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.