given by superimposing in focus numerical reconstructions of holograms recorded at different wavelengths. The method can be potentially very useful for real-time monitoring in biological processes.

The aim of this work was to study the possibility of improving the resolution of digital holography. To achieve this goal we recorded digital holograms of microlines of width in the micrometer region in a lensless Fourier-transform setup. In such a way spatial frequency of the hologram can be reduced in high numerical aperture geometry. A He-Ne laser was used in the experiments. Holographic images of the test objects were reconstructed using two methods. The first one is based on fast Fourier-transform algorithm. The second one uses Monte-Carlo method. In our paper we present a comparative analysis of the reconstructed holographic images using these methods. The effects of limited resolution and nonlinearity of the CCD on the reconstructed image were included in the numerical reconstruction by multiplying the integrand of the Fresnel-Kirchhoff integral by the product of two functions, describing of the above characteristic of the CCD. This method can serve as a basis for resolution enhancement in DH via de-convolution.

Speckle fringe patterns of ESPI are full of high-spatial-frequency and high contrast speckle noise which defies normal process methods. Filtering with contoured windows has been proven to be an efficient approach to filter off the speckle noise while reserving the fringe patterns obtained by subtraction of two original speckle patterns. Furthermore, with contoured windows, the contoured correlation fringe pattern (CCFP) method proposed by the authors can derive highquality fringe patterns of ESPI with speckle-free, smooth, normalized and consistent fringes from two original speckle patterns. CCFP method can also extract the phase field with a single-step phase-shifting. Determination of contoured windows is a key step in CCFP method. The contoured windows used to be determined by fringe orientations only and this process would generate accumulated errors. In this paper, two new algorithms to determine the contoured windows according to the fringe intensity slope and the distance ratio to neighboring skeletons with the help of the local fringe direction are proposed. These new techniques can determine contoured windows more precisely and more robustly with no accumulated errors. Some applications of our new contoured windows are also presented.

In this paper, we will derive a phenomenological model of the bidirectional reflectance distribution function of non-Lambertian metallic materials typically used in industrial inspection. We will show, how the model can be fitted to measured reflectance values and how the fitted model can be used to determine a suitable illumination position. Together with a given sensor pose, this illumination position can be used to calculate the necessary shutter time, aperture, focus setting and expected gray value to successfully perform a given visual inspection task. The paper concludes with several example inspection tasks.

We present a new method to segment images of structured surfaces from illumination series, i.e. sets of images of an object recorded with different lighting settings. We use a parallel light source whose angle of incidence is described by the azimuth and the elevation angle. Depending on the surface topography, characteristic patterns are described by the intensities viewed by the camera depending on the illumination direction. The segmentation itself is based on cluster analysis in a multi-dimensional feature space. The resulting classes correspond with the identified segments of the surface image. A crucial step within this approach is the definition of meaningful features. We focus on features that can be extracted from the signal described by the intensities at a single surface location depending on the illumination direction. We investigate features based on moments of this intensity signal as well as on its frequency decomposition with respect to the illumination direction. Furthermore, we show that features of this kind can be used to robustly segment a wide variety of textures on structured surfaces. In any case, since no spatial neighbourhood is utilized to compute the features, i.e. "averaging" takes place only in illumination domain, no spatial resolution must be sacrificed. Consequently, even very small regions can reliably be segmented, as is necessary when defects are to be detected.

In the paper a new method for scaling of phase values into (x,y,z) co-ordinates supporting methods with absolute phase determination e.g. fringe projection / Gray code techniques is presented. It is based on calculation of characteristic polynomials describing relationships between phase values and real (x,y,z) co-ordinates in measurement volume. Coefficients of these polynomials are calculated on the base of phase distribution on known 2D-calibration model positioned manually in several unknown positions inside measurement volume. It introduces new way of calibration by two step process. First, it calculates exact positions of model on the base of its phase distributions and secondly it evaluates coefficient of polynomials. Applicability of the method described is proven by calibration of 3D shape measurement system based on unknown, commercially available projection and detection systems with unknown parameters of imaging optics and geometrical set-up. Exemplary measurement result of freeform object is presented.

A new self calibrating optical 3D measurement system using fringe projection technique named “kolibri 1500” is presented. It can be utilised to acquire the all around shape of large objects. The basic measuring principle is the phasogrammetric approach introduced by the authors /1, 2/. The “kolibri 1500” consists of a stationary system with a translation unit for handling of objects. Automatic whole body measurement is achieved by using sensor head rotation and changeable object position, which can be done completely computer controlled. Multi-view measurement is realised by using the concept of virtual reference points. In this way no matching procedures or markers are necessary for the registration of the different images. This makes the system very flexible to realise different measurement tasks. Furthermore, due to self calibrating principle mechanical alterations are compensated. Typical parameters of the system are: the measurement volume extends from 400 mm up to 1500 mm max. length, the measurement time is between 2 min for 12 images up to 20 min for 36 images and the measurement accuracy is below 50μm.The flexibility makes the measurement system useful for a wide range of applications such as quality control, rapid prototyping, design and CAD/CAM which will be shown in the paper.

Increasing demands for the monitoring of tolerances of small mechanical and optical precision components require improved measurement techniques. In this paper the basic concept and different optical designs of a confocal microoptical distance-sensor are presented. The sensors use the chromatic-confocal measurement principle which does not require a mechanical depth scan. Therefore, a chromatic-confocal point sensor can be designed without any moving parts. This fact is used to design a miniaturized sensor head with an outer diameter smaller than two millimetres. A special feature of the sensor head is its capability to measure sideways. This enables e.g. to measure surfaces in small drilling holes.

In this paper, the realization and characterization of a microoptical sensor using the chromatic confocal principle is presented. The sensor head is designed for distance gauging applications in high aspect ratio cavities with a diameter of about 2 mm. The first part of this paper focuses on the design and fabrication process of the hybrid optical benches, which combines refractive and diffractive micro optical components. Very tight tolerances of the optical path are required for the functionality of the sensor. Therefore the alignment structures and mounts between the different optical elements are produced from PMMA using deep X-ray lithography, the first step of the LIGA process. In the second part of this paper the characterization of first prototypes using different light sources are described and results presented.

A new null ellipsometer has been recently proposed that uses photoelastic modulator (PEM). The phase modulation adds a good signal-to-noise ratio, high sensitivity, and linearity near null positions to the traditional high-precision nulling system. The ellipsometric angles Delta and psi are obtained by azimuth measurement of the analyzer and the polarizer--PEM system, for which the first and second harmonics of modulator frequency cross the zeros. In this paper we discuss influence of component imperfection on precision of null measurement. Particular interest is devoted to azimuth angle error of compensator and modulator. Effect of residual birefringence of PEM is discussed. We show that the null system is insensitive to ellipsometer misadjustment and component imperfections and modulator calibration is not needed.

A simple and compact electronic speckle pattern interferometry system using a reflection holographic optical element is presented. The reflection holographic optical element is recorded on an acrylamide based photopolymer formulated and prepared at the Centre for Industrial & Engineering Optics. Light intensity of 40mW/cm2 with an exposure time of 60 seconds was used in fabricating the holographic optical element. The vibration mode patterns of a 4 cm diameter thin circular sheet of brass metal attached to a 4 cm diameter paper cone loud speaker are presented.

Time-resolved observation of the fuel/air mixing process prior to ignition is crucial for the development of modern internal combustion engine concepts. The presented fiber optic sensor is designed for the acquisition of in-cylinder data in the area close to the ignition spark, based on UV-laser-induced fluorescence of organic fuel compounds. Excitation and fluorescence light are separately guided through silica fibers. The detection volume is defined by the optical design of the sensor head. Since the related components are completely integrated into a modified spark plug, the sensor can be applied to unmodified production line engines. We present the fundamental spectroscopic concept, the solution for the minimal invasive access through the spark plug and tracer spectra measured with a prototype.

This paper reports measurement results and some design details of railway measurement systems based on optical principles. The quality of railway lines is crucial for reliability and safety and therefore to be controlled regularly. Special measuring vehicles operate permanently on all railway lines, even during regular traffic situations. Therefore the measurement systems used to record the data have to be fast enough even at high speeds and robust enough to provide reliable data under almost any environmental conditions. The application of optical methods is advantageous concerning accuracy and speed but of course limited by external influences. We report here measures enabling even a sensitive optical measurement principle, the phase measurement technique, to be applied under these harsh environmental conditions. Exemplarily the optical and mechanical design of a clearance profile scanner is described. It is shown how to make the sensor insensitive against environmental conditions like contamination by dust or water or temperature changes. Measurement results of this scanner and of another system to measure the position of the contact wire are presented.

Future space missions, among which the Darwin Space Interferometer, will consist of several free flying satellites. A complex metrology system is required to have all the components fly accurately in formation and have it operate as a single instrument. Our work focuses on a possible implementation of the sub-system that measures the absolute distance between two satellites with high accuracy. For Darwin the required accuracy is on the order of 70 micrometer over a distance of 250 meter. We are exploring a technique called frequency sweeping interferometry, which involves interferometrically measuring a phase difference while sweeping the wavelength of a tunable laser. This phase difference is directly proportional to the absolute distance. A very high finesse Fabry-Perot cavity is used as a reference standard, to which the laser is locked end-points of the sweep. We will discuss the control system that drives the setup and show some first experimental results.

A non-contacting online caliper measurement has been papermakers' dream for over two decades. Currently, paper thickness is measured using buttons contacting the paper web on both sides. In such a configuration, paper thickness is assumed to be the distance between the contacting surfaces and determined by a magnetic measurement principle. However, this arrangement of contacting measurement has several disadvantages including sheet marking, hole creation, dirt build-up on the contacting buttons, wearing of the contacting surfaces, and even sheet breaks. Moreover, the current trends in paper manufacturing, especially the increasing use of recycled raw materials are necessitating the development of a more reliable thickness measurement solution that is not affected by dirt and other material on paper or board sheet surfaces. So far, a non-destructive, on-line thickness measurement has not been successfully applied in paper production environment. Recently, Metso Automation has successfully piloted in several mills a caliper sensor that does not contact the sheet on both sides and is able to measure paper thickness with sub-micron accuracy. The new sensor is based on single sided laser triangulation. This paper presents the measurement set-up and discusses the challenges encountered. Measurement results obtained in mill trials with various paper grades are reviewed and compared to those made simultaneously with contacting, on-line sensors and off-line laboratory results of the same sheet. Factors affecting the measurement with conventional and optical thickness sensors are also discussed.

Optical sensors exhibit a number of properties that make them interesting for a variety of applications in measurement science. The main contribution of this work is the development and the experimental validation of a 2D optical range sensor used in a quality control application. While various solutions for distance measurement in 2D exist, the proposed sensor and its associated signal processing algorithms are able to greatly simplify the sensor calibration and its on-site adjustment. The sensor design is motivated by the specific needs of quality control measurements on large cylindrical structures. Experimental results indicate the accuracy of the sensor and its applicability to quality control measurements.

In this paper the problem of optical distance measurements is considered. The proposed measurement system is based on the FMCW (frequency modulated continuous wave) method. A measurement acquisition system is realized from which the real data are collected. This system represents a two target scenario. After deriving a simple signal model for multi-target scenarios two different distance estimation procedures are introduced, a Fourier-based and a subspace algorithm. The signal model is verified using both simulated and measured data. Distance measurements are performed for real and synthetic data to investigate the performance of the measurements. It is known that the significant difference between the two algorithms is the resolution capability. Therefore, we investigate the case of closely spaced targets. In addition we study the performance for well separated targets concerning bias and variance.

In this paper we present phase shifting Talbot interferometry for the measurement of surface topography of the gas turbine blades. Interferograms of the different steps are recorded and displayed on the computer monitor using digital techniques. Presence of the harmonic components in the phase map due to the Ronchi gratings are removed by using Fourier filtering. The variation of the surface height at the different points of the objects is obtained by generating the phase map. The results obtained by phase shifting Talbot interferometric techniques are in good agreements with that of the measured by the manually controlled co- ordinate measuring machine. The critical analysis of results alongwith error analysis is presented.

A previously reported interferometer without intermediate optics is used to perform measurements on an aspherical extreme ultraviolet lithography mirror substrate. Acousto-optic modulation based phase shifting is used together with a novel phase retrieval algorithm to retrieve the phase distribution from our interferograms. The phase distribution is then processed by a previously reported inverse propagation algorithm to give the shape of the mirror under test. Our results are compared with measurements performed with conventional Fizeau interferometry and the discrepancies are discussed with reference to systematic error sources inherent in the classical and novel interferometers.

The dark field microscopy method with alternating grazing incidence illumination (AGID), developed at the PTB, offers the possibility to measure structures with lateral dimensions below the classical resolution limit. Moreover, this method offers the advantage of better dimensional measurements of phase objects, since higher contrasts compared to conventional bright field microscopy are obtained. As an example, the AGID-method can be used for the determination of linewidths on photomasks or wafers. A newly developed prototype measuring system based on the alternating dark field illumination is be presented. This system uses two diode lasers with the wavelength 374 nm as lightsources. This new method is be compared with conventional bright field microscopy. The distribution of intensity of an image of a given structure depends on the illumination and the geometrical parameters as well on the optical parameters. In particular the dependence on the polarization and the angle of incidence of the illumination is discussed. For modeling of the intensity distribution in the image we are using two different rigorous diffraction theories. On the one hand we use the rigorous coupled wave analysis (RCWA) method for the calculation of the diffracted electric and magnetic fields and on the other hand the finite elements (FEM) method. These two models are used for determining the linewidth from measurement data of the new prototype system. It will be shown that the newly developed system is a suitable tool for optical linewidth measurements which represents a meaningful addition to existing optical linewidth measurement systems.

Shape detection on objects of large and huge dimensions has always represented a challenging task, mostly by the practical point of view due to the size of the related measurement equipment. When the tested object is a mirror the measurements is additionally complicated, since the classical techniques of structured light cannot be directly applied. The method proposed in this paper has been applied to measure the curvature of a deformable mirror of 1-meter diameter for a heliostat plant. The mirror shape is obtained studying the spatial variations of a grating projected on the sample and reflected by it on a screen. The measurement set-up employs a PC projector and a digital camera. The results of this curvature assessment are compared to those derived from a simulation obtained by an optical design programme.

A scanning system consisting of an angle sensor and coupled distance sensors is used for high-accuracy profile form measurements of optical surfaces. This system allows both scanning stage errors and systematic errors of the distance sensors to be estimated. Additionally, a high lateral resolution is achieved. The optical surface profile is reconstructed from the measurements made by the angle and distance sensors by application of least-squares. A test set-up is presented and the results of optical form measurements are shown.

The methodology of phase encoded reflection measurements has become a valuable tool for the industrial inspection of components with glossy surfaces. The measuring principle provides outstanding sensitivity for tiny variations of surface curvature so that sub-micron waviness and flaws are reliably detected. Quantitative curvature measurements can be obtained from a simple approach if the object is almost flat. 3D-objects with a high aspect ratio require more effort to determine both coordinates and normal direction of a surface point unambiguously. Stereoscopic solutions have been reported using more than one camera for a certain surface area. This paper will describe the combined double camera steady surface approach (DCSS) that is well suited for the implementation in industrial testing stations

Standard high-speed Fourier domain optical coherence tomography (FD-OCT) and a modified version of FD-OCT; a line-field FD-OCT (LF-FDOCT) are demonstrated. LF-FDOCT is using the principle of FD-OCT for its depth resolution and a one-dimensional imaging optics for its one-dimensional lateral resolution. A mechanical C-scan drived by a galvano scanner is introduced into the FD-FDOCT, which shows a cross sectional OCT image without any mechanical scanning. The improved version of FD-OCT visualizes the three-dimensional structure of a sample with only one-dimensional scanning. Both standard FD-OCT and LF-FDOCT are applied to dermatological applications and visualize the inner structure of an in vivo human fingerpad.

During the past decade, optical coherence tomography (OCT) has been vigorously developed into a powerful tool for biomedical diagnosis applications. Because this technology has the nature of extracting the internal features of an object, its applications can be extended to document security, biometrics identification, and industrial inspection. In addition, its high imaging resolution makes OCT an ideal tool for massive storage/retrieval of 3D data. In this paper, we propose the 2D parallel OCT system and its application for multiple-layer information retrieval. We will study the issues that exist exclusively in this type of application, such as interlayer phase/intensity modulation and the parasitic fringe patterns resulting from the surfaces of the information layer. The basic procedure of the proposed OCT system includes three steps: 1) extraction of cross-section raw images at each layer of an object; 2) removal of the interfering fringes by algorithm derived from multiple phase-shifted images; 3) elimination of interlayer modulations and parasitic patterns. Other issues that may degrade the retrieved images are also discussed. The simulation results and experimental tomography obtained from different testing samples are presented and discussed.

A new spectral-domain interferometric technique employing a simple experimental setup is used to measure the group birefringence of a uniaxial crystal of known thickness over the wavelength range of the visible spectrum. The experimental setup comprising a white-light source, a Michelson interferometer, a polarizer, a uniaxial crystal, an analyzer, and a low-resolution spectrometer is utilized to record a series of spectral interferograms for different optical path differences (OPDs) adjusted in the Michelson interferometer. The spectral interferograms include interference fringes resolved only in a narrow spectral range around the so-called equalization wavelength at which the overall group OPD between interfering beams is zero. We measure the equalization wavelength as a function of the OPD in the Michelson interferometer to obtain directly the wavelength dependence of the group birefringence of a calcite crystal. Using the calcite crystal of two different thicknesses, we confirm that the measured dispersion of the group birefringence agrees well with the theoretical one. The thicknesses of the calcite crystal are also determined precisely from the slopes of linear dependences of the measured OPDs on the theoretical group birefringences.

We describes a new scheme of dispersive white-light interferometer that is capable of measuring the thickness profile of thin-film layers, for which not only the top surface height profile but also the film thickness of the target surface should be measured at the same time. The interferometer is found useful particularly for in-situ inspection of micro-engineered surfaces such as liquid crystal displays, which requires for high-speed implementation of 3-D surface metrology.

Presented is a comprehensive characterisation of a complementary metal-oxide semiconductor (CMOS) and digital signal processor (DSP) camera, and its implementation as an imaging tool in full-field optical coherence tomography (OCT). The camera operates as a stand-alone imaging device, with the CMOS sensor, analogue-to-digital converter, DSP, digital input/output and random access memory all integrated into one device, autonomous machine vision being its intended application. The 1024x1024 pixels of the CMOS sensor function as a two-dimensional photodiode array, being randomly addressable in space and time and producing a continuous logarithmic voltage proportional to light intensity. Combined with its 120dB logarithmic response range and fast frame rates on small regions of interest, these characteristics allow the camera to be used as a fast full-field detector in carrier based optical metrology. Utilising the camera in an OCT setup, three-dimensional imaging of a typical industrial sample is demonstrated with lateral and axial resolutions of 14μm and 22μm, respectively. By electronically sampling a 64x30 pixel two-dimensional region of interest on the sensor at 235 frames per second as the sample was scanned in depth a volumetric measurement of 875μm x 410μm x 150μm was achieved without electromechanical lateral scanning. The approach presented here offers an inexpensive and versatile alternative to traditional OCT systems and provides the basis for a functional machine vision system suitable for industrial applications.

Interferometric testing of micro-optical components involves some challenges due to problems such as Fresnel diffraction artefacts, the non-common path interferometer configuration, coherent noise as well disturbing interferences, and uncertainties in distance measurements. Recently we have developed a versatile Mach-Zehnder / Twyman-Green hybride interferometer for micro-optics testing. The system combines the advantages of both interferometer types and allows full characterization of lens and surface figure errors as well as radius of curvature and focal length measurements. The interferometer system is explained and measurement results of micro-lenses are presented. Furthermore, this paper is concerned with the metrology challenges of interferometric testing on microscopic scales.

Digital holographic Microscopy (DHM) is an imaging modality reconstructing the wavefront in a numerical form, directly from a single digitalized hologram. It brings quantitative data derived simultaneously from the amplitude and phase of the complex reconstructed wavefront diffracted by the object and it is used to determine the refractive index and/or shape of the object with accuracy in the nanometer range along the optical axis. DHM comprises a microscope objective to adapt the sampling capacity of the camera to the information content of the hologram. This paper illustrates some of the possibilities offered by DHM for micro-optics quality control. Actual results obtained by DHM, yielding an axial precision up to 3.7 nm, will be compared with measurements performed with interferometers by SUSS MicroOptics SA and with the profiles measured with a mechanical scanning probe instrument (Alpha step 200 from Tencor Instrument). Two different micro-lenses arrays where tested: a quartz refractive lenses array (observed with transmission DHM) and a Silicon refractive lens array (observed with reflection DHM).

The novel precise three dimensional shape measurement method using SEM and moire topography has been proposed. The possibility for measurement of wave length order by this method has also been shown. In this paper, the method with high resolution power based on the new measurement method is proposed by employing the fringe scanning technology for the shadow moire. The optical system is constructed with SEM using backscattering electrons, the grating holder which can shift the position of the grating, and the grating of which the pitch is 120 micro meter. Measurement using a bearing ball as a sample showed that the high resolution measurement around one macro meter can be performed by introducing the fringe scanning method to the new measurement.

In the image of laser scanning confocal microscope, an edge of a weak phase object is sometimes enhanced as bright and/or dark line. This phenomenon is thought to be caused by the interference effect of diffractive light from the edge. The imaging characteristics of this type of microscope are regarded as a product of the optical sectioning characteristics (I-Z response) and the optical property of its imaging system. The I-Z curve decreases monotonically with depth (Z) which is determined by a diameter of pinhole and a numerical aperture (NA) of imaging system. Analyzing partially coherent imaging system under the weak phase approximation, we found that intensity image generated with increasing a defocus in observing weak phase only object of step-like figure. Accordingly the peak in optical transfer function (OTF) arose at some point of specific defocused depth in response to the spatial frequency of an observing object, so we observe an edge enhancement in this type of microscope. In experiment, we used OLS1100 laser scanning microscope (Olympus Co., Ltd.) with NA=0.95 in 100-power objective. Light source is Ar-ion laser of 488nm. We prepare rectangular samples which have 5.0 micron in width, and 50 nm in depth. We observed edge enhancement in auto-focus mode for the above samples. After measuring defocus characteristics of I-Z response we evaluate our theory in good agreement for the edge enhancement on the image of laser scanning confocal microscope.

This paper presents a fibre-based low coherence interferometric sensor developed by FOGALE nanotech. Based on the well-established principle of low coherence interferometry the sensor works as a comparator of optical path lengths. The optical path length in the measurement interferometer arm containing a target object is compared with the optical path length in an internal delay line. Multiple, partially reflecting surfaces of the target can be detected during one scan of the delay line. Measurement ranges are between a few mm up to 400 mm (optical thickness). The measurement zone can be placed at a distance of up to several meters away from the instrument's exit. The sensor reaches an absolute accuracy down to 100 nm over the full measurement range. The system has been applied both for the glass and for the optical industry. This paper focuses on innovative applications of the sensor in the optics manufacturing industry. First, the measurement technique and the system concept including the detection scheme and signal processing are explained. We present a modeling-based approach for the dimensional metrology of optical components (e.g. single lenses, windows, prisms) or complete lenses where the positions of all individual elements can be detected. A comprehensive propagation model including dispersion and phase effects is used to extract the distances from the optical path differences. Prior to a measurement, the optimum tailoring of the measurement beam is obtained by a simulation of the beam propagation through the target object. This ensures that each surface to be measured delivers a sufficiently strong signal. To illustrate our approach we present its successful application in the fabrication process of high-performance imaging optics.

One of the more challenging applications of optical metrology is real-time dimensional control and surface inspection in industrial applications, where strong requirements of cost, setup and applicability in adverse environments, greatly limit the number of applicable technologies. This paper shows an optic profilometer developed specifically for this purpose. This device, based on Conoscopic holography, is able to obtain a distance profile of a target in a single-axis scan; works from long distances and still keeps good resolution with a very easy and reliable setup. The first part of the paper introduces the working principles of Conoscopic holography and shows the sensor set-up. Necessary algorithms for obtaining the distance information are presented and the whole process is illustrated with real captures of test objects. The second part focuses on a real example of this technology applied in an on-line inspection system in steel continuous casting funded by the European Committee for Steel and Carbon, and which is currently working in Aceralia LDA steelmaking factory in Asturias (Spain). The system is placed in the process line and performs on-line detection of surface defects over hot steel slabs from a distance of 1200 mm. 100% of the production can be inspected without interfering with the process and without adding any delay.

In this paper we present a novel image-based 3D surface reconstruction technique that incorporates both reflectance and polarisation features into a variational framework. The proposed technique is suitable for single-image and multi-image (photopolarimetric stereo) analysis. It is especially suited for the difficult task of 3D reconstruction of rough metallic surfaces. An error functional consisting of several error terms related to the measured reflectance and polarisation properties is minimised in order to obtain a 3D reconstruction of the surface. We show that the combined approach strongly increases the accuracy of the surface reconstruction result, compared to techniques based on either reflectance or polarisation alone. We perform an evaluation of the algorithm with respect to single and multiple reflectance and polarisation images of the surface, relying on synthetic ground truth data. This evaluation also reveals which polarisation features should preferably be used in the context of 3D reconstruction of rough metallic surfaces. Furthermore, we report 3D reconstruction results for a raw forged iron surface, thus showing the applicability of our method in real-world scenarios, here in the domain of industrial quality inspection.

With computer generated holograms (CGH) the testing possibilities of interferometers for plane and spherical specimen is widened to the test of aspherical surfaces. The wave from a transmission flat or a transmission sphere is formed by the CGH to fit the surface of an asphere or a cylinder. The availability of suitable CGHs is often the limitation for the production of precision aspheres. JENOPTIK L.O.S. can provide a custom made CGH within a short time. We will show the design principles and the layout of the CGHs. The optical properties and the known limitations will be presented on the basis of measurements of aspherical surfaces.

At present several methods are adapted for the optical characterization of 3D surface profiles and forms, which are based on fringe projection, moire techniques, gray-code projection or photogrammetry [1-5]. According to principle and application the methods differ in accuracy of measurement as well as computation time or their technical complexity. Photogrammetry is a well-adapted method for the measurement of 3D objects. The basic idea of the method is to get the whole 3D matrix of real objects by capturing a number of 2D images. In this work we show a possibility for a rapid measurement (< 1 second) of the shape of a human face for medical applications (e. g. jaw-measurement). The surface structure of the human face is too homogenous to find homologous points by an ordinary illumination; therefore about 20 special statistical patterns are projected on the face and taken by cameras of a convergent stereo system. At present a digital projector is used but it is also possible to generate the statistical patterns by a classical one. To find the corresponding points in the pictures we use an enhanced correlation technique, which takes into account the characteristic intensity sequence of every single sensor element - unlike other correlation techniques, which avail a pixel area as a template. The influence of distortion - caused by the surface profile - is kept to a minimum. Therefore at higher profile gradients a denser point cloud is generated. At present the reachable accuracy is +/- 0.1mm (rms), which is sufficient for medical and other applications. But the demonstrated method is not restricted to evaluate the shape of human faces. Also technical objects could be measured.

Precision noncontact measurement of diameters of circular reflecting cylinders is an actual problem in industry, especially under inspection of rollers of frictionless bearings with their diameters up to 50 mm with measurement error no more than 0.5 μm. We have developed differential Fraunhofer diffraction method, which is appropriate for measurement of such diameters. Peculiarity of this method is rather measurement of gaps between two cylinder vertexes and two reference half-planes, than measurement of cylinder diameter by direct Fraunhofer method. Equivalent model for formation of Fraunhofer diffraction pattern by measurable object is presented. The proposed algorithm for processing of two diffraction patterns from gaps between cylinder vertexes and reference half-planes allows to determine objects diameter with inaccuracy of one- half micron. Experimental results are given.

Electronic speckle pattern interferometry (ESPI) can provide accurate contour measurement in the micron range and short measurement times far below one second. An advantage of this method is that illumination axis and observation axis can be identical in contrast to e.g. triangulation. Therefore ESPI represents an interesting alternative to other optical measurement principles used for surface profiling. Typical surfaces in industrial applications often show discontinuities, like steps or holes. An unambiguous measurement of such surfaces is only possible if the synthetic wavelength is chosen larger than the largest surface step. Since the noise level introduced to the measurement increases proportional to the synthetic wavelength, unambiguous measurements suffer from a loss of accuracy. The solution for this problem is the combination of two or more synthetic wavelengths. In contrast to other publications (hierarchical, pixel-wise approach or temporal phase unwrapping) our novel area-based approach uses only two synthetic wavelengths minimizing measurement time and device complexity. The use of areas instead of pixels allows a lower signal to noise ratio and a smaller number of synthetic wavelengths (in our case only two) respectively, compared to the hierarchical pixel based approach. In this paper we present the steps required during pre-processing (laser tilt and wave front compensation) and the opportunities and drawbacks of different algorithms used for the fusion of the two images gained from different synthetic wavelengths.

The need for standards in optical methods of strain measurement has been discussed previously and attention has switched to the creation of reference materials and standardised tests. Reference materials provide a means of calibrating a measurement system by comparison to a standard that is traceable to an international standard. In this way an unbroken chain of comparisons between the measurement system and the international standard with defined uncertainties in each comparison is created. A standardised test allows the performance of the measurement system to be assessed against a number of known quantities and such tests should be as challenging as the applications for which the measurement system has been designed. The preliminary design of a reference material for optical techniques of strain measurement are presented. Results obtained from the tests of these physical reference materials using digital image correlation, ESPI, grating (moire) interferometry, photoelasticity, strain gauges and thermoelasticity support the design hypothesis and have aided the refinement of the design. The first set of results produced with the new design showed remarkable correlation despite being obtained independently in four different laboratories in four different countries using six different techniques. Initial designs for a set of standard tests have also been created and some preliminary results will be presented. The concept of virtual standardised test materials has been introduced to allow the performance of the algorithms within a measurement system to be assessed so that a standard and comprehensive diagnostic and evaluation framework will be available to system designers, manufacturers and end-users.

A polarization phase stepping method is presented based on the use of a polarization plane rotator that establishes a relative phase shift between two counter-rotating circularly polarized beams. The phase step can be made relatively accurate, since it just depends on the accuracy with which the rotator is manufactured, and not on its orientation. The phase stepping method has been implemented in a single-camera two-channel shearing speckle interferometer, with two optical channels, and a relative phase step of π/2 between them.

Parametric acoustic arrays are built to generate highly directional audio sound by nonlinear interaction of ultrasound. Arrays especially built for applications at high audio sound pressure use the most effective ultrasonic transducer for airborne sound, i.e., a piezoelectric (PZT) bimorph. Since the individual transducer elements are very small (<16 mm in diameter) several hundred of them have to be combined to reach the desired audio sound pressure level. For high performance it is a prerequisite that all transducers radiate in phase. However, fluctuations in their properties result in according fluctuations in their phases. The construction of such a device therefore requires a non-intrusive technique for monitoring amplitude and phase of a three-dimensional sound field without creating any nonlinearity. TV-holography or Electronic Speckle Pattern Interferometry (ESPI) in its time-averaging mode combined with reference wave modulation has been applied for this purpose. The recordings represent a two-dimensional projection of the sound field integrated along the viewing direction. The three-dimensional field is obtained from many such projections through the sound field at different angles in a tomographic setup. Inversion by filtered backprojection yields the three-dimensional sound amplitude and phase that can be utilized to optimize transducer operation. The performance of such a system is demonstrated in the development of an ultrasonic array at 38.5 kHz. It is shown how the generation of highly directive audio sound has been improved by guidance from the optical results. The highly directional source of audio sound finally produced is needed for an application in monument research where loose areas in historical murals have to be identified.

The benchmarking of two optical strain measurement techniques, shearography and fibre Bragg grating (FBG) sensors, against theoretical strain calculations and resistance foil strain gauges (RFSG) is described. The test object used for the surface strain measurements was an ABS pipe that was hydrostatically loaded. A multi-component shearography instrument, capable of full surface strain measurement was used to determine the displacement gradients, from which the strain components were calculated. Six surface mounted wavelength division multiplexed FBG sensors were used to measure the axial and the hoop strains. RFGSs located on the surface of the pipe, adjacent to the FBGs, were used for comparison. Good agreement between theory and the axial and hoop strains determined by the different techniques was found.

We propose novel technique for z-distance measurement to an optically rough surface using dynamic speckles. The technique is based on the continuous frequency measurements of the power modulation of the spatially filtered scattered light. The dynamic speckle pattern is created when the laser beam scans the surface under study. We use an acoustooptical deflector to perform scanning the surface. Acousto-optical deflector provides the surface scanning at very high speed of 200 m/s. The complete optical-electronic system was designed and fabricated for measuring acquisition of two instant coordinates of the surface into a computer. The response time of the z-distance sensor in our first experiments is 16 microseconds. However, it is shown that the response of the sensor may be as fast as 100 nanoseconds. First measurements of the surface profile using fast scanning of the laser beam were experimentally demonstrated. The proposed technique can be very useful for monitoring the surface profile and/or vibrations of the fast moving or fast rotating surfaces in various industrial applications.

Sub-micrometer lateral resolution for the optical vibration measurement can be achieved when the scanned laser beam of a confocal microscope is the measurement beam of a heterodyne laser-Doppler vibrometer. Such a scanning system that allows vibration measurements up to 30 MHz is presented in this paper for the first time. We measured a minimum 1/e² -power spot diameter of 745 nm and, therefore, the vibration analysis of sub-micrometer mechanical structures is possible with our system. We demonstrate measurements on comb-drive fingers with 2 μm diameter, the tiniest structures available for us.

The random and bias errors of estimating Doppler frequency from zero counting technique and correlation technique based on correlation function zeros analysis are compared with the accuracy of conventional spectral analysis and ultimate accuracy given by Cramer-Rao lower bound. It is shown that spectral measurement technique has advantage over other techniques in low signal-to-noise ratio region, whereas zero crossing technique based on analysis of probability density ensures lower random and bias errors at high enough SNR. The correlation technique has relatively low random error but shows considerable bias error in the region of low and moderate SNR when information about Doppler frequency is obtained from first zero of correlation function.

The paper presents numerical and experimental investigations of two errors having pronounced influence on the results of interferogram intensity modulation calculations using temporal phase stepping, i.e., the phase step miscalibration and average intensity changes between component interferograms. Experimental studies of sinusoidal vibration mode patterns by time-average interferometry provide excellent verification of numerical findings.

In this paper we present a new family of MOEMS device, which can be used as high resolution optical resonant pressure sensor. The architecture contains a membrane loaded with an optical branch of a Mach-Zehnder interferometer (MZI), monolithically integrated on top of a Si substrate. The measuring arm of MZI is crossing the MEMS actuator based on a piezoelectric thin-film PZT transducer integrated on SOI membrane. The PZT transducer is excited by applying a sinusoidal voltage from a waveform generator. The working principle of MZI read-out is based on the change of effective refractive index of guided waves of MZI, induced by displacements of the deformable structure via the elastooptic effect and waveguide elongation. When the membrane operating at resonance frequency, the application of a pressure on the membrane produces a significant shift of resonance frequency corresponding to a loaded pressure. For the characterisation of dynamic characteristic study of microdevices, the advanced testing methods are necessary. The point-wise measurement system was combined with the multifunctional interferometric platform based on Twyman-Green microinterferometer, working in stroboscopic mode. The prototype of the pressure sensor was evaluated and measurement results are presented.

Significant progress in MEMS/MOEMS development requires new measurement methods. The pulse interferometry is one of the widely used technique for oscillating object analyses. It is based on object observation during the short laser pulse illumination. In the paper a new method for electronic time synchronization of oscillating objects, laser pulses and camera registration is proposed. The system is developed to measure the silicon micromembrane surface shape. Laser pulse mode properties and camera adaptation to a microinterferometer setup are considered in the paper. A complementary system oriented on the investigation of the relationship between object transient shape changes and oscillation phases is shown. Preliminary results of measurement of silicon membrane shape changes during oscillations are presented.

Specification of vibrational modes and amplitudes of structures are crucial issues in civil and mechanical engineering. Several techniques have been used for this kind of studies, including holographic interferometry, speckle interferometry and moire technique. But, for large-scale structures modal analysis technique is usually used. In this work we have used time averaging moire technique to study in plane vibrations of large structures. The study includes specification of vibrating modes and amplitudes of structures. The technique is applied by painting a suitable size linear sinusoidal reflectance pattern on the lateral surface of the structure. As the structure is put into vibration, using a wide-angle high-resolution digital camera, the image of vibrating pattern is recorded in an exposure time much larger than the vibration period. The visibilities of the image along a line parallel to the painted pattern line are derived by processing the reflectance distribution. By dividing the resulted visibilities by the visibility of the image of the static pattern we get the normalized visibility curve. The number of normalized visibilities equal to 1 provides the number of vibrational modes and the magnitudes of the visibility minima or the locations of the zero visibility give the amplitudes of vibration.

A radial in-plane electronic speckle pattern interferometer (ESPI) is used to measure residual stresses in combination with an indentation method. A semi-empirical mathematical model is developed to quantify the residual stresses from the radial in-plane displacement component measurement around the indentation print. Several tests were made in a specimen with different levels of residual stresses induced by mechanical loading. Correlation functions were fitted to tests results and are used to predict the residual stresses levels. This paper briefly presents the measurement principle, testing details and results of the performance evaluation. Finally, an uncertainty budget of the testing and measurement process was carried out. The tests presented here are not complete since they are restricted to only one material, oneaxis stress state, two indentation tip geometry and only one indentation force, but they are sufficient to encourage further development.

This paper shows the feasibility of applying speckle techniques as a non-destructive evaluation of the performance of ceramic high temperature superconducting materials. Firstly, Digital Speckle Pattern Interferometry has been applied to test these materials during service, with the sample cooled to liquid nitrogen temperatures, to detect where a hot spot will be generated. Surface degradation due to humidity has also been studied. Speckle Photography, whose optical setup is simpler, has been selected for this study.

Using the continuously refreshed reference frame in conjunction with the real-time subtraction allows time-averaged shearography to observe and to evaluate the vibrations in form of J02 -fringes in quasi real time. Since the fringe patterns are dependent on the vibration amplitudes, the resonance frequencies of the object can be detected due to the higher amplitudes in resonance. In this presentation a new technique is introduced to automatic detection of the natural frequencies without applying additional sensors by means of statistical method. This method is suitable for the automatic identification of flaws as well. An experimental investigation shows the detection of defects in a CFR material in this publication.

The metallic and concrete structures used in civil Engineering show their defects by the appearance of cracks. We report crack detection laboratory tests on a piece of armed concrete stimulated by acoustic waves. The feasibility of detecting non-emerging (hence invisible to a human observer) cracks is demonstrated. Our results show a good visual correlation between differential speckle interferometry, (a.k.a. shearography) and laser optical feedback imaging (LOFI). The advantages of shearography are its compacity, resolution and rapidity (it is a direct full view technique), but in this application, the information it provides is essentially qualitative. On the contrary the LOFI technique measures the difference of vibration amplitude on each side of the defect. Moreover its good sensitivity enables long-range measurement, but the image resolution and acquisition time depend on the tuning of scanning mirrors. The metallic and concrete structures used in civil Engineering show their defects by the appearance of cracks. We report crack detection laboratory tests on a piece of armed concrete stimulated by acoustic waves. The feasibility of detecting non-emerging (hence invisible to a human observer) cracks is demonstrated. Our results show a good visual correlation between differential speckle interferometry, (a.k.a. shearography) and laser optical feedback imaging (LOFI). The advantages of shearography are its compacity, resolution and rapidity (it is a direct full view technique), but in this application, the information it provides is essentially qualitative. On the contrary the LOFI technique measures the difference of vibration amplitude on each side of the defect. Moreover its good sensitivity enables long-range measurement, but the image resolution and acquisition time depend on the tuning of scanning mirrors.

In the frame of science in microgravity, the investigation of dendritic growth in a solidification process has been chosen as a test case in order to determine the ultimate performance and the limits of interferometric optical tomography, a well dedicated optical diagnostic tool for transparent media. In the frame of 3D-shape measurements on the morphology of transparent succinonitril directional solidification front, the relatively slow temporal evolution of the solidification front allow to record tomographic projections during 30 seconds without having modifications. This would lead to the possibility to use a rotating device holding the sample in order to record sequentially the different views or set of views of the tomograph. Interferometry through its high sensitivity to refractive index variation is able to discriminate between solid phase and its surrounding solution. Due to a high number of parameters involved in tomographic measurements and reconstruction, it was necessary to analyze step by step their influences. Representative static model scenes have been manufactured and in depth independently characterized by X-ray microtomography in air. The same model scenes have been inserted into a single arm phase-shift Mach-Zehnder interferometer again by rotating object in order to acquire up to 256 projections. Finally a tomographic reconstruction process has been performed, the results of which were compared to the reconstructions gained from the micro x-ray measurements. This work shows the potential of interferometric optical tomography as well as its limits.

Microelectromechanical systems (MEMS) are based on the generation and/or detection of deformations, motion and vibrations of thin mechanical structures having lateral dimensions in the micrometer to millimeter range. A number of technological issues commonly appear during the development of MEMS fabrication processes such as non uniform etching or deposition, surface roughening, stiction and stress-induced deformations. Likewise, as mechanical properties of thin films are difficult to predict, and are very variable with process parameters. Consequently, experimental data on the (thermo)mechanical and dynamical behaviour of MEMS and on their reliability are often required. In this paper, after a short description of the basic principles and performances of interference microscopy techniques, we review the capabilities of full field interference microscopy techniques for these applications. They are illustrated by various examples taken during the development of MEMS fabrication and packaging processes, and by results of measurements as function of temperature or under vacuum.

The replacement of aluminum by copper as interconnect metal in computer chips was and still is driven by the necessity to enhance the current density thus enabling higher packaging densities, a fact that correlates directly with faster, smaller, and less energy consuming devices. The usage of copper, however, leads to new technological challenges which are caused by its mechanical properties on one hand side and by its tendency to migrate into dielectric and/or semiconducting layers on the other hand side. To prevent such diffusion processes, very thin layers consisting of tantalum and tantalum nitride or titanium and titanium nitride are deposited. A non-contact, non-destructive, short-pulse-laser-acoustic method is used to determine the mechanical properties of the barrier layers and of the copper layer. Mechanical waves are excited and detected thermoelastically using laser pulses of 70 fs duration. For metals this leads to wavelengths of 10 to 20 nm and the corresponding frequencies amount to 0.3 to 0.6 THz. Thin film measurements of buried diffusion layers are provided and compared with Scanning Electron Microscopy measurements (SEM), Transmission Electron Microscopy (TEM), and Rutherford Backscattering Spectroscopy measurements (RBS). Results of a thermo-elasto-mechanical simulation are presented. Current limits of the presented method are discussed and future directions of the on-going research project are presented.

The micromechanical cantilevers have become a powerful tool for the study of forces on nanoscale and serves as the heart of the Atomic Force Microscope (AFM) and of all the Scanning Force Microscopes designs on this basic idea. These micromechanical cantilevers are forced to not negligible thermomechanical oscillations at room temperature induced by the thermal noise, which is a Brownian motion. These oscillations impose a fundamental limit to the accuracy of force detection setups in AFM. However these thermomechanical oscillations can be analyzed in order to obtain information about the tip-sample interaction. Several publications have been presented in the last years describing the evolution of the resonant frequency of the microcantilevers through the spectral power density in the case of non-contact behavior or by studying liquids or gas samples, with the standard optical lever technique. They have observed that it is impossible to detect the resonant frequency by this way in the case of contact with hard samples. Here we report on the investigation of mechanical sample properties by analysis of the thermomechanical noise of the first symmetric eigenmodes of a rectangular microcantilever. The presented work is the first study demonstrating the possible detection of the first flexural vibration modes of the microcantilever in contact with hard samples, by optical probing of the thermomechanical noise. By Analyzing the spectral density of the thermomechanical fluctuations attributed to the first symmetric flexural vibrational modes of the surface-coupled cantilever, the longitudinal stiffness of the tested sample can be obtained.

New developments in production technology increasingly focus on hybrid microsystems. Especially for systems with movable components, the process step of assembly is mandatory. In general, the accuracy of positioning of the parts has to be better than 1 μm. This makes specialized and automated production equipment necessary, which can lead to a conflict with the aim of flexibility of the range of products. Design for manufacturing is a well known remedy. Assembly aids are common practice today. These features of the workpieces bear no functionality for the end product but considerably ease certain process steps. By standardization of assembly aids generalized production equipment free from product-specific features could be developed. In our contribution, we demonstrate the photogrammetric determination of the positions of workpieces without reference to their exterior shape, using circular fiducial marks of 150 μm in diameter. The surface properties of the workpieces, however, still have an influence on image formation. As an example, the marks may be hidden by local specular reflections. A solution to this problem is to add an exclusive optical property to the fiducial marks to get an image with high contrast against the surface of the workpiece. In biology and medicine samples are stained with fluorescing dyes to enhance the contrast in optical microscopy. In fluorochromes, light of a characteristic wavelength is emitted after the absorption of light with a shorter wavelength. In our experiments we added a fluorochrome to a common photoresist and coated the surface of the workpiece with a thin layer thereof. Using photolithography as a patterning technique we generated fiducial marks with structures down to 25 μm. These marks can be identified by their characteristic emission wavelength under short-wavelength illumination. Only the fiducial marks remain visible in the images and processing these images is straightforward. The generation of fluorescing patterns by photolithography opens new possibilities for testing and process control in many fields of microtechnology.

We present a new type of point-diffraction interferometer specially designed for industrial use to obtain high immunity to external vibration encountered in the course of measurement process. The proposed interferometer uses thermally- expanded fibers instead of conventional pinholes as the point-diffraction source to obtain a high quality reference wave with an additional advantage of relatively easy alignment of interferometric optical setup. Vibration desensitization is realized through a common-path configuration that allows the influence of vibration to identically affect both the reference wave and the measurement wave and be subsequently cancelled out during the interference of the two waves. A new spatial phase shifter is also added to capture four phase-shifted interferograms simultaneously without time delay using a single camera to avoid vibration effect. Experimental results for a spherical concave mirror prove that the proposed interferometer is capable of providing stable measurements with a level of fringe stabilization of less than 1 nanometer in a typical workshop environment equipped with no excessive ground isolation for anti-vibration. Also, we verify that the proposed interferometer using a short coherence source is applicable to the surface metrology for defect inspection of transparent substrates such as liquid crystal display panels.

With the recent technological advances, there is an increasing need for measurement systems providing interferometer resolution for inspection of large quantities of individual samples in manufacturing environments.. Such applications require high measurement rates, robustness, ease of use, and non-contact systems. We show here that Digital Holographic Microscopy (DHM), a new method that implements digitally the principle of holography, is particularly well suited for such industrial applications. With the present computers power and the developments of digital cameras, holograms can be numerically interpreted within a tenth of second to provide simultaneously: the phase information, which reveals object surface with vertical resolution at the nanometer scale along the optical axis, and intensity images, as obtained by conventional optical microscope. The strength of DHM lies in particular on the use of the so-called off-axis configuration, which enables to capture the whole information by a single image acquisition, i.e. typically during a few ten of microseconds. These extremely short acquisition times make DHM systems insensitive to vibrations. These instruments can operate without vibration insulation means, making them a cost effective solution not only for R&D, but also especially for an implementation on production lines. Numerous application examples are presented in this paper such as shape and surface characterization of high aspect ratio micro-optics, surface nanostructures, and surface roughness.

Laser cladding is an innovative surface treatment process which has several advantageous properties like a reduced material distortion compared to conventional techniques. In this technique the cladding material is fed as a powder through the laser beam to the melt pool. For an optimisation of this process with respect to treatment time and efficiency a characterisation of powder size, distribution and velocity is crucial. Holographic particle image velocimetry is a powerful tool for characterisation of particle distributions with respect to size, 3D-position and velocity. Due to the holographic recording principle 3D-information can be evaluated from just one hologram. Its major drawback, the time-consuming development and repositioning of the hologram plates, can be avoided using the well-known technique of digital holography. In this case the hologram is recorded by a CCD-camera and reconstructed numerically. Common digital holographic particle measurements are performed using an inline configuration in order to minimise the experimental effort. In this case the measurements are limited to low-density particle fields due to increased noise generated by an overlap of real and virtual image in the reconstruction process. In this paper the application of off-axis digital holographic particle velocimetry to the characterisation of powder distributions in a laser cladding process is presented. Besides the experimental realisation special emphasis is given to the numerical reconstruction of the 3D-position and velocity of the particles. In extensive tests the suitability of the proposed technique is demonstrated. In the powder measurements up to 300 particles are detected with diameters of about 100μm and characterised with respect to position in a volume of about 1cm3 from just one hologram. In addition the speed of the particles is determined by double pulse measurements.

The role of the assist gas blown by a nozzle during the laser cutting process of ceramics is very important as a complex flow field is created by the interaction with the material. Flow visualization provides valuable information related with the properties and characteristics of the process in order to clear up misconceptions and as a first step towards the nozzle optimization. Optical methods as Schlieren or interferometry are suitable techniques for this task as well-known non-intrusive full-field methods utilized for analysing fast transient flow phenomena. In this work a Mach-Zehnder interferometer is employed in order to characterize a Laval nozzle by studying the shock wave patterns in a free gas jet as a previous step in order to study the complex interaction of the gas flow against a transparent model of the processed material. The optical phase is extracted from the obtained high-frequency fringe pattern by the Fourier Transform Phase-Difference Method. Disturbing effects are cancelled by proper combination of high-frequency fringe patterns obtained with and without gas flow. The shock wave pattern is analyzed for different geometrical configurations and operating pressures.

In the present study, an experimental investigation is conducted for the research of the turbulent open channel flow field at the three directions with the aid of one component Laser Doppler Anemometer and x Hot Film sensors. The instrumentation is used in an efficient manner for the extraction of three turbulent statistics with one measurement. The application of the present technique is conducted on fully developed uniform open channel turbulent flow and on flow with suction from the bed. With the aid of assumption for zero correlation between velocity and direction fluctuations the required number of measurements in the plane of flow direction for turbulent statistics is reduced. Using the Hot film sensor in the streamwise- spanwise orientation and with the LDA beam plane inclined in streamwise - vertical plane for the extraction a component of streamwise velocity direction, the three turbulent statistics are estimated. Also, with the assumption of randomness of velocity fluctuations of the open channel flow in the zero correlation assumption, the dependence of turbulent statistics with the angle is possible to be calculated. The influence of suction from the bed on the uniform open channel flow, alters the turbulent flow field characteristics and in the present paper the distribution of turbulent intensities are presented for various suction rates in the flow depth. In the form of covariance and autocovariance, angle dependence is examined for uniform flow and for flow with suction from the bed.

When a light coming from a circularly polarized heterodyne light source incidents on an optical material, a phase difference between s- and p- polarization components of the reflected light occurs. This phase difference can be measured accurately with the heterodyne interferometry. The measured data are substituted into the special equations derived from Fresnel equations, the refractive index can be estimated. This method bears both merits of a common-path interferometer and a heterodyne interferometer. The refractive indices of three optical glasses and two birefringent crystals were measured to show the validity of this method.

Zernike polynomial fitting has been the commonplace alternative for assigning a measured wavefront a given shape. However, Zernike polynomials have intrinsic limitations under given conditions, mainly in complex wavefronts with for instance decentered double-peaks or with relevant undulations. The main goal of this paper is analyzing an alternative to Zernike fitting based in B-Spline fitting, comparing the strengths and weaknesses of each representation when applied to wavefront fitting. Simple and complex wavefront cases will be presented and studied, and the quality of their fitted representations using Zernike and B-Spline polynomials will be compared, presenting the main factors relevant in their comparison. Moreover, the case of random white noise added to the estimated data will allow an insight into the expected behavior of both representations when applied to experimental data.

Digital Signal Processing (DSP) processors are microprocessors designed to perform digital signal processing-the mathematical manipulation of digitally represented signals. In this paper, the novel Infrared Image Processor (IIP) and the pattern process algorithm run in the processor are designed with DSP chips ADSP-TS201S manufactured by ADI (Analog Device Inc.). There are two signal channels within the IIP. The signals passed through the channels may be same or not. In this case, it is different. There are four pieces of DSPs which utilized and parallel procedure and serial procedure. The special character of the algorithm is the neural network method.

A new approach for unwrapping phase maps, obtained during the measurement of 3-D surfaces using sinusoidal structured light projection technique, is proposed. “Takeda's method” is used to obtain the wrapped phase map. Proposed method of unwrapping makes use of an additional image of the object captured under the illumination of a specifically designed color-coded pattern. The new approach demonstrates, for the first time, a method of producing reliable unwrapping of objects even with surface discontinuities from a single-phase map. It is shown to be significantly faster and reliable than temporal phase unwrapping procedure that uses a complete exponential sequence. For example, if a measurement with the accuracy obtained by interrogating the object with S fringes in the projected pattern is carried out with both the methods, new method requires only 2 frames as compared to (log2S +1) frames required by the later method.

The interconnection between geometry of biotissue structure with their polarization properties has been studied. It has been shown that for physiologically normal biotissues polarization properties of radiation scattered on architectonic nets formed by protein fibrils possess the fractal character. Pathological changes of biotissues architectonics are accompanied with the transformation of self-similar structure of Mueller-matrix images into stochastic and statistic ones.

This paper presents a method of pattern design for a 3D vision sensor, which is based on the principles of color-encoded structured light, to improve the reconstruction efficiency. Since an ordinary structured light system using an LCD projector needs to take several images (usually 8-12 images) for recovering the 3D scene, as a result its speed is limited and applications are restricted in acquisition of static environment. For dynamic cases, the 3D measurement is desired to only capture a single image. To realize this, a new method is to use a color projector which can be controlled by a computer to generate arbitrary desired color patterns. A problem of the color encoded projection is the unique indexing of the light codes in the image. It is essential that each light grid be uniquely identified by incorporating the local neighborhoods in the light pattern so that 3D reconstruction can be performed with only local analysis of the single image. This paper proposes a method in design of such grid patterns. Experiments are provided to demonstrate the proposed method with two, three, and four different colors. The maximum possible square matrices are illustrated.

We investigate the focusing action of refractive microlens based on the rigorous electromagnetic theory by boundary element method. We numerically simulate total electric-field patterns, the electric-field intensity distributions on the focal plane, and their diffractive efficiencies at the focal spots for describing the focusing behaviours of these microlenses with continuous and multilevel surface-envelopes. Focusing action of incident beam with a certain angle of inclination is indagated as well. The present numerical and graphical results may provide an useful information for the analysis and the design of refractive elements in micro-optics.

Inteferograms are made by interfering wave fronts and hence contain important information about them. Analysis of interferogram requires the identification of all the fringes and their exterma. Here an algorithm for computer tracing of interference fringes is described. The method uses a Fourier filter for removing high frequency noise, a local averaging for binarization of images not having uniform intensity distribution, scanning the interferogram locally both horizontally and vertically to determine the type of the scan, local application of simultaneous horizontal and vertical scan for tracing of complicated fringe patterns and removal of the noise from the traces by determining the number of connected pixels. The poroposed algorithm was found to yield good result even for high noise images.

A new technique for processing of noisy fringe patterns with complex fringe shapes is presented . The technique is based in exploiting the capabilities of digital filters, treating the fringe-pattern as a signal to be processed. The main parameters required for designing the filter, and the application of the design methodology to a particular experimental fringe pattern are described in detail. To conclude, the designed filter is applied to experimental noisy fringe-patterns both from complex and simple wavefronts, which are processed without a single change in the parameters of the algorithms. The procedure is completely general, with a very small computational cost, and may be extended to any noisy fringe-pattern to be processed given the fringes are still visible.

A focus sensor on the basis of a hologram laser unit was developed and successfully tested in a nanopositioning and nanomeasuring machine as a zero indicator. The high resolution of the focus sensor is due to a high-precision optical adjustment and special solutions incorporated into the electronic parts. Thus, any sensor malfunctions caused by back-reflected light inside of the assembly could be completely avoided by means of the special high-frequency modulation and laser power stabilization. Common mode noise reduction provides the high SNR of the output signals. The measurements were made according to a dynamic principle by permanent difference formation between the output signal of the focus sensor and the length value of the z-interferometer of the nanopositioning and nanomeasuring machine. The measuring results are presented, and further possibilities of application are outlined.

As in the classical holography, a major issue in digital holography is the enhancement of the resolution of the digital holograms. It means not only the enhancement of the image quality, but the extension of the upper measuring range too. One natural way can be the application of higher resolution recording devices. Unfortunately the price of a doubled resolution camera is approximately fourfold. In the presentation a different way of the resolution enhancement is shown. The resolution enhancement (building the super image) is based on the building of well sampled so called super images from a set of under sampled but dithered input images. Such methods are originated from the drizzle method, and from the Fourier spectrum combination method. Using these methods not only the resolution of the digital hologram can be increased, but the object distance also can be dramatically shortened.

Measurements of very small phase changes in optical measurement techniques are usually performed by interferometric methods that are based on evaluation of interference patterns, which correspond to a phase change of the investigated wave field. If values of the phase change are small, it is difficult to determine accurately the phase values, and one needs very expensive measurement systems. Our work presents a simple method for evaluation of small phase variations that uses the interference of polychromatic light. The phase change affects the color of the interference pattern, and color of the interference pattern corresponds to a specific phase change that can be evaluated using colorimetric analysis. We describe and analyse the colorimetric phase evaluation method in our work. The proposed method offers accurate results and it is suitable for practical utilization in optical industry.

Wavelet transform analysis of projected fringe pattern for phase recovery in 3-D shape measurement of objects is investigated. The present communication specifically outlines and evaluates the errors that creep in to the reconstructed profiles when fringe images do not satisfy periodicity. Three specific cases that give raise to non-periodicity of fringe image are simulated and leakage effects caused by each one of them are analyzed with continuous complex Morlet wavelet transform. Same images are analyzed with FFT method to make a comparison of the reconstructed profiles with both methods. Simulation results revealed a significant advantage of wavelet transform profilometry (WTP), that the distortions that arise due to leakage are confined to the locations of discontinuity and do not spread out over the entire projection as in the case of Fourier transform profilometry (FTP).

Spectral modulated interferograms (channeled spectra) characterize dispersion of optical samples and allow measuring distances and displacements. Useful information is contained in spectral fringe frequency and phase that can be evaluated dynamically by the extended Kalman filtering method based on recurrence prediction-correction processing procedure. The method provides direct dynamic estimates of unwrapped fringe phase within single fringe sample series. The accuracy of the extended Kalman filtering method has been investigated experimentally by processing recorded spectral interferograms.

A compact, solid-state, diode-pumped laser at 532 nm stabilized in frequency on one of the electronic transitions R(56) 32-0 of the absorbing molecule ¹²⁷I₂ has been developed and investigated. The active medium is Nd:YVO₄ and a KTP crystal is used for intracavity frequency doubling. Third-harmonic techniques are used for frequency stabilization with an external iodine cell. Electronic units are designed for the power supply, the five temperature control systems of the laser elements and of the iodine cell finger, and that of servo electronics for frequency stabilization. The frequency stability in terms of an Allan variance is 2×10^-12, 1×10^-13 and 3.1×10^-14 at the time intervals of 0.1 s, 10 s and 100 s, respectively. The laser output power at 532 nm is greater than 4 mW. Such lasers will find wide application in laser displacement interferometry, in laser interferometers for absolute gravimeters and in laser spectroscopy. These lasers can also be used as portable secondary wavelength (frequency) standards at 532 nm.

This contribution presents a new algorithm to extract a measure of the quality of honed cylinder bores based on 2D intensity or topography data, enabling thus an objective assessment of their surface texture. The method is based on an adaptive separation of the surface data into two complementary components-the groove texture and the background data. Following, from these separation results, a scalar feature is computed that describes the texture quality compactly and reliably. Based on a series of fax film replicas of real honing textures showing different degrees of quality, the principle of the algorithm is illustrated. Moreover, the usefulness of the proposed approach is demonstrated by comparing classification results based on the new measure with ratings of experts. In all cases, a correct class assignment could be achieved.

A simplified version of the liquid mirror setup to serve as planarity reference standard is described in detail. Particulars of the mounting, maintenance and use of the mirror are provided. A series of measurements over a diameter of 90 mm is reported; the resulting expanded uncertainty for the peak-to-valley achieved in experiments is 7 nm (2σ).

The adaptive Shack-Hartmann sensor (ASHS) is a modifictaion of the conventional Shack Hartman sensor which uses a dynamic Liquid Crystal Display (LCD) in replacement of the static diffractive or refractive microlens array. The LCD is used to display an array of Fresnel microlenses. The microlenses can be adapted to the wavefront in order to enhance measurement accuracy and dynamic range. Because of the relatively large pixel of the LCD the size of the microlenses is larger than in a conventional sensor. The number of microlenses is limited by the resolution of the LCD and therefore smaller than in a conventional sensor. Certain considerations are required when restoring the wavefront phase values with the reconstruction algorithm. We present two matrix inversion reconstruction methods: The classic Zernike approach and a BSpline algorithm. We will compare these two methods on the basis of fit accuracy, reconstruction time and the effect of noise and missing data points.

A new approach for measurement of wire diameter lying in the range of 200 to 450 microns is proposed and demonstrated. The approach is based on evaluation of phase-correlation based similarity measure for two identical order fringes of a diffraction pattern. Diameter of wires is estimated by determining separation between identical order fringes. Robustness of the approach to noise is enhanced by using Gaussian and singular value decomposition based filtering. Implementation of the method with an off-the-shelf digital photo camera for acquiring experimental data from steel wires and thin slits have demonstrated an accuracy far better than 0.5% of dimension.

The structured light vision system consists of a CCD camera and a digital projector. Calibration of such a vision system plays an important means of accurate 3D reconstruction of a scene. However, the projection model for both the camera and projector is very complicated because of distorted and nonlinear factors in it. It is unlikely to accurately model a camera with only a few parameters even considering some lens distortions. In order to simplify the system calibration and 3D reconstruction, this work presents a new calibration method that is based on neural network and brought forward according to the characteristics of neural network and vision measurement. The relation between spatial points and image points is established by training the network without the parameters of the camera and the projector, such as focus, distortions besides the geometry of the system. The training set for the neural network consists of a variety of lighting patterns and their projected images and the corresponding 3D world coordinates. Such a calibration method has two distinct advantages. It possesses the complicated nonlinear relation between two-dimensional information and three-dimensional information with the neural network, which can include various kinds of distortion and other nonlinear factors during the imaging period. Experiments are carried out to demonstrate and evaluate the procedure. From the result of training we can find out that through the neural network, it may avoid non-linear operation and obtaining the three-dimensional coordinates directly.

As a key specification of the beam quality control, the profile of the optics requires hi-precise testing, which is indispensable during the R&D of high power laser drivers. Currently, the commercial interferometers provided by such companies as Veeco , Zygo and 4D in US and Fuji in Japanese are widely used in profile testing of optics. However, during our practice, a fairly good accordance can not be found after a series of the profile tests of the optics. Generally, there’re certain fluctuations or even remarkable difference among the testing results occurring in the testing results compared with the design specifications. In order to improve the existing poor accordance of the testing results of profile specifications of the optics, and in accordance with our repeated experiments, the Main factors that affect the profile testing are presented respectively, as well as their corresponding impacts upon the profile based on the clarified evaluation parameters and unified testing principles, which are of significant reference value to standardize the testing method of optics profile and to strictly control the optics quality.

An experimental technique for testing the image quality of microscope objective lenses and optical systems is described. Our work deals with a theoretical analysis of properties of a small and compact shearing interferometer, which was designed, manufactured and tested on several microscope objectives. The designed shearing interferometer can be used for testing the quality of optical systems, e.g. microscope objective lenses and camera lenses. The proposed shearing interferometer enables to determine the residual wave aberration of the tested optical system (e.g. microscope objective lens). The wave-front deformation can be analysed using colorimetric methods or standard phase evaluation techniques for interferometry. The device is characterized by very small dimensions, which provide its easy portability. The described compact shearing interferometer is practically insensitive to vibrations and the mechanical design is also very simple. The proposed evaluation method offers very accurate results and it is suitable for practical utilization in optical industry. The interferometer is suitable for testing laboratories and service engineers in the field of optical microscopy. The asame inferometer can also be used not only for wave abberation measurement, but also for measurement of the modulation transfer (MTF) of tested optical systems.

A 500-mm-aperture wavelength-tuning phase-shifting interferometer has been developed in FOERC applied to the measurement of large optics. Also it can switches to a smaller 130-mm-aperture. We describes in detail the optical and mechanical design as well as calibration technique of phase shifter and phase-shifting algorithm design. A Zygo 4 inch standard reflective flat is used to evaluate the accuracy and repeatability of our wavelength-tuning phase-shifting system.

The problems of topography of surfaces are very important in various parts of science and engineering. Several approaches exist for surface figure and roughness measurement. The measurement methods can be divided into two distinct categories, contact and non-contact techniques. Our work describes a relatively simple method for topography measurements that uses special optical systems (hyperchromats) with a linear dependence of longitudinal chromatic aberration on the wavelength of light. The aim of this work is to show a possible application of hyperchromatic optical systems for topography of surfaces. The work describes a basic analysis of parameters of hyperchromats, i.e. optical systems with large longitudinal chromatic aberration that is in our case linearly dependent on the wavelength of light. On the basis of the performed analysis, it can be designed such optical systems (optical sensors) that permit to perform measurements of topography of surfaces, i.e. determine a figure or roughness of surfaces. The sensor uses polychromatic light and relatively simple experimental arrangement. The proposed measurement technique seems to be quite simple and cost effective with respect to other measurement methods.

The paper presents the results of an on-going research regarding the optical scanners with rotating, plane or polygonal mirror, used in the on-line, dimensional industrial measurements. Altough this particular area of applications is considered, the results that have been obtained are also valid for others, different kinds of applications of the laser scanners. The parameters of the two devices considered are deduced, in a comparative look, in a rigouros mathematical approach, different from the one in the state-of-the-art. The sources of errors in the scanning process are analysed, and from this, several new solutions for the reducing or for the compensation of the errors are obtained. The main problem presented is the non-linearity of the functioning characteristic and the possibilities of linearizing it - both for the plane and for the rotating mirror device. From the discussion, a designing calculus of the polygonal scanners results, on different cases, with regard to the requiered value of the duty-cycle. The study is completed, for each scanner, with an experimental part, that verifies the theoretical results.

3D surface measurement of machine parts is challenging with the increasing demands for micron level measurement accuracy and speed. Optical Metrology based techniques using stereovision face unique challenges in feature extraction due to the complexity of the machine parts and surface finish. For complicated parts, structured laser light is projected on the surface to generate unique or reference features for stereo reconstruction. The induced laser light on the surface is scattered due varies surface phenomena (light scattering, multiple reflections). These scattered and diffused laser lines induce new features on surface, which misguides the surface reconstruction. While targeting micron level accuracy, sub-pixel feature extraction is also effected by the speckle noise, biasing due to sampling, shape etc. In this paper, we propose new method of improving the accuracy of 3D surface reconstruction on metallic shining surfaces. The proposed template based guidance approach with tangent based feature extraction improves the accuracy of detection in the effected regions by 30%.

In the paper we present the prototype of a straightness measuring device that uses a frequency stabilized Zeeman He-Ne laser. The He-Ne laser line is split by Zeeman effect into two circularly polarized laser beams. The frequency of the radiations differ of 1,2 MHz. The surface stabilized ferroelectric liquid crystal cell is used to stabilize the laser frequency. As the result of the laser frequency stabilization the power of both radiation is equal. The circular polarizations of two laser beams are converted into two linear polarizations perpendicular to each other. The two laser beams pass close to the measured axis. Along the axis the analyzing probe is moved. The analyzing probe changes the ratio of the power of the horizontal to the vertical polarization. This ratio is analyzed by the receiver composed of the ferroelectric liquid crystal switcher, the polarizer and the detector. The straightness of 2 m long optical bench was measured with this techniques. The resolution of 0,1 μm and the accuracy of 0.5 μm were obtained. The accuracy of presented technique is not so good as in the methods using laser interferometer but is comparable with methods using PSD, quadrant detectors or CCD at the same time offering bigger resolution.

3D measurement of the shape of rough structures can be realised with structured light illumination techniques. Several problems can arise while measuring complex object geometries with these techniques. Complex objects are characterized, f.e. by deep holes, walls, concave and convex corner-like shaped surface structures. When illuminating the object, one part of the object can "illuminate" another one, yielding locally spurious fringe patterns. Due to these spurious fringe patterns the phase values are strongly distorted significantly increasing the measurement noise locally. Here we propose methods how to detect and to avoid these spurious fringe patterns. The idea is to use the overestimated information which is contained in the graycode and the sinusoidal intensity distribution. On the basis of this procedure, an operator is defined which results in a mask operation. With this new method we can reduce the noise amplitude. In this paper, the detection and reduction of the illumination effect using this operator will be demonstrated while measuring different object geometries.

In this paper we present an optical method based on speckle pattern correlation for measurement of the topography of a surface of an object under investigation. When this object is illuminated with coherent laser beam the arising speckle pattern bears information about the height profile of the object. The resolution of this method is influenced by geometrical parameters of optical measurement set-up. The designed experimental set-up for the measurement of the slope of the object with rough surface is described. Achieved results are presented in comparison with theoretic values.

A peak power of 286-TW Ti:sapphire laser facility referred to as SILEX-I was successfully built at China Academy of Engineering Physics, for a pulse duration of 30 fs in a three-stage Ti:sapphire amplifier chain based on chirped-pulse amplification. The beam have a wavefront distortion of 0.63μm PV and 0.09μm RMS, and the focal spot with an f/2.2 OAP is 5.7μm, to our knowledge, this is the best far field obtained for high-power ultra-short pulse laser systems with no deformable mirror wavefront correction. The peak focused intensity of ~1021W /cm2 were expected.

Specific features of the formation of local and statistical polarization structures of laser radiation scattered in phase-inhomogeneous layers (PIL) of biological tissue (BT) were studied. The distribution of azimuth and eccentricity of boundary field polarization was found to correlate with the orientation-phase structure of multifractal PIL. A method of polarization phase reconstruction of BT architectonics was suggested.

Accurate estimation of displacement between successive images is a significant topic in the measurement of in-plane vibrations of microscopic objects such as micro-actuators. Actual subpixel motion estimation algorithms require the interpolation of interpixel values which undesirably increases the overall complexity and data flow and deteriorates estimation accuracy. Methods that do not use interpolation for achieving subpixel accuracy are scarcer in the literature. One approach for subpixel movement estimation without interpolation is based on phase correlation algorithm. This algorithm estimates the relative shift between two image blocks by means of a normalized cross-correlation function computed in the 2-D spatial Fourier domain. Indeed, the method is based on the Fourier shift theorem. The cross power spectrum of two images, containing subpixel shifts, is a polyphase decomposition of a Dirac delta function. By estimating the sum of polyphase components one can then determine subpixel shifts along each axis. Phase correlation is the state of the art for interpolation-free subpixel shift measurement between two frames, but this method is strictly limited to subpixel shifts. So, we have implemented this method using a standard optical microscope in order to observe subpixel translations with high spatial resolution measurements (down to 1 nm in the best cases). In this paper, we propose an application of this method to characterize the vibration mode shapes of a small silicon beam used in near-field acoustic microscopy. Harmonic movements of a few tens of nanometers are measured and presented.

Current design, analysis and control engineering applications require effective experimental methodologies and tools for determination of displacement and strain fields as well as material characterization. One of the most important problem in engineering objects is proper design and quality of joints between elements in the form of welds, glued and riveted joints and many others. Specificly the fatigue and fracture mechanics problems in joints are difficult to analyze numerically, therefore they need experimental support. In the paper we present the results of static, dynamic and fatigue experiments performed by grating (moire) interferometry systems. These full-field optical extensometers provide information about in-plane displacement field (u,v) and strain fields (εx, εy, γxy) in the region of a joint subjected to various modes of loads. It is shown that proper design of full-field extensometer (insensitivity to vibration, good quality of interferogram, automatic analysis of long series of interferograms) allows to use it efficiently directly at conventional loading machine in workshop environment and for long term fatigue tests. In the paper we present results of studies of: conventional laser welds (static, fatigue tests), friction stir weld (static tests), riveted joint (static, fatigue tests). The methodology of determination of local material constants in different zones of a joint (inc. Poisson ratio, Young’s modulus) is given. The future trends in hybrid experimental-numerical analysis of joints in conventional and novel material are discussed.

This communication proposes the description of an optical method for thermal characterization of MEMS devices. The method is based on the use of an intensified CCD camera to record the thermal radiation emitted by the studied device in the spectral domain from 600 nm to about 850 nm. The camera consists of an intensifier associated to a CCD sensor. The intensification allows for very low signal levels to be amplified and detected. We used a standard optical microscope to image the device with sub-micron resolution. Since, in close infrared, at very small scale and low temperature, typically 250°C for thermal MEMS (Micro-Electro-Mechanical Systems), the thermal radiation is very weak, we used image integration in order to increase the signal to noise ratio. Knowing the imaged materials emissivity, the temperature is given by using Planck’s law. In order to evaluate the system performances we have made micro-thermographies of a micro-relay thermal actuator. This device is an “U-shape” Al/SiO2 bimorph cantilever micro-relay with a gold-to-gold electrical contact, designed for secured harsh environment applications. The initial beam curvature resulting from residual stresses ensures a large gap between the contacts of the micro-relay. The current flow through the metallic layer heats the bimorph by Joule effect, and the differential expansion provides the vertical displacement for contact. The experimental results are confronted to FEM and analytical simulations. A good agreement was obtained between experimental results and simulations.

Narrowband ultrasonic surface acoustic waves are of the greatest current interest for the nondestructive testing of thin-walled members and shell structures like plates, pipes, bridge girders, cans and many others. The measurement and characterization of ultrasonic displacement fields of Lamb waves by pulsed TV holography (TVH) is presented. Narrowband ultrasound is generated in a few millimeters thick aluminum plate by the prismatic coupling block method using a tone-burst excitation signal in the range of 1MHz. At this frequency, the plate supports only a few Lamb wave modes, mainly the A0 and S0 ones. The simultaneous presence of these modes produces a beating clearly detectable as a spatial amplitude modulation. Our self-developed TVH system performs the optical phase evaluation by the Spatial Fourier Transform Method and renders the instantaneous out-of-plane mechanical displacement field along the whole inspected area. From this field, the wavenumber of each Lamb mode can be obtained and, by combining them with the value of the ultrasound frequency and with the Rayleigh-Lamb theoretical frequency spectrum, information about the elastic constants of the specimen material is obtained.

In the industry of sintered automobile synchronizer hubs, as in many others, a fast on-line measurement system of the production is a very important tool for production and quality control, enabling among others: extended quality control to all the production, lower start-up times, improved knowledge of the process and influence of its parameters and database management of the information. In this paper we describe an on-line optical measuring system that is able to inspect 100% of the production, making special emphasis on how the resolution and accuracy of the measurement could be compromised by factors that are not related to the sensor itself, as well as how to correct them. The paper also describes how to validate such a system according to the ISO 5725 standard.

Autocollimators comply with the requirements of different metrological measurement tasks. These instruments are compact, versatile and easy to use. Angle deviations of prisms, polygons, e.g., are measured with autocollimators. If calibrated electronic autocollimators are used, then the measurements can be performed with uncertainties down to 0.01 arc sec. However, the uncertainty might be increased by one order of magnitude or more if surfaces with small apertures, aberrant surfaces or surfaces placed at long working distances are measured. To define the measuring window, respectively the limiting parameters, a software based model of the optical system was implemented. Aberrations, diffraction, temporal and spatial coherence were taken into account. To increase the measurement range, now defined by simulations of the optical system, a phase grating technology can be used. Simulations assuming a phase grating technology show a significant enhancement of the autocollimators imaging properties. This enables a significant reduction of the uncertainty at difficult measurement tasks as mentioned above. The state of the art of simulations will be presented and the optical background will be described.

The results of the R & D activity of TDI SIE SB RAS in the field of the 3D optical measuring technologies and systems for noncontact 3D optical dimensional inspection applied to atomic and railway industry safety problems are presented. This activity includes investigations of diffraction phenomena on some 3D objects, using the original constructive calculation method, development of hole inspection method on the base of diffractive optical elements. Ensuring the safety of nuclear reactors and running trains as well as their high exploitation reliability requires a 100 % noncontact precise inspection of geometrical parameters of their components. To solve this problem we have developed methods and produced the technical vision measuring systems LMM, CONTROL, RADAR, and technologies for noncontact 3D dimensional inspection of grid spacers and fuel elements for the nuclear reactor VVER-1000 and VVER-440, as well as automatic laser diagnostic COMPLEX for noncontact inspection of geometric parameters of running freight car wheel pairs. The performances of these systems and the results of industrial testing are presented and discussed. The created devices are in pilot operation at Atomic and Railway Companies.

This work presents the progress made in primary level photometric measurements at the National Metrology Institute of Turkey (UME). A Cryogenic Radiometer (Oxford Instruments Radiox) was employed in the optics laboratory as an absolute primary standard. Temperature-controlled filter radiometer constructed from three-element silicon trap detector, band-pass filters and precision aperture. Filter radiometers were calibrated using the cryogenic radiometer at discrete laser wavelengths of vertically polarized tuneable Ar+, fixed He-Ne and Nd: YAG (with second harmonic) laser sources. Luminous intensity unit of candela was realized with an expanded uncertainty of 2.88x10-3 and photometric scale was re-established depending on this detector-based realization. Candela realization was performed on optical bench using traditional Osram Wi41/G type incandescent light source and an absolute filter radiometer. Other derived units of photometry that are luminous flux, illuminance, color temperature and luminance are derived from candela through various photometric measurements including some homemade devices of laboratory.

The measurement of the surface cleanliness is a problem of great importance in many industrial and technological processes. Existing methods are based on laboratory procedures, they are not performed in real time, they cannot be automated, and usually they are restricted to a small portion of the sample. In this work we describe a new method for real time measurement of the amount of dirt deposited on a surface. It relies in the ablation of the dirt film by means of a short laser pulse and the subsequent measurement of the sound emitted. The intensity of the sound results proportional with the amount of dirt and provides a direct measurement of the cleanliness of the surface. The method requires a reference for calibration that was developed based in a uniform distribution of points printed on white paper or a transparent film. The point size and density can be easily modified providing a homogeneous, uniform and reproducible standard for the total amount of dirt measurement. Based on this method, we designed patented (P000101241-Argentina and 6.546.784 EEUU) and developed the first industrial instrument (ELMES) for on-line determination of the cleanliness degree of manufactured cold rolled steel plate bobbins.

The demand on quality of optical surfaces is increasing from year to year. Computer controlled polishing is one way to fulfill these demands. The process depends on the error-profile of the optical surface. In this paper the usage of the TII measurement machine is discussed to manufacture optical surfaces.

In order to establish a particle number concentration standard and the related calibration technology in liquids, a new particle counter based on the simultaneous detection of scattered light and fluorescence was examined. Sample particles from 2 to 10 micrometers in diameter were dyed. By making use of the fact that bubbles make no coincidence signals between scattered light and fluorescence on the other hand particles make coincidence signals, we could distinguish particles from bubbles. And we can establish the particle number concentration and the calibration technology in liquid. Using this system, fluorescence could be measured at 525 nm, 625 nm, or 675 nm as well as at 575 nm. To examine the electric counting error and error due to stray light counting, the four channels were compared. The difference in counting between each of the channels was less than 0.1% in relative standard deviation. To evaluate the reliability of the particle counts obtained with this system, the obtained values were compared with counts obtained using a microscope. With a microscope, the total area was manually scanned for the total counting to reduce the statistical uncertainty. The results of both methods were in good agreement, with a counting efficiency of 100% plus or minus 10% for 2 micrometer particles, and of 100% plus or minus 5% for 10 micrometer particles. The difference in the repetition of the new counter was less than 1%.

Determination of the actual nonlinear inelastic response mechanisms developed by civil structures such as buildings and bridges during strong earthquakes and post-earthquake damage assessment of these structures represent very difficult challenges for earthquake structural engineers. One of the main reasons is that the traditional sensor can't serve for such a long period to cover an earthquake and the seismic damage location in the structure can't be predicted in advance definitely. It is thought that the seismic damage of reinforced concrete (RC) structure can be related to the maximum response the structure, which can also be related to the cracks on the concrete. A distributed fiber optic sensor was developed to detect the cracks on the reinforced concrete structure under load. Fiber optic couples were used in the sensor system to extend the sensor system's capacity from one random point detection to more. An optical time domain reflectometer (OTDR) is employed for interrogation of the sensor signal. Fiber optic sensors are attached on the surface of the concrete by the epoxy glue. By choosing the strength of epoxy, the damage state of the concrete can be responded to the occurrence of the Fresnel scattering in the fiber optic sensor. Experiments involved monotonic loading to failure. Finally, the experimental results in terms of crack detection capability are presented and discussed.

A method to measure diffusion coefficient of transparent liquid solutions using digital holographic inteferometry is described. Holograms of a diffusively reflecting object through the experimental cell containing the diffusing solutions are recorded at different time instances. The recording medium is a CCD chip. The holographic interference of the object at two instances of time is numerically carried out in a PC and is used to determine the diffusion coefficient. Holographic interference fringes can be displayed on a PC monitor. The diffusion coefficients calculated using this method matched very well with literature values.

Pulsed laser system LASAG with maximal average power 150 W is used in our laboratory for experiments with various kinds of materials, process parameters optimisation for cutting, welding, drilling and surface treatment. Alignment of optical elements and good laser beam quality is critical parameter for successful result of laser treatment. Active medium - crystal in solid state laser is warmed up during laser action, because only some percent of input electrical power is turn to optical energy. Warm crystal has properties like a thick lens, which optical power is dependent on process parameters and kind of resonator. Also some defects in optical system - dirty or damaged mirrors or lens must be detect. Properties of non-visible near infrared beam can be tested by means of laser beam analyzer SPIRICON. In our system there are movable and changeable end mirrors and diaphragms to obtain five different types of resonators - basic one for welding and fibre applications and four ones for fine cutting and drilling. Measurements of beam profile for all these resonators were made with safety values of pulse length, energy and frequency. Control of losses in optical system was made to inspect quality of optical elements. Also measurement of laser beam outputting from three different fibre processing heads was realised. Control measurements on continual industrial Nd:YAG laser system were made. All data and capture pictures are stored and practical lessons for students in next school years were prepared.

In this paper, we present a modified transmission digital holographic microscope that can be used to image the state of polarization. The resulting device, called polarization digital holographic microscope (Pol-DHM), records in off-axis geometry the interference between two orthogonally polarized reference waves and the object wave transmitted by a microscopic sample and magnified by a microscope objective. A CCD camera records the resulting hologram. Using a single hologram, we reconstruct separately the amplitude and phase of two wave fronts, which are used to represent the object wave's state of polarization, represented by the azimuth and the phase difference associated to the polarization ellipse. The proposed method is illustrated with two applications. The first application is to use a 10-times magnification microscope objective to measure the birefringence induced by internal stresses in transparent materials such as a bended optical fiber. The second application is to use a 20-times microscope objective to image the state of polarization of a thin concrete sample and reveals birefringent properties of the different aggregates found in the concrete.

Plasma nitriding is an industrial surface hardening process which involves diffusion of nitrogen atoms into the metal surface to enhance material properties. The aim of this work is the development of a low cost device (based on a standard near infrared enhanced CCD camera) for the inline-characterization of such surface modifications during thermo-chemical heat treatment for improved process control. Due to relatively low process temperatures of about 400°C - 600°C the emitted light intensity of the heated metal parts is very weak. The imaging device therefore primarily utilizes the CCD-silicon’s spectral sensitivity for wavelengths around 1μm. As the emissivity of metals generally increases strongly at shorter wavelengths, the considered spectral range has certain advantages with regard to sensitivity for emissivity changes. Therefore, the measurement system is based on the principles of ratio pyrometry (dual-band-method), in which two images of the same scene, each taken at slightly different spectral bands, are used to determine the spectral light intensities. This results in an improved relative sensitivity for spectral changes (i.e. deviations from the gray-body hypothesis) which makes it possible to correlate the measured spectral intensities with surface modifications during the plasma nitriding process.

Based on the heterodyne interferometry and Fresnel equations, an alternative method for measuring the complex refractive index of a turbid medium. A light beam is incident on the boundary between a right-angle prism and a turbid medium. The phase difference between s- and p- polarizations of the reflected light occurs. The phase difference depends on then incident angle and the complex refractive index of a turbid medium; their relation can be derived from Fresnel equations. The phase difference can be measured accurately with the heterodyne interferometry. Because there are two unknown parameters to be estimated, at least the phase differences under two different conditions should be measured. Then, these measured data are substituted into the derived relation, and a set simultaneous equation is obtained. If the simultaneous equation is solved, the complex refractive index can be estimated. Because the reflected light from the boundary is measured, the scattering noises coming from the turbidity of the tested medium can be greatly reduced. In addition, this method has some merits such as simple optical setup, high sensitivity, high stability, and suitability for a little amount of the tested medium in its native state (without dilution).

With the ongoing reduction of structures sizes within electronic devices inspection tools have to be used allowing a resolution of below 50nm. This is not only necessary for a mere topological evaluation of materials or devices under test, but even more important for the nanoscopic determination of material parameters and device properties. When using waves as probes for this purpose, near-field techniques are quite often the only means for overcoming limitations in spatial resolution as due to Rayleigh's criterion, independently of the nature of the wave type used. In this manner acoustic and thermal waves can be applied for very high resolution testing as well as the well known scanning near-field optical microscope. Moreover, such techniques are not limited to simple systems in which the probing wave and the resulting interaction product are of same nature, but more complicated systems may be suitable to gain the information needed. In this manner near-field optical microscopy can be used for optical induced current measurements as well as for nanoscopic cathodoluminescence experiments. To achieve a comprehensive information on the sample, results gained with one special technique can be compared with others, such as scanning thermal or acoustic microscopy. These allow determination of mechanical and thermal properties with appropriate spatial resolution to be compared with , for instance, optoelectronic structures. The necessary instrumentation is described for such experiments with emphasis on the scanning near-field optical microscope. Examples for the application of near-field microscopies will be given for silicon technology, compound semiconductors, and ferroelectric ceramics.