In this paper we present a method for tomographic imaging using multiple wavelengths in digital holographic microscopy. This method is based on the recording at different wavelengths equally separated in the k-domain, in off-axis geometry, of the interference between a reference wave and an object wave reflected by a microscopic sample and magnified by a microscope objective. A couple charged device (CCD) camera records consecutively the resulting holograms, which are then numerically reconstructed to obtain their resulting wavefront. Those wavefronts are then summed. The result of this operation is a constructive addition of complex waves in the selected plane and destructive addition in the others. Varying the plane of interest enables the scan the object in depth. For the presented simulations and experiments, twenty wavelengths are used in the 480-700 nm range. An object consisting of irregularly stairs with heights of 375, 525, 975, 1200 and 1275 nm is reconstructed. Its lateral dimensions are 250 × 250 microns. The results show clearly a 3D imaging technique with axial resolution under the micron.

In this paper in-line digital holography has been explored for dynamic micro metrological applications. In in-line digital holography, full CCD sensor area is utilized for real image reconstruction of the objects with less speckle noise. Numerical evaluation of the amplitude and phase information during reconstruction process finds promising applications in optical micro-metrology. Vibration analysis of the smaller object has been performed by combining the time average principle with in-line digital holographic methods. A double exposure method has been explored for measurements, which is simultaneously used to suppress the overlapping of zero-order and twin image wave with real image wave. The vibration amplitude and mean static state deformation of the harmonically excited object are analysed separately from time average in-line digital holograms. The experimental results are presented for a thin aluminium membrane of 5mm diameter.

This paper presents Digital Holographic Microscopy (DHM) quantitative measurements of transparent high aspect-ratio microstructures. Our experiment was performed using a digital holographic microscope in transmission configuration with a 60x magnification 1.3 NA oil immersion microscope objective, with a diode laser source at 664 nm. We used a calculation model based on the use of two immersion liquids for the experiment, the first one to resolve the phase jumps by using a refractive index liquid close to the sample index, in combination with a second one to retrieve the sample topology from the optical path length information. Such a model makes absolute topographic measurements of high aspect ratio transparent samples achievable by DHM. The model is then applied to measure 25 and 50 m transparent micro-corner cubes arrays, which exhibit up to 1:1,4 aspect ratio with theoretical slopes up to about 55 degrees. Thanks to our phase measurement precision down to 1°, we found possible to measure accurately the slopes of each face of the microstructures under investigation, and this with a good theoretical agreement.

Digital Holographic Microscopy (DHM) is a powerful imaging technique allowing, from a single amplitude image acquisition (hologram), the reconstruction of the entire complex wave front (amplitude and phase), reflected by or transmitted through an object. Because holography is an interferometric technique, the reconstructed phase leads to a sub-wavelength axial accuracy (below λ/100). Nevertheless, this accuracy is difficult to obtain from a single hologram. Indeed, the reconstruction process consisting to process the hologram with a digital reference wave (similar to classical holographic reconstruction) seems to need a-priori knowledge about the physical values of the setup. Furthermore, the introduction of a microscope objective (MO), used to improve the lateral resolution, introduces a wave front curvature in the object wave front. Finally, the optics of the set-up can introduce different aberrations that decrease the quality and the accuracy of the phase images. We propose here an automatic procedure allowing the adjustment of the physical values and the compensation for the phase aberrations. The method is based on the extraction of reconstructed phase values, along line profiles, located on or around the sample, in assumed to be flat area, and which serve as reference surfaces. The phase reconstruction parameters are then automatically adjusted by applying curve-fitting procedures on the extracted phase profiles. An example of a mirror and a USAF test target recorded with high order aberrations (introduced by a thick tilted plate placed in the set-up) shows that our procedure reduces the phase standard deviation from 45 degrees to 5 degrees.

Digital holography (DH) and digital holographic interferometry (DHI) are very useful, robust, full-field visualization and measurement techniques applied for small objects, especially in the field of bioengineering and microelements system testing. Nowadays CCD/CMOS detectors and microlasers allow to build miniaturized and compact digital holographic head. Various approaches to develop DH/DHI systems including a variety of optical and mechanical solutions have been made. The main recent requirements for holocamera design include compactness, insensitivity to vibrations environmental changes and with good quality of output data. Other requirement is the ability to build a low-cost and robust system for sensing applications. In our paper, we propose a design of miniaturized holo-camera head with fibre optics light delivery system and remote data read-out. The opto-mechanical architecture allows out-of-plane and shape measurements of diffuse and reflective surfaces. The possible data capture schemes and software for enhanced quality numerical reconstruction of complex objects are discussed and the optimized methodology is determined. Also real-time optoelectronic hologram reconstruction is demonstrated on the base of remote data delivery to liquid crystal on silicon spatial light modulator. The performance of the system is tested on the resolution amplitude test and master sphere, while engineering objects in the experiments are static and dynamic microelements.

On the basis of the mechanically scratching using the Atomic Force Microscope, this paper proposes a new method for manufacturing high frequency grating. The grating was fabricated on a polycarbonate compact disc with a silicon AFM tip under the contact mode. The fabrication technique and the optimization of parameters for the technique are discussed in detail. From the experiment, the minimum spacing of the grating can reach 30 nm. The digital nano-moire patterns verify that the grating has good potential to be applied to the nano-deformation measurement.

The method presented here is an optical technique allowing the high productivity printing of long submicron period gratings by means of a phase mask illuminated by an intensity modulated laser beam. The continuous writing of the grating permits to avoid stitching errors and the fabrication of very long gratings. The main applications concern the fabrication of long optical scales for high resolution optical encoders. The experimental results presented here show 100 mm long resist gratings with 500 nm period.

Organic materials are taking a growing place in the development of new materials for data technologies thanks to the potential of molecular engineering, the flexibility of available chemical compositions, the low costs..., but also because of their unique optical and mechanical properties. In this context, photopolymers present specific advantages particularly interesting for high density optical data storage, based on the possibility of structuring their linear and nonlinear optical properties with a great facility by direct optical patterning. In order to understand and control the physico-chemical aspects of the photopatterning, means of investigation at a micro and nanoscopic scales are required. Not only the 3D imaging of the object is needed, but some structural information on the material is necessary to go further in the investigation of the involved phenomena. AFM used in Pulsed Force Mode (PFM) fulfils these requirements: the PFM mode is a non-resonant mode designed to allow approach curves to be acquired along the scanning path. It thereby provides a recording of the sample topography and extends the possibilities of the prevalent contact and intermittent-contact AFM modes to a direct and simple local characterization of adhesion and stiffness. This paper describes the principle of Pulsed Force Mode AFM and illustrates its usefulness for investigating of the photostructuration of polymer matrixes. In a first part, homogeneously irradiated films were characterized in order to demonstrate the sensibility of the PFM analysis. In particular, the PFM signal is correlated to the monomer conversion ratio that was measured by FTIR spectroscopy. In a second step, we illustrate the potential of PFM for the investigation of photopatterned films. Holographic gratings were recorded in an acrylate-based formulation and characterized by PFM. We have successfully assigned the different areas of the film that correspond to different incident intensities. Using the information recorded on homogeneous films, it is possible to obtain an estimation of the conversion of the monomer at sub-micronic scale. Such a study is of primary importance in order to understand the mechanism leading to microstructuration and thus to optimize this process in terms of resolution.

Photonic crystals are attractive optical materials for controlling and manipulating light. They are of great interest for both fundamental and applied research, and are expected to find commercial applications soon. In this work digital holography, white light interferometry and atomic force microscopy have been applied to the inspection and characterization of 1D and 2D nanofabricated LiN photonic crystals. Periodic pattern with periods ranging form several microns to a fraction of micron have been accurately analysed. Optical methods allow exploring relatively large areas while atomic force microscopy is well suited for high-resolution inspection of the small features.

The study of nanometre surface metrology is becoming more and more commonplace in industrial and research environments. Because of this expansion there are more and more technologies available for looking at the surface and due to the differences in the techniques each has its own specialist applications. Stylus profilometry, white light interferometry and confocal microscopy are common techniques used to measure surface metrology to nanometre precision. Strengths and weaknesses of each of the techniques are discussed with examples.

The paper provides new insights into Silicon wafer measurements in context of technological problems of developing a sophisticated measurement technique, which harnesses helium atom beam as a probe. Nano-resolution imaging techniques such as scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) are well-know in surface science. A scanning helium atom microscope, where a focused beam of low energy, neutral helium atoms is used as an imaging probe is a new concept creating non-destructive and non-invasive surface investigation tool in science and industry. This paper is focused on measurements of flatness and thickness of the wafer, which is used as a deflecting mirror of the helium beam. Two -optics based- measurement techniques are presented: scanning confocal system and the Fizeau interferometer. The latter is applied as a quick reference device placed close to the production line whereas the former offers high accuracy flatness and thickness maps of the wafers.

Topography measurements of MEMS devices are one of the helpful approaches for MEMS devices' quality control, performance evaluation, design optimization, etc. In order to fulfill the requirement to determine the surface topography of a MEMS actuator, especially those of comb-drive types, in which the surface under test is in general discontinuous, a novel principle of an optical differential probe is proposed, in which a common-path laser interferometer and a confocal position sensor are integrated. Details of design and development of the novel differential probe are discussed, including the influence of the geometrical dimensions of the microstructure under test onto the measurement results, basic criteria for the design of the afocal subsystem and edge determination with confocal microscopy. Experimental results verify that the proposed novel approach is applicable.

White light interferometry is a promising tool for industrial quality inspection. Since modern cameras offer a frame rate far above video-rate, the speed of these systems could be increased in order to fulfill the strong temporal constraints of inline inspection, i.e. the monitoring of every single part during the production process in just a few seconds. Its accuracy up to the sub-μm range enables even the detection of smallest defects like holes with a diameter of only a few microns and thus ensures a fast, contactless and high precision quality inspection. Due to the replacement of the mechanical phase shifting by a spatial phase shift, the commonly known white light interferometers could be extended to a one-shot line-profiling sensor. The main benefit of such a line-profiling technique is that also critical surfaces are accessible that deviate strongly from a plane shape, like rotary welds on cylindrical parts. It can be shown that the accuracy of the proposed system is comparable to the accuracy of conventional white light interferometers even on rough surfaces. Other parameters like lateral resolution and measuring range strongly depend on the optical setup and will be discussed in the following sections.

The paper concentrates on the double-refracting systems - particularly variable wavelength techniques (VAWI) for reflected light... The family of techniques for (transmitted and reflected light) is especially recommended for studying objects, which produce optical path difference more than a few wavelengths. In such cases classical approach consisting in measuring deflection of interference fringes is not useful because of edge effects that break continuity of interference fringes. The VAWI methods have been invented in the time when image processing devices and computers were hardly available. Automated devices unfold a completely new approach to the classical measurement procedures. The paper discusses mainly construction aspects of the systems in context of the computerised instruments.

In the paper we present method for three-dimensional measurement of birefringence distribution in anisotropic objects. The tool, which we used is combination of classic polariscopy with tomographic reconstruction method. Tomographic reconstruction is performed using the filtered backpojection algorithm. The results of measurement of glass capillary infilled with licquid crystal are presented together with the results of numerical simulation of measurement process. Simulations include polarized light propagation performed by means of finite difference time domain method combined with Jones calculus. The numerical simulations are performed for various birefringence values and allow for determination of relative errors of birefringence distribution. Additionally the absolute refractive indices are determined experimentally through the measurement of capillary with polarization sensitive microinterferometric tomography.

In Optical Diffraction Tomography (ODT) the refractive index is reconstructed from images with different illuminating wavefronts. In most cases the Born approximation is assumed, although this limits the applicability of the technique to weak-scattering problems. In this work we examine the scattering problem from first principles beginning from the Helmholtz equation that governs scalar diffraction and wave propagation. We demonstrate the use of the Born approximation and show typical errors when it is applied in practice. Solution of the Helmholtz equation using a Finite Element Method (FEM) with an appropriate Absorbing Boundary Condition (ABC) is described, and a non-linear optimization technique, the Conjugate Gradient Method (CGM), previously proposed for microwave imaging, is applied to the inverse problem.

In this paper we present the novel concept of tomography system for characterization of small phase microelements such as telecom fiber splices. We demonstrate the measurement method, existing setup and its modification towards creation of miniaturized waveguide based Mach-Zehnder interferometer for telecom fiber assessment. Additionally we present and analyze Deep Proton Writing as a promising technology for rapid prototyping of monolithic microinterferometer in PMMA.

In the paper the experimental and numerical reconstruction of phase (waveguide and multimode fiber) and amplitude (microscopic glass plates with stickers glued on it) microobjects using digital holography setup is presented. The measurement setup simulates the simplified arrangements for digital holographic tomography with two passes through the object. The experiment has proved the possibility of independent reconstruction of phase and amplitude for two different reconstruction distances for a certain class of objects. This allows to plan further activity aimed in development of digital holographic tomography system for 3D reconstruction of amplitude-phase objects.

Today's technological progress calls for metrologically accurate object measurement, positioning and scanning with nanometre precision and over large measuring ranges. In order to meet that requirement a nanopositioning and nanomeasuring machine (NPM machine) was developed at the Institute of Process Measurement and Sensor Technology of the Technische Universitaet Ilmenau. This device is capable of highly exact long-range positioning and measurement of objects with a resolution of less than 0.1 nm. Due to the structure of the machine many different probe systems can be installed, including scanning probe microscopes (SPMs). A few SPMs have outstanding metrological characteristics and many commercial microscopes only perform as image acquisition tools. Commercial SPMs use piezoelectric actuators in order to move either the sample or the probe. The position measurement sometimes results from the applied voltage to the piezoelectric actuators or from the strain gauge or capacitive displacement sensor data. This means that they suffer from hysteresis, creep, nonlinear characteristics and Abbe offsets. For an accurate measurement the position of the cantilever must be measured in addition to the torsion and bending. The best solution is a combined detection system with a single laser beam. This system has been realized with a special interferometer system, in which the measuring beam is focused on the cantilever backside using a lens. The reflected beam is split with a part being detected by a quadrant photo-diode and the other part being fed back into the interferometer for position measurement. The quadrant photo-diode is used to detect the cantilever torsion and bending.

We demonstrate a dual interferometric technique for simultaneous and independent measurements of the temperature dependence of the thermo-optic and thermal expansion coefficients in ferroelectric crystals. The crystal temperature can be changed from room temperature up to about 200°C by an actively stabilized heater (stability < 0.1°C). The thermal expansion coefficient is determined using a moire interferometer and monitoring the period of a grating written on the z-face of the crystal sample as a function of the temperature of the crystal. The thermo-optic coefficients of both ordinary and extraordinary axes are estimated by measuring the optical path variation measured by a Mach-Zehnder interferometer with one arm passing through the crystal perpendicularly to the crystal z-axis. This method can be applied to a wide variety of optical materials, when an accurate knowledge of the temperature dependence of the refractive index and thermal expansion is needed.

Research results obtained for local stress determination on micro and nanotechnology components are summarized. It meets the concern of controlling stresses introduced to sensors, MEMS and electronics devices during different micromachining processes. The method bases on deformation measurement options made available inside focused ion beam equipment. Removing locally material by ion beam milling existing stresses / residual stresses lead to deformation fields around the milled feature. Digital image correlation techniques are used to extract deformation values from micrographs captured before and after milling. In the paper, two main milling features have been analyzed - through hole and through slit milling. Analytical solutions for stress release fields of in-plane stresses have been derived and compared to respective experimental findings. Their good agreement allows to settle a method for determination of residual stress values, which is demonstrated for thin membranes manufactured by silicon micro technology. Some emphasis is made on the elimination of main error sources for stress determination, like rigid body object displacements and rotations due to drifts of experimental conditions under FIB imaging. In order to illustrate potential application areas of the method residual stress suppression by ion implantation is evaluated by the method and reported here.

MEMS as well as electronic components are used in the automotive, communication, aerospace and other industries. Miniaturization, higher package density and accelerated development processes have a great impact on the reliability of components. Rapid changes of ambient temperature or internal production of heat may occur during operation. This may create high thermal stresses due to the mismatch of the thermal expansion coefficients of the different materials in electronic components. On the other side simulations (FEA,...) are used in the electronic industry, but the material parameters (coefficient of thermal expansion, young's modulus,...) have to been known. A validation of results is necessary. In some cases simulations are not possible, than the measurement precise deformation is necessary. The 3D electronic speckle interferometry is a very powerful tool to investigate the thermal expansion of MEMS and electronic components. Due to the full field measuring technique combined with a high resolution the determination of critical areas and hot spots in electronic components is very easy. The capability of this measuring technique will be shown on examples like the NDT testing of flip chips, thermal deformation of BGA and a yaw sensor.

In this paper is reported a method for measuring the thickness of a silicone nitride layers employed for fabricating silicon MEMS bi-morph structures. The method allows the precise evaluation of layer thickness by adopting Digital Holographic Microscope. The measurement is based on the fact that the silicon nitride layer is transparent to the visible light. The optical phase difference (OPD) between the light beam traveling through the layer and portion of the beam in air is measured exploiting an interferometric technique. The approach is very simple and can be utilized even for inspection of non-planar or stressed structures. Experimental values have been compared with ellipsometric measurements.

The goal of this study was the investigation of reliability of AlN driven cantilevers, operating as MEMS actuators. Some of the fabrication steps being critical in regards to reliability issues, these steps have been firstly optimized. Then the monitoring of fatigue effects produced by thermal loading (130° C) of cantilevers, introducing the evolution of micromechanical parameters has been obtained by Twyman-Green interferometry. The measurements of evolution of resonance frequencies and displacement amplitudes permit the estimation of the long-term stability of such AlN based actuators.

We show the integration of a home-made interference optical microscope (IOM) with an Atomic force microscope, as well as the combination of IOM with a nanoindentor. Such combined instruments have many applications in the characterisation of MEMS/NEMS. As an illustrative example, we have used a MEMS accelerometer with capacitive read-out. Surface topography and defects have been measured with an IOM/AFM setup, as well as the bending and the torsion of the inertial mass while a calibrated force is applied with the nanoindentor probe on an off-axis location of the inertial mass.

Spatially Modulated Illumination (SMI) microscopy was applied to determine changes of the local refractive index at discrete fluorescently labeled sites within the cell nucleus. We present measurements on polymerase II complexes, where we found a variation of the local refractive index of 1.38 - 1.55 (standard deviation interval) throughout the nucleus. This variability is not correlated to the accumulations and the extensions of the polymerase II complexes, which have been determined in a previous experiment.¹ Local protein accumulations such as adherent transcriptionally active proteins could possibly contribute to such variations, as could also different compactions of the DNA fiber. Altogether, we present a method to precisely obtain a map of the local refractive index inside of cell nuclei, which provides another contrasting mechanism for visualizing sub cellular structures.

The present paper considers the use of X-Ray diffraction when applied for non destructive applications to surfaces with properties which are relevant for the qualification of the components of industrial plants or other related uses. The paper describes the most current worries related to calibration of diffractometers when they are used in laboratories; it introduces also a new approach to calculate the uncertainty of parameters related to the Bragg Equation. The approach implies to distinguish the Bragg angle from the effective angle occurring when settling a real experiment for x-ray diffraction measurements. Motivations are given for the introduction of such a new term. Moreover, based on recent networking experiences, a new conceptual approach to Round Robin test is given.

A flexible method of manufacturing polymer microlenses at the extremity of both single mode and multimode optical fibers has been previously developed. The procedure consists in depositing a drop of liquid photopolymerizable formulation on the cleaved fiber end and using the light emerging from the fiber to induce polymerization leading to the formation of a polymer tip. This process is highly interesting for applications in optical fiber connecting and SNOM imaging since it is fast, highly flexible (curvature radius can range from 0.2 to 100 μm) and does not require expensive equipment. Although the fabrication process leads to well-controlled geometrical structures, the mechanism of the polymer tip formation was not fully elucidated. In this work, we particularly focus on the photoinduced physico-chemical processes that occur during the lens formation. The effect of different parameters (irradiation time, light power, received energy, oxygen...) on the final properties of polymer tip (mechanical resistance, curvature diameter) was studied. The building up of the polymer tip was characterized by optical microscopy. This study allowed selecting the synthesis parameters leading to an improvement in the mechanical and optical properties of the polymer tip. From a fundamental point of view, this study appeared to be an interesting means to investigate the photostructuration of polymers at the micro- and nanoscales.

Micro injection moulding (micromoulding) technology has recently emerged as a viable manufacturing route for polymer, metal and ceramic components with micro-scale features and surface textures. With a cycle time for production of a single component of just a few seconds, the proces offers the capability for mass production of microscale devices at a low marginal cost. However, the extreme stresses, strain rates and temperature gradients characteristic of the process have the consequence that a slight fluctuation in material properties or moulding conditions can have a significant impact on the dimensional or structural properties of the resulting component and in-line process monitoring is highly desirable. This paper describes the development of an in-process, high speed 3-dimensional measurement system for evaluation of every component manufactured during the process. A high speed camera and microscope lens coupled with a linear stage are used to create a stack of images which are subsequently processed using extended depth of field techniques to form a virtual 3-dimensional contour of the component. This data can then be used to visually verify the quality of the moulding on-screen or standard machine vision algorithms can be employed to allow fully automated quality inspection and filtering of sub-standard products. Good results have been obtained for a range of materials and geometries and measurement accuracy has been verified through comparison with data obtained using a Wyko NT1100 white light interferometer.

In three-dimensional (3D) optical elements, light interacts with the element throughout its entire volume (as opposed to a discrete set of surfaces, which is done in traditional optics.) This allows for more degrees of freedom in shaping the optical response, in particular creating shift-variant responses. We have used this property in a number of ways to acquire 3D object information from both reflective and fluorescent objects under a variety of illumination conditions, including laser-line-scan, rainbow and uniform white light. The key benefits of using 3D optics are summarized as excellent resolution over long working distances, reduced or completely eliminated scanning, and simultaneous spectral imaging. Our research addresses the physics of 3D optical elements, their fabrication, and computational methods for maximal information extraction. In this paper, we first overview the properties of 3D optical elements and then we describe a fabrication and assembly method. Our approach, termed Nanostructured Origami, is appropriate for manufacturing micro-scale optical components which also include sub-wavelength optical elements and non-optical components, e.g. energy storage.

Optical profiling based on vertically scanning white-light interferometry is a well established 3D measuring technique for more than one decade now. In recent years the area of application of these instruments tends more and more from laboratory to industrial applications, where robustness, compactness, and cost efficiency is required. A new instrument developed on the basis of a Mirau interferometer with a microscopic field of view meets important requirements of industrial use. Surface heights can be obtained with subnanometer resolution and the measuring setup is less sensitive to vibrations, so that roughness measurements on optical surfaces are possible even in a harsh environment. However, principal limitations arise in certain applications, e.g. if optically smooth surfaces with either flanks, curvatures, edges, or grooves are to be measured. This contribution deals with phenomena, which become relevant in these cases. The occuring effects lead to differences in the results of coherence peak and phase analysis of the interference signals, and therefore may be the origin of ghost steps in the measuring results.

In this study we investigate the imaging mechanism of digital holography. The imaging process is separated into three steps: hologram recording, phase retrieval, and object field reconstruction. For hologram recording, the average effect due to the sensor pixel aperture and the role of the physical reference beam are addressed particularly. The average effect of pixel aperture is equivalent to a low pass filter, which acts on the interference term between the object field and the reference wavefront. An optimal physical reference beam is then to minimize the bandwidth of the interference term so that more object information can pass through the filter. For the reconstruction of object field, emphasis is paid on the correspondence between the underlying physical process and the discrete system represented by the reconstruction algorithms. The implication of sampling theory on each reconstruction algorithm is discussed in detail. The sampling requirement imposes a limitation only on the maximum extension of object field. Our analysis indicates that the achievable spatial resolution by digital holography is determined by the recording numerical aperture and wavelength of light, the same as the conventional microscopy. The independent analysis of each part illumines the way to optimize the system performance.

In digital holographic microscopy, a high numerical aperture object lens of good quality is required in order to achieve high lateral resolution. As well known, such lenses usually have large aberrations and are difficult to fabricate, especially in the ultra-violet and infrared spectral regions. In these circumstances, a system without objective lens is highly preferred. According to imaging theory, this means that the hologram should be recorded with a high numerical aperture (NA). For the reconstruction of high NA holograms, the Rayleigh-Sommerfeld diffraction integral without approximation must be evaluated. However the current mostly used three algorithms, namely, the Fresnel algorithm, the angular spectrum algorithm, and the convolution algorithm are not suitable. In this paper, the properties of these algorithms are presented. Then a modified convolution algorithm is proposed. In this method, a shift parameter is introduced in the discrete representation of diffraction kernel and then reconstructions with different shift values are combined. The modified convolution method is able to give samplings of diffraction-limited resolution for the full field of view. The simulation results of point field with different reconstruction algorithm are presented. Experimental results of a test dot array are also given.

The foundation pillars of successful technical products are performance, cost, and reliability. The development of reliable components and the operation of highly available systems is a comprehensive engineering task combining probability theory, materials science, and experience. Components have to be as reliable as necessary in order to build systems that are dependable and cost efficient during the whole life cycle. Reliability engineering is an ongoing process starting at the conceptual phase of a product design and continuing throughout all phases of a product life cycle. Theprimary objective is to identify and eliminate potential reliability problems as early as possible. While it may never be too late to improve the reliability of a product, corrections are orders of magnitude less expensive in the early design phase rather than once the product is manufactured and in service. This paper comprises an introduction to basic reliability engineering terms, reliability analysis methods such as reliability block diagrams, failure mode and effects analysis, Markov processes, the concept of redundancy, failure rate prediction models and the physics of failure approach, qualification and accelerated reliability testing. Examples of electronic and optical components, as well as complex opto-electronic systems and networks are given for illustration.

High numerical aperture cylindrical micro-lenses are needed in collimating the laser light from laser bars in the near infrared. Diffraction limited performance of such collimation lenses can only be obtained if the surface shape deviates strongly from circular symmetry. Therefore, null tests make the use of diffractive optical elements (DOE) necessary. For performance test at the design wavelength the reference DOE produces an ideal cylinder wave which enables the compensation of the wave front coming from the micro-lens to a plane wave. The use of a DOE-master enables beside the null test geometry also a removal of the anamorphic distortion due to the cylinder geometry. The DOEs having a numerical aperture of 0.8 are produced on an e-beam machine. The measurement of the wave aberrations is done with the help of the phase shifting technique. Alignment aberrations are eliminated by a least square fit of suitable misalignment functionals derived from an analytic approximation. The shape of the micro-lenses is tested in reflected light showing surface defects directly. The cylinder symmetry allows for a grazing incidence test using two DOE with nearly constant spatial frequency. There are no limitations concerning the test of high numerical aperture surfaces since the structure of the diffractive elements are parallel curves to the profile curve. The mean spatial frequency of the DOE defines the effective wavelength. Since we use a diffractive interferometer the effective wavelength is identical to the pitch of the DOE. Usually pitches between 4-10 μm are used resulting in a fringe sensitivity of 2-5 Μm. The test delivers the deviation of the surface from the ideal form. In the case of non-circular symmetry the DOE deviates from the axicon type DOE. In addition to the shape deviations also the radius of curvature at the vertex can be measured. The stage for the cylindrical micro-lens is equipped with a length measuring device using grating references from Renishaw providing a length increment of 0.1μm. With the axicon DOE there are two positions where nearly fluffed out fringes can be observed. Starting from the basic test position the lens can be moved until the vertex of the lens coincides with the focal line of the wave generated by the central part of the DOE. The distance between these two positions gives the radius of curvature for the vertex. Modern manufacturing of micro-lenses comprises also hot embossing in plastics or even into glass. Because of the small dimensions of the lenses and the required accuracy of the surface shape also tests of the impressing mould have to be carried out. The DOE approach enables also the test of the embossing form with the same sensitivity as the final test of the lens. Measuring results for the two test methods will be given.

Today there exist different commercial and proprietary 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 spherical 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 spherical microlenses.

In this paper we give an overview of the results obtained after benchmarking instrumentation tools for the characterization of micro-optics within the EC Network of Excellence on Micro-Optics NEMO. After a call within the NEMO network six different partners decided to organize a round robin. In this paper we will give an overview of all the experimental values obtained in the 6 different round robins, then we will comment on these results by explaining the measurement differences and the uncertainties for all measurands.

The paper presents a modular fiber optic sensing system to measure temperature, hydrostatic pressure and/or strain based on polarimetric highly birefringent fiber operating at infrared wavelengths. The main idea of such a system is a new replaceable fiber-optic head, which allows adjusting the measuring system both to the required range and type (strain, pressure or temperature) of the external measurand. The outputs of the modular sensing system characteristics have been optimized in view of enhancing their measurement capabilities and in order to minimize disturbing environmental effects.

A wireless displacement sensor is proposed which is composed of a fixed active head and a passive head which moves relatively to a grating scale. The passive head comprises a grating and two mirrors. It can be so small as to be inserted non-obtrusively where the displacement must be measured without spoiling the system optimum by undesirable size and structural compromises. It is insensitive to electromagnetic perturbations. The key characteristics of the sensor are high resolution and a very small size. The encoder uses a fixed grating scale as in standard designs, a passive-optical read head on the moving element and a stationary, opto-electronic source/detector module. Communication between the moving head and the detector module is done without cables using a free-space optical interconnection.

Micro-Electro-Mechanical Systems are nowadays frequently used in many fields of industry. The number of their applications increases and their functions become more responsible, therefore precise knowledge about their properties is necessary. Due to its fragility and small sizes non-contact and high sensitive measurement method is required. Two-beam laser interferometry is one of the most popular testing methods of microelements. Such method implemented in Twyman-Green interferometer allows for full-field shape determination and out-of-plane displacement measurement. However the elements under test may bring additional challenges: their surfaces may have complicated shape or large shape gradients which prohibit their testing by means of interferometer with a flat reference mirror. To overcome such problems we propose to use LCOS (Liquid Crystal On Silicon) - phase, reflective SLM as an active reference element. LCOS serves as an adaptive reference mirror and phase shifter. The use of such element allows increasing measurement range of the interferometer and simplifies out-of-plane displacement measurement through object wavefront compensation. The applicability of the modified Twyman-Green interferometer will be shown at the examples of active micromembranes testing.

Optimization of the optical quality of optical-grade germanium components requires an in-depth investigation of the different contributions to the optical loss in germanium. In this paper we therefore focus on this optical characterization. We give an overview of possible characterization techniques to determine surface roughness, surface/bulk absorption and refractive index inhomogeneities and we highlight the obtained optical characteristics. To conclude we select the most appropriate non-destructive characterization tool for each optical parameter.

In this work, the thermal characterization of a power MOSFET (Metal-Oxide-Silicon-Field-Effect-Transistor) using near infrared thermography method is presented. This characterization is based on the measurement of thermal radiation emitted by power transistor in the spectral domain ranging from 800 nm to 1000 nm. The thermal measurement is obtained in steady and dynamic mode and the absolute temperature distribution is measured at the micron scale. In dynamic mode, the transistor is heated (by Joule effect) at a frequency compatible with the camera acquisition speed. Results obtained in both modes highlight the excellent spatial resolution (optical resolution) of the experimental measurement apparatus and its great sensitivity for detection of weak thermal emission variations.

We present a laser interferometer where a narrow-line width tuneable VCSEL laser (Vertical-Cavity Surface-Emitting Laser) working at 760 nm is used. For the detection of an absolute distance, we have used a fast wavelength-scanning interferometry technique. In the first part of the work we introduce the absolute laser interferometer as a demonstrator for research of a digital detection of quadrature signals (X-cos and Y-sin). This interferometer uses polarized beams and magnitude division of interference fringes. The wavelength of VCSEL laser is swept with the mode-hop free tuning range more than 1.2 nm, by means of the amplitude modulation of the injection current. At the same time, the operating temperature of the VCSEL is stabilized with a fast digital temperature controller. We control the wavelength value and whole tuning process of the laser with the frequency lock to selected modes of an external Fabry-Perot etalon. Except the frequency lock, the Fabry-Perot mode spectrum identifies wavelength-tuning interval of VCSEL during each sweep. A digital signal processor (DSP) is heart of the control and detection system. It samples intensity signal from Fabry-Perot etalon and X-Y quadrature signals from the detection unit of the interferometer. After 1 nm sweep of the VCSEL wavelength, we obtain a number of passed interference fringes and the number of passed Fabry-Perot resonance modes, at the same time. On basis of these measured quantities we are able to calculate the instantaneous value of the optical path length difference between the measuring and reference arm of the demonstrational interferometer. The other part of the work is oriented to research and experimental testing of the digital detection of quadrature signals (X-cos and Y-sin) processed only on basis of one intensity signal (X-axis) that is produced by a simple photo-detector. On basis of traditional inversion function arctan(Y/X) we are able to determine instantaneous phase between interference beams in each part of recorded signals. In the work the first introduction of the method and measured records are presented.

Surface deformation inflicted on two different kinds of thin layered polymer films was investigated under static indentation and dynamic loading (plowing) at room temperature. Affecting the surface were polished spherical steel tips of 0.5-1.6 mm radii moving at 0.1-16.0 mm/s along the surface. A load of 2-5 N was applied on the tip normal to the surface. The surface response was measured with a scanning white light interferometer. The relation between groove parameters (width and depth) and the deformation tool velocity as well as the tip diameter and the applied load were obtained from white light interferometer scans. In order to cover a large groove area, a series of 3D groove profiles were stitched together with a piece of software. The profile of the entire groove was compared to friction data recorded by the scratching device. The dependence of groove parameters on the input parameters (tip radius, load force and velocity) indicates that white light interferometry can be used to determine mechanical properties such as 'scratchability' (abrasing resistance) of polymer surfaces without sample contact.

For high-tech industries, such as semiconductor or optical ones, controls must be done not only on airborne particle contaminants in cleanroom and associated controlled environments but also on surface particle contamination. Optical components are leading technologies for particle contamination control with atomic scale resolution over large areas. The aim is to enhance production reliability on miniaturized systems. Finding a correlation between such airborne and surface particle contaminations is the challenge we have to meet. This paper presents a methodology in order to answer this specific question. For, the latter depends on the cleanroom activity, operating personnel, cleanroom lay-out and equipment for example. Theoretically, we can calculate the surface particle contamination based on deposition velocities and deposition rates of airborne particle contamination defined in ISO 14644-1 for very simple cases. The reality is much more complex and the whole methodology presented here is based on experimental complementary measurements. The characterization of particle surface contamination is done mainly by light microscopy measurements and by optical particle counters...Complementary chemical data are obtained thanks to electronic microscopy with X-ray spectroscopy.

In this work we describe the design of a confocal microscope based optical system which can be used for two types of miniaturized fluid-chromatographic experiments: first of all for the study of shear-driven fluid separations in microchannels and secondly for the study of peak-broadening phenomena in pressure-driven fluids in the same type of microchannels. For the first type of measurements fluorescing dyes (coumarins) are used while for the latter type photo-active molecules (uncaged dyes) like for example fluorescein molecules are needed. We designed the detection system in such a way that by making some small changes to the system we can swap from one application to the other. After calculating the specifications of the optical components, we simulated the system with the sequential ray-tracing-software Solstis and built the system. Finally we did some preliminary experiments which demonstrated the working principle of our setup.

Array of fundamental Gaussian beams located on the surface of a hyperboloid of revolution forms a regular net of optical vortices whereas a resulting field represents a singular Bessel-Gaussian beam. A total topological charge of the beam is defined by a phase matching in the beam's array. Such simple key inferences were drawn from our theoretical analysis of light scattering with a stack of optical wedges. We experimentally found out that a Gaussian beam diffracted by a system of dielectrical wedges carried over central-positioned optical vortex, whose topological charge was equal to a number of wedges in the stack.

The round robin "measurement of subwavelength diffractive elements" tackles the metrology problems related to the measurement of diffraction gratings by AFM. It aims at quantifying the absolute precision and the uncertainty of the measurement considering some features of such structures like the depth, the period, the fill factor and the shape of the profile. This round robin involved four partners within NEMO. Each partner has measured three different samples: one 2D small depth grating, one 1D small depth grating and one 1D high aspect ratio grating. In order to get rid of the samples inhomogeneity, the measurements were performed exactly at the same location on each sample by all partners. This was achieved by using a multiscale resist pattern transferred on the gratings which precisely defined a 5×5 μm² area. The paper will sum up the experimental values obtained by all the partners, draw general conclusions and make suggestions to improve the accuracy of AFM measurements.

This contribution presents a new optical system, which allows real-time distortion measurement of weld-pieces on a laser welding machine. The system is based on simultaneous displacement measurement of several thousand points on a weld-piece surface employing rapid (non-scanning) laser profilometry. Weld-piece is illuminated by laser light, structured into multiple light planes and imaged by a digital camera. The position of the optical measuring system is fixed relative to the measured weld-piece. Acquired image is fed into a personal computer where it is processed to obtain the three-dimensional (3D) shape of imaged weld-piece surface. The maximum real-time measurement rate of the presented system is up to 20 surface measurements per second. We have applied the set-up to study the distortion of low-carbon thin steel sheet samples during Nd:YAG laser welding. In this paper we present characteristic evolution of surface distortion and distortion of the welding edges as a function of time. The produced weld-pieces exhibit characteristic V-shaped angular distortion mixed with longitudinal distortion, which bends down the welding edges at the end of weld. In welding edge distortion study we found out that the weld tends to annihilate vertical misalignment. The results show that the developed optical system allows fast and accurate temporally and spatially resolved evaluation of various types of weld-piece distortion. The presented system is scalable - the size of the measurement area can be adapted to the size of weld-piece.

A system for real-time surface deformations control during various types of laser processing is presented. It is based on a laser triangulation principle, where the laser projector generates multiple lines simultaneously. Three dimensional shape measurement of a surface is performed with a high sampling rate (80 Hz) and high accuracy (±7 μm). Results of steel-plate deformations are presented for laser bending, drilling and engraving. Laser based flattening process of previously deformed plate is demonstrated, where the measurement system is used as a feed-back control.