This PDF file contains the front matter associated with SPIE Proceedings Volume 6995, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

When using the interferometric techniques, the optical path changes induce the wavefront deformations that in turn cause the appearance of fringes. One general characteristic of such an approach is the measurement sensitivity. The actual sensitivity of a holographic interferometer is a function of, on one hand, the parameters of the measuring system (such as the wavelength of the light used) and, on the other hand, the environmental conditions in which the measurements are being made. The later depend predominately on statistical fluctuations inherent to the particular laboratory conditions. In many applications the sensitivity is near the limits of the deformation detectability. In such cases, it is of vital interest to increase the number of interferometric fringes thus improving the quality of the acquired data. In this paper, we give an overview of the sensitivity increase through various experimental and numerical approaches. We also present a new numerical iterative method in which every cycle doubles the number of interferometric fringes. The method has shown to be especially useful in applications with sub-wavelength wavefront deformations.

We present dual-wavelength Digital Holographic Microscopy (DHM) measurements on a certified 8.9 nm high Chromium thin step sample and demonstrate sub-nanometer axial accuracy. We introduce a modified DHM Reference Calibrated Hologram (RCH) reconstruction algorithm taking into account amplitude contributions. By combining this with a temporal averaging procedure and a specific dual-wavelength DHM arrangement, it is shown that specimen topography can be measured with an accuracy, defined as the axial standard deviation, reduced to at least 0.9 nm. Indeed, it is reported that averaging each of the two wavefronts recorded with real-time dual-wavelength DHM can provide up to 30% spatial noise reduction for the given configuration, thanks to their non-correlated nature.

In digital holography, primary holographic fringes are recorded using a matricial CCD sensor. Because of the low spatial resolution of currently available CCD arrays, the angle between the reference and object beams must be limited to a few degrees. Namely, due to the digitization involved, the Shannon's criterion imposes that the Nyquist sampling frequency be at least twice the highest signal frequency. This means that, in the case of the recording of an interference fringe pattern by a CCD sensor, the inter-fringe distance must be larger than twice the pixel period. This in turn limits the angle between the object and the reference beams. If this angle, in a practical holographic interferometry measuring setup, cannot be limited to the required value, aliasing will occur in the reconstructed image. In this work, we demonstrate that the low spatial frequency metrology data could nevertheless be efficiently extracted by careful choice of twofold, and even threefold, undersampling of the object field. By combining the time-averaged recording with subtraction digital holography method, we present results for a loudspeaker membrane interferometric study obtained under strong aliasing conditions. High-contrast fringes, as a consequence of the vibration modes of the membrane, are obtained.

Resolution is an important issue in inspection of objects on microscopic scale. Various approaches have been investigated to increase the optical resolution behind the diffraction limit of an optical imaging system. Demonstration that super-resolution is possible have been also established in interference microscopy. We have studied the possibility to use diffraction gratings, in different experimental configurations for increasing the aperture of an optical imaging system. The aim of the study is to demonstrate that super-resolution is possible and is a practical and viable method for a coherent optical microscope. We take benefit of the numerical reconstruction properties of DH in combination with diffraction grating to get super-resolution. Various attempts have been performed and results are presented and discussed. The approaches could be used for metrology and imaging application in various fields of engineering and biology.

In Digital Holography (DH) the numerical reconstruction of the whole wavefront refracted or reflected by a sample object allows one to extract the wrapped phase map mod, 2π. In fact, since the hologram is coded numerically as a digitized image, both the wavefront amplitude and phase can be reconstructed simultaneously to provide amplitude and phase contrast imaging. The resolution in the image plane is the reconstruction pixel size that depends on wavelength, reconstruction distance and the size of the CCD recording area. Efforts to improve the resolution of DH reconstructions have been accomplished, following various strategies: increasing of the hologram aperture by moving the camera in different positions or even by using synthetic aperture approaches, using a diffraction grating to record digital holograms with a wider solid angle in the object beam, or using multiple sources and/or multiple acquisitions. Although all of these methods allow one to increase the spatial resolution, one more complication exists concerning the loss of resolution that occurs in the usual DH reconstruction approaches. It can occur that the reconstructed wrapped phase map in the image plane is undersampled because of the limited pixel size which limits the spatial bandwidth of the reconstructed image. In such a case the phase distribution cannot be retrieved correctly by the usual unwrapping procedures. We show that the use of the digital Lateral-Shearing Interferometry (LSI) approach in DH provides the correct reconstruction of the phase map in the image plane, even in extreme cases where the phase profile changes very rapidly. We demonstrate the effectiveness of the method in a particular case where the profile of a highly curved silicon micro-electromechanical system membrane has to be reconstructed.

Digital holographic microscopy permits quantitative phase contrast imaging of reflective and (partially) transparent samples. The utilization of low coherent light sources opens up prospects for a reduced phase noise by avoiding multiple reflections in the experimental setup. Thus, light emitting diodes (LEDs) have been investigated for applicability as low cost light sources in digital holographic microscopy. The LEDs were characterized for the spectral properties and the resulting coherence length. Furthermore, dispersion effects and their influences on the interferogram formation have been analyzed. Since the interference fringe number of off-axis holograms is limited by the coherence length of the LEDs (few micrometers) in addition to spatial phase shifting digital holographic reconstruction techniques, temporal phase shifting procedures were applied. The characterization of the lateral and axial resolution has been performed for both temporal and spatial phase shifting techniques by investigations on technical specimen. Finally, the application on biological samples is demonstrated by investigations on pancreas tumor cells.

In an adaptive measuring system the components of the optical arrangement may be changed automatically to adapt them to the conditions of the measurement. One mayor task of these systems is to perform automatic measurements even if the deformation is higher than the upper measuring range of the basic method. Also adaptive measuring system can help to understand what happened with the object due to the load. Digital holography and TV holography is the most promising tool for industrial applications. In our investigation adaptive methods and optical elements were developed and investigated for these techniques. Using these automatic evaluation procedures alternative output of the fringe system can be found.

Sensors based on materials with high refractive indices are desirable for sensing applications where a low penetration depth of the evanescent field into the covering analyte medium is required. To enhance the proportion of power carried into the covering medium while keeping the penetration depth low, a waveguiding device can be coated by a high-index film of metal oxide. We present numerical calculations as well as experimental comparisons between the evanescent fields of titanium dioxide-coated and uncoated waveguides in lithium niobate. The experiments were performed by using a Scanning Near-Field Optical Microscope (SNOM) in collection mode, which is an appropriate tool to measure and characterise evanescent fields. The coating of the waveguide leads to an enhancement of the power carried out into the covering medium by a factor 15 while the penetration depth remains the same in the range of a few 10 nm.

Integrated optic interferometric systems have been developed since many years and most of them are connected with telecommunication. In case of our group research profile we are focused on integrated optic sensors technology. One of possible application is the atomic force microscope (AFM). In the paper is presented the new concept that combines the AFM with the integrated optic interferometer. In the AFM system a cantilever movement control is the most important. The main goal of the project is improving sensitivity of the AFM by means integrated optic Michelson interferometer (IOMI). The optical waveguide structure was fabricated by surface micromachining technique, based on sandwiched silicon oxide and silicon oxynitride layers. The standard IOMI consist of two Y-junction in which one arm is playing the role of reference arm and other the measuring arm. Such configuration requires four fiber-to-chip connections. Thus, in our configuration, the integrated optic loop mirror in reference arm is fabricated. In the signal arm of our chip standard Grin lens to form an illumination cantilever optical beam is used. In the paper some theoretical descriptions and preliminary results are presented. The possibility of applying the heterodyned detection scheme in a IOMI as a step with sensitivity improvement is described, also. As the project is in progress, the paper is focused in the fabrication of the optical sensor. Next step will be optimization of the electronic part to improve the z-axis sensitivity of the AFM.

The Nanometer-Coordinate-Measuring-Machine (NCMM) has the ability to scan large areas at nanometer resolution for the purpose of quality assurance of nanostructured products. The device combines a conventional atomic force microscope (AFM) with a precise positioning system. By locating the AFM at a fixed point and moving the sample with the positioning system a scan range of 2.5 x 2.5 x 0.5 cm³ and a repeatability of 0.1 nm is achieved. Since all movements of the positioning system are measured via laser interferometers, the Abbe-principle is kept in every dimension, the use of materials with a low thermal expansion coefficient (like Zerodur and FeNi36) and an overall coordinate system the system provides unique measurement conditions (traceability to the meter definition; repeatable and fast scans of the region of interest). In the past the NCMM was used to make the first large area scan of a microelectronic sample. Our present work focuses on automating critical dimension measurement through the use of a-priori-knowledge of the sample and optical navigation. A-priori-knowledge can be generated by the use of CAD-Data of the sample or scans with white light interferometry. Another present objective is the optimization of the measurement parameters for specific sample topologies using simulation and also empirical methods like the Ziegler-Nichols method. The need of efficient data processing and handling is also part of our current research.

The progress of modern nanoelectronics, optoelectronics, nanophotonics, and microoptics is determined mainly by nanolithography advances. The electron beam lithography tools possessing a few nanometers resolution and good flexibility have a good outlook for creation of devices of this type. From the electron beam lithography tools only tools with sharp focused beam may be used for pattern generation over nanoscale area, but the writing speed thereof may decrease dramatically as the beam diameter d is reduced as d^--6 over this area. The theoretical analysis showed that the application of electron beam monochromator could not only improve resolution, but increase also the beam current over the minimum diameter area. Numerical modeling of heating process under scanning by electron beam is performed also to fit the electron lithography systems and scanning electron microscopy. Areas of safe work with sensitive to heating samples are determined. A conditions and prospects of development of the various electron beam lithography systems are considered. The achievements of electron beam lithography are compared with success in the field of other lithography techniques.

The subject of this paper is the use of aluminum nitride (AlN) as an actuation layer in MEMS/MOEMS systems. This material shows a good piezoelectric properties related to deposition conditions. AlN is a promising candidate for the acoustic wave devices, MEMS applications and sensors what have been already proposed. Up to now, AlN is still a technological challenge and many of its micromechanical and piezoelectric properties are not precisely described. That is why our study has been focused on the determination of the material parameters like Young's modulus, residual thin film stress, piezoelectric coefficient d₃₁ and mechanical behaviour of especially designed cantilevers. To ensure the optimum design, functionality and reliability of those actuators the theoretical solution and the numerical simulations of mechanical performance by the Finite Element Method (FEM) were performed. The created model of device takes into account multiple film stacking. For the characterization it was chosen a full-field optical technique applied in a multifunctional interferometric platform. Proposed set-up performs the measurement in static and dynamic regimes with nanometer sensitivity and high spatial resolution. The hybrid method of analysis combining the experimental and numerical results has been used to better understand the properties of these microdevices, facilitate their designing and to optimize their technological process. The optimum goal is a developing of the high quality and reliable AlN-driven cantilevers for use in MEMS/MOEMS.

In this paper vibration characterization of MEMS cantilevers are presented using lens-less in-line digital holographic microscope (LDHM). In-line digital holography provides larger information capability with higher phase sensitivity, and full CCD sensor area is utilized for real image reconstruction. In lensless in-line digital holographic microscope, a highly diverging beam replaces the conventional microscope objectives to provide the required magnification. The diverging wave geometry also reduces the effect of twin-image wave caused by the in-line holographic geometry. For vibration analysis, the time averaged holograms were recorded corresponding to different vibration states of the cantilevers. Direct numerical evaluation of the amplitude and phase information from single time averaged hologram provides the full-field real time quantitative analysis. The experimental study of vibration measurements of Aluminum nitride (AlN) driven cantilevers is performed. The full field study shows the simultaneous vibration behavior of many cantilevers corresponding to same input conditions. Our study shows the shift in the resonant condition of cantilevers both for first and second resonant frequencies. This kind of analysis is most suitable to optimize and monitoring the fabrication process of cantilevers.

Novel modifications of an environmental scanning electron microscope (ESEM) were made in order to measure the local deformations in drying cement paste. These nondestructively determined moisture-induced plane strains, obtained in 1 mm thick cement paste samples, are orthotropic. They vary with variations of relative humidity between 70%-80% and 40%-50%, being the highest at 20% RH. Both drying shrinkage and expansion of cement paste microstructure occur in early-age and mature samples. Microcracking due to moisture gradient could not be avoided, although very thin samples were examined with gradual reduction of relative humidity in drying steps of 10%. The coefficient of deformation of cement paste is directly proportional to shrinkage/expansion. It depends on variations of relative humidity during drying in ESEM and the sample age.

Interferometry is a powerful and versatile tool for active MEMS characterisation. The high accuracy measurement of deformations and vibrations of MEMS structures is an important application and well described by classical interferometry. Deformation measurements in multi-layered structures requires a more sophisticated approach. All phase changes along the optical path of the object light influence the measurements. Thus the shape and the displacement of obstacles (like glass cover plates) must be included to quantify the measurement results. The paper presents numerical simulations of the light path in an interferometric deformation measurement. A ray tracing program is developed that keeps track of the optical path length and can thus be used to analyse disturbances along the optical path. The simulations show how the deformation of more than one interface influences the phase measurement. The phase errors are quantified and the reliability of the deformation measurements is evaluated. Different interface geometries are examined. The simulations are compared to measurements on a MEMS pressure sensor.

Micro-technology plays an important role in everyday life, without being much perceived. Cell phones, for instance, are daily equipped with small electronic components, which must have their quality level assured. New micro-metrology techniques were developed in the last years for such purposes. They are usually only suited for measuring specific and individual object properties (e.g. geometry, roughness, contours). A multi-sensorial approach is needed to improve the inspection range and flexibility of a micro-production cell, so that the distinct features of different industrial parts may be inspected intelligently and independently of their surface properties. This work provides a basic review on some of the most important "non-contact" micro-metrology techniques (optical and non-optical), performing a comparison of these methods among their distinct capabilities and possible industrial applications/integration scenarios. Based on the already existent sensor fusion principles, the MEOND concept will be introduced to build up flexible inspection systems for small series production by combining sensors and data, focusing possible application scenarios of the micro-world. The fusion of micro-metrology techniques has not yet been far explored and is extremely important to assure flexibility, autonomy, accuracy and robustness for the assembly of MEMS/MOEMS systems.

Today there exist different commercial micro-optics measurement instruments for the characterization of micro-optical components and microlenses in particular. However there is often a lack of a complete quantitative optical characterization of the latter components. Therefore we will focus in this paper on the optical characterization of all types of refractive microlenses, more in particular spherical and aspherical microlenses. Moreover the results of the performed round robin within the European 6th FP Network of Excellence on Micro-optics "NEMO" will allow us to select the most appropriate instrumentation tools for characterizing refractive microlenses.

Cartilage degenerative diseases like osteoarthritis affect the organization of the biological extracellular matrix (ECM) surrounding chondrocytes. This ECM is mainly composed by collagen giving rise to a strong Second Harmonic Generation (SHG) Signal, due to its high non linear susceptibility. Mechanical stress leads to perturbation of the collagen network comparable to modification occurring in disease. To be sure that SHG signal comes specifically from the collagen network, the enzymatical action of Collagenase was followed. We clearly noted the decrease of the collagen specific signal according to incubation time due to enzymatic degradation. To characterize structural modification on the arrangement of collagen fibers in the ECM, we used image analysis based on co-occurrence matrix (Haralick). Textural features give information like homogeneity ('Angular Second Moment') or size of textural elements ('Inverse Difference Moment', 'Correlation'). Samples submitted to compression are characterized by higher 'Correlation', associated with a decrease of 'IDM' and 'ASM'. Those evolutions suggest the presence of long linear structures, an effect of packing of collagen fibrils and the apparition of nodes where the density of collagen is important versus areas showing a lack of molecules. Collagen I, II and VI are biomarkers characterising disease states since its presence is increased in pathological cartilage (osteoarthritis). Fluorescence Lifetime Imaging Microscopy (FLIM) associated to Spectral and SHG analysis confirmed the presence of Collagen I and II in the extracellular and Collagen VI in the pericellular matrix of chondrocytes. SHG, FLIM and Spectral Imaging combined with multiphoton excitation enable tissue imaging at deep penetration. We pointed out a local modification of the ECM of cartilage without any labelling (SHG) under mechanical stress. Thus the association of all these techniques represents a potential diagnosis tool for disorganization of collagen.

Micro-optical components are of growing interest and used in very different applications such as displays, biophotonics, optical-data communication... More in particular, refractive microlenses and refractive microlens arrays are widely used. The fabrication of these components has been extensively investigated and today different technologies are already commercially available such as thermal reflow, laser ablation, reactive ion etching, microject printing... These technologies allow the fabrication of high-quality microlenses in different materials, however these fabrication methods are often too expensive and too time-consuming for prototyping. In our facilities, we implemented Deep Proton Writing (DPW) as a rapid prototyping technology to fabricate plastic refractive microlenses and microlens arrays. To reduce the calibration time and minimize the influence of uncontrollable external parameters we built a transmission Mach-Zehnder interferometer allowing to monitor in situ and in real-time the growing of the refractive microlenses. This means that we can stop the growing process of the microlenses as soon as the predefined specifications are reached. Additionally we can determine out of this interferometric data the geometrical properties and optical quality of each of the microlenses. We have studied the precision and accuracy of our interferometer for the characterization of the latter components. In this paper, we will present the latest results showing the performance of our set-up and the resulting enhancements of our technology.

We present in recent work release of very precise length standard based on laser frequency comb. Each frequency comb produces a frequency spectrum with equidistant modes f_rep with frequency offset f_ceo. Stabilized frequency comb produce a very precise frequency rule. Fabry-Perot cavity is frequently used as interferometer using a scanning mirror position. Depending on mirror coatings and reflectivity of mirrors one could obtain a spectrum of any laser adjusted to the Fabry-Perot cavity. Two methods of length stabilization using the Fabry-Perot cavity are presented and compared. One method uses the cavity of mirror distance defined by ν_cav as an integer multiple of f_rep. The second is based on selection of narrow part of the spectrum and very wide inter-mode frequency ν_cav. Two continuous working He-Ne stabilized lasers for coarse Fabry-Perot mirror spacing length adjustment were separated by different optical polarization and one stabilized frequency comb separated from both lasers operated at different central wavelength.

The single point Optical Diffraction Strain Sensor has been extended to a patent-pending Multipoint Diffraction Strain Sensor (MDSS) using a microlens array. The system was further extended for strain measurement with variable sensitivity and measurement range. In this paper, the MDSS is shown to measure both tilt and non-uniform strain with a sensitivity of 0.41 mε/pixel and 4.7 mrad/pixel respectively. As validation the strain measured by the MDSS is compared with that by a micro-moiré interferometer with a Gabor filtering method for fringe pattern analysis, while the tilt is compared with derivatives of the surface profile measured by a confocal microscope.

We present results of measurement of purity of a set of iodine cells made at our institute. The purity was tested by improved method based on measurement of induced fluorescence and evaluation by the Stern-Volmer formula. The reproducibility of the fluorescence detection system was improved by introducing of additional compensation for the pumping laser spectral and power instabilities. Frequency-doubled Nd:YAG lasers stabilized with these cells were compared to evaluate their frequency shifts. The absolute frequencies of selected iodine hyperfine transitions were measured in direct laser frequency comparison with the reproducibility well below the kHz level. The results indicating the iodine cell purity are presented with relation to the absolute frequency shifts. This not only highlights the influence of iodine cell quality onto the stability and absolute frequency of laser etalons but also shows the way towards improvements of the iodine cell manufacturing technology.

Pupil-Plane Scanning White-Light Interferometry measures reflectivity as a function of angle of incidence, wavelength and polarization in one location of an object surface. This information is converted into ellipsometric information and allows the characterization of material optical properties and layer thickness in the case of layered structures. We illustrate the capability of the method by measuring the thickness and refractive index of thin film standards. The information is also used to create accurate 3D topography maps of complex object structures.

Fringe projection is a commonly used method for 3D surface metrology. Numerous applications have demonstrated a measurement field from a few millimeters to several meters. To enable the measurement of micro systems with this method, a zoom stereo microscope from Leica was used as the basis for the implementation of a fringe projection microscope. A state of the art twisted nematic WUXGA LCD was used for flexible fringe generation. The high fill factor of this reflective LCoS in combination with a 500 Lumen LED and a 12 bit CCD camera delivers fringe patterns with high contrast. This allows us to measure objects with both a strong reflectivity variation and a low reflectivity. The second main objective was to increase the measurement field and the depth of field. Using the zoom system and exchangeable microscope objectives, the measurement fields could be changed quickly from 4 cm² to less than 1 mm². Depending on the measurement field, the depth of field was between 5.22 mm and 0.018 mm. However, this was often not sufficient to measure the complete depth of a 3D-object. The microscope system also features an integrated high precision motor stage, which is already used for system calibration. Based on this, we implemented a new z-stitching method where n measurements at different well determined z-positions of the motor stage were performed. The n resulting topography maps can be stitched together to get the complete depth map of the entire object. Thus the depth measurement range is only limited by the mechanics of the z-stage.

Within the last years, interest in photonic wires and photonic crystals grew due to their demonstrated ability of controlling light propagation and characteristics. One of the limitations of such devices is due to the induced roughness during the fabrication process. Generally, an increase in roughness leads to loss increase thus limiting the propagation length and postponing the commercialization of such structures. In this paper we present a new algorithm for measuring the sidewall roughness of our devices based on atomic force microscope (AFM) approach. Using this algorithm, the roughness can be quantified and thus actions in decreasing it can be taken improving the device's performance.

The solution of the inverse problem in scatterometry, i.e. the determination of periodic surface structures from light diffraction patterns, is incomplete without knowledge of the uncertainties associated with the reconstructed surface parameters. With decreasing feature sizes of lithography masks, increasing demands on metrology techniques arise. Scatterometry as a non-imaging indirect optical method is applied to periodic line-space structures in order to determine geometric parameters like side-wall angles, heights, top and bottom widths and to evaluate the quality of the manufacturing process. The numerical simulation of the diffraction process is based on the finite element solution of the Helmholtz equation. The inverse problem seeks to reconstruct the grating geometry from measured diffraction patterns. Restricting the class of gratings and the set of measurements, this inverse problem can be reformulated as a non-linear operator equation in Euclidean spaces. The operator maps the grating parameters to the efficiencies of diffracted plane wave modes. We employ a Gauss-Newton type iterative method to solve this operator equation and end up minimizing the deviation of the measured efficiency or phase shift values from the simulated ones. The reconstruction properties and the convergence of the algorithm, however, is controlled by the local conditioning of the non-linear mapping and the uncertainties of the measured efficiencies or phase shifts. In particular, the uncertainties of the reconstructed geometric parameters essentially depend on the uncertainties of the input data and can be estimated by various methods. We compare the results obtained from a Monte Carlo procedure to the estimations gained from the approximative covariance matrix of the profile parameters close to the optimal solution and apply them to EUV masks illuminated by plane waves with wavelengths in the range of 13 nm.

Optical phase conjugation designates the "reflection" of a ray of light back into the direction from where it came. This physical effect can be realized by sophisticated non-linear optical devices. Examples are phase conjugating mirrors based on stimulated Brillouin scattering. Phase-conjugated mirrors are advantageous in instrument design, because they can make an optical instrument less sensitive to misalignments or a laser resonator less sensitive to optical aberrations caused by a phase distorting medium. As quasi-phase-conjugated devices we might designate devices that show this special feature in an approximated way. They can be realized with less technical and scientific effort and still offer an improvement in system stability and instrument insensitivity. An established way to make quasi-phase-conjugated devices is by implementing arrays that are made up of tiny retro-reflectors. These retro-reflectors may be realized using micro-lenses or tiny corner cube reflectors. Quasi-phase-conjugated arrays have applications in optical sensors and instruments as well as in illumination technology. Such retrodirective arrays are analyzed from the point of view of the sensitivity of their retro-reflective properties. Emphasis is put on considerations of geometrical device tailoring, namely on the question how the geometry of a unit cell that is repeated in the array arrangement influences the retro-reflection properties of the optical arrangement. A parameter study is provided that is targeting at robust retrodirective arrangements.

A growing trend in architecture and design is the use of steel. For those applications the visual appearance of the surface is of primordial importance. In this research we model the reflection of light on a rough steel surface, coated with a transparent polymer layer. A number of optical non-destructive techniques were used to determine the roughness (AFM, white light scattering interferometry) and optical constants (spectroscopic ellipsometry) of the samples. AFM measurements were used to determine whether this polymer layer followed the roughness of the substrate or had a roughness all of its own. Using the Modeled Integrated Scattering Tool (MIST) developed by the National Institute of Standards and Technology (NIST) we were able to calculate the reflection of these surfaces and compare them to experimental reflections measured by scatterometry.

A Low Birefringence Polariscope (LBP) is developed to provide high-resolution, full-field thickness measurement of the liquid crystal cell. By rotating the analyzer, phase shift images can be captured and analyzed to obtain the gap thickness and uniformity of the liquid crystal cells. A comparative study with the commercial system shows good agreement. The proposed method yields accurate and repeatable full-field measurement of the LC cell with a simple experimental setup.

In Fourier modal methods like the RCWA and the Differential Method the Li-rules for products in truncated Fourier space have to be obeyed in order to achieve good convergence of the results with respect to the mode number. The Lirules have to be applied differently for parts of the field that are tangential and orthogonal to material boundaries. This is achieved in the Differential Method by including a field of vectors in the calculation that are normal to the material boundaries. The same can be done laterally in each layer of an RCWA calculation of a 2-D periodic structure. It turns out that discontinuities in the normal vector field can disturb the computation especially when metallic materials are dominant in the structure which would make the usefulness of the normal vector method questionable. So it is of great importance to investigate how normal vector fields can be established with as few discontinuities as possible. We present various methods for the 2-D RCWA and the 1-D and 2-D Differential Method and compare the respective convergence behaviors. Especially we emphasize methods that are automatic and require as few user input as possible.

We present a new method of phase retrieval from the spectral interferograms, which is based on the use of a windowed Fourier transform applied in the wavelength domain. First, the numerical simulations are performed to demonstrate high precision of the phase retrieval from the spectral data related to a slightly dispersive Michelson interferometer comprising a thin-film structure. Second, the feasibility of the method is confirmed in processing experimental data from the Michelson interferometer with SiO₂ thin film on a silicon wafer to determine precisely the thin-film thickness. We confirm very good agreement with the previous results obtained by the fitting of the recorded spectral interferograms to the theoretical ones. Finally, the method is used in processing experimental data from the Michelson interferometer with two metallic mirrors. From the retrieved phase function, the effective thickness of the beamsplitter made of BK7 glass is determined precisely.

In this paper, we present a phase retrieval method where a sequence of diffraction speckle intensities, recorded by tuning the illumination wavelength, is used. These recordings, combined with an iterative calculation method, allow the reconstruction of the amplitude and the phase of the wavefront. The main advantages of this method are: simple optical setup and high immunity to noise and environmental disturbance, since no reference beam or additional moving parts are needed. Furthermore, this method allows for an extended wrap-free phase measurement range by using synthetic wavelengths. The technique shows great potential in some fields of micro-metrology, such as lensless phase contrast imaging and wavefront sensing.

This paper proposes a Fourier-Optics-based non-invasive quality assessment tool for a micron-thick bar. Our design concept relies on a transmissive optical architecture to reduce the effect of an object's angle misalignment that can introduce a significant measurement error. From the far-field diffraction pattern of the micron-thick bar, we determine its thickness from the distance either between the two adjacent diffracted order beams or between a high order diffracted beam and the zero order beam. In addition, because all diffracted order beams are aligned, we use the resulting slope to determine the edge parallelism. The amount of edge defect on the sample can be investigated by evaluating the distribution of the optical intensity inside diffracted order beams. Our theoretical analysis indicates that for a 238-μm thick bar, our proposed concept provides better than 1 μm and 0.1° resolutions in thickness and edge parallelism measurements. Our experiment using a 635-nm wavelength laser diode and 22 sample bars with an average thickness of 238-μm shows that our approach can simultaneously evaluate the thickness and the edge parallelism of the bar samples as well as distinguish nicely edged bars from poorly edged bars. Key features include low cost, ease of implementation, robustness, and low component counts.

Aspheric lenses are of increasing importance in compact imaging systems. New developments in production technologies have led to the so called wafer level production with several thousands of lenses on a single wafer. This high volume production demands fast testing equipment which allows for the characterization of complete imaging systems as well as of all of its single components. In most of the cases conventional methods cannot be used to measure single lenses or objectives in earlier production states. Although e.g. the measurement of the modulation transfer function is a well established method for fast and accurate quality inspection of entire objectives it has its limitation for single lenses. Due to its very large dynamic range the Shack-Hartmann sensor is able to measure a very broad range of spherical and aspherical lenses as well as partially or fully assembled objectives. With the combination of a fast high accuracy wavefront sensor and special positioning algorithms which allow for high throughput in mass production a new flexible instrument has been developed.

When a signal is sampled at a rate less than twice its maximum frequency aliasing is occurred, which causing lower frequencies to appear in the sampled signal. In displaying an image on a monitor we also performing a kind of sampling. Displaying a sinusoidal image, with a frequency that is approximately an integer multiple of pixel frequency of the monitor, generates a frequency that is very smaller than the frequency of presented image that appears as a moire fringe. Characteristics of this fringe depend on the pixel size of the monitor and the frequency of the displayed image. By changing the image frequency one can access a moire fringe of infinite period. In this case there is a simple relation between the image period and the pixel period of the monitor. Thus by knowing the period of the presented image, the period of the pixels can be obtained using this relation. The error in determining the number of the pixels of a monitor is estimated to be less than one pixel.

We present a numerical technique for refocusing and three-dimensional localization of micron-size particles observed in a digital holographic microscope working in transmission. We use Fourier method for the extraction of complex amplitude from the single exposition digital holograms. The three dimensional localization of objects is performed using the focus plane determination method based on the integrated amplitude modulus. We apply the refocusing criterion locally for each pixel, using small overlapping windows, in order to obtain a synthetic image in which all objects are refocused independent from their refocusing distance. We perform image segmentation and object detection using both the synthetic refocused image and the value of refocusing criterion, which allows us to obtain a high detection efficiency with very low number of false detections. While the lateral precision of localization is determined by the optical resolution of the setup, the vertical accuracy depends on the parameters of the digital holographic reconstruction. We improve the accuracy of vertical localization using an additional refining procedure in which each particle is treated separately. We analyze the robustness and accuracy of our approach and present its successful implementation in particle flow experiments.

The structure and optical properties of the heterostructures, which contain an ultra-thin InGaN layers with GaN or AlGaN barriers, grown by MOCVD method were investigated by photoluminescence and high resolution X-ray diffraction (HRXRD) tehnigue. The exciton localization energy, Urbah energy and charge carries activation energies were obtained from analysis of the temperature dependences of the photoluminescence spectra for the In-rich areas (QDs). In these structures the In-rich areas are shown to appear in ultrathin InGaN layers due to phase decomposition. That leads to exciton and carrier localization in fluctuation minima, which prevents them from tranport to nonradiative recombination centres. The indium composition in the InGaN QDs were obtained using theoretical model, which describes the electron transition energy as a function of In-rich areas parameters. The parameters such as deformation of InGaN/GaN region and layer thickness were determined from HRXRD. The suggested approach is supposed to be effective method for analysis of the optical properties of InGaN/GaN heterostructures.

Nanoindentation testing has proved to be an effective tool to determine the mechanical properties of small volumes of materials applied in various micro-systems, including hardness, indentation modulus, creep and so on. Nowadays, with the help of advanced numerical methods, especially the finite element analysis (FEA) technique, further mechanical properties of the material under test (e.g. tensile strength, etc.) can be interpreted from the typical indentation curve. However, the reliability and accuracy of these analytical models have to be well tested. Recently, the deformed topography of the interlayer surface within the tip-film-substrate system has been proposed to be the reference for the evaluation of FEA and other mathematic models for indentation testing. Here an in-situ interlayer deformation imaging system based on differential confocal microscopy is therefore developed, which has the capability to measure in-situ the real-time topography deformation within a layered specimen during nanoindentation testing. By means of linear regression and interpolation of the linear region of the standard confocal microscopy, differential confocal microscopy (DCM) can achieve a very high resolution for topography measurements. However, the actual capability and measurement uncertainty of DCM would be subject to those common-mode error sources like surface heterogeneity, intensity fluctuation of the light source, etc. In this paper an improved DCM is proposed, which introduces an additional point detector to the conventional DCM, creating dual confocal signals with slight relative axial shifting. The real topography of the surface under test can then be easily deconvoluted from the dual differential signals, whilst the common-mode errors within the measurement are eliminated. A prototype was developed and applied for measuring a step-height composed of two different materials and for in-situ inspection of the interlayer deformation during nanoindentation testing. Preliminary experimental results verify the feasibility and accuracy of the proposed method.

In this paper we present optical phase-conjugation based on the degenerate four-wave mixing (DFWM) arrangement in photorefractive crystal. The 532nm beam from a low-power Nd:Yag laser was split to form two counter-propagating pump beams and one probe beam in the DFWM geometry. Experiments were carried out by varying the parameters (angle of separation between the forward-pump and the probe beam, writing beam intensities) that influence the phase-conjugate beam reflectivity. High reflectivity optical phase-conjugation is hereby reported for low-power lasers. The dependence of phase conjugate reflectivity on signal to pump ratio (m) and forward to backward pump ratio (q) have been investigated experimentally