This PDF file contains the front matter associated with SPIE Proceedings Volume 7102, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Surface-enhanced Raman scattering (SERS) is a powerful spectroscopic tool for detecting low concentrations of many substances. The SERS effect occurs when a Raman active molecule is in contact with a metal surface having nanoscale features. While common SERS surfaces are formed on planar substrates, we present a technique whereby the surface is fabricated on the tips of custom designed optical fibres. The fibre presented is based on a modified imaging fibre which consists of a bundle of thousands of micron-sized individual optical fibres fused together in a coherent bundle. The fibre is then drawn such that each pixel is reduced to a nanoscale size. When chemically etched, the cores of the drawn pixels are eroded leaving an array of nanostructured wells. These are then coated with a thin layer of silver to enable SERS functionality. The design of the fibre, the manufacturing and etching processes and the characterisation of the SERS functionality will be presented.

Currently, the utilization of high power ultrafast lasers to induce optical changes in structures for the purpose of locally drawing patterns with dimensions inferior to the diffraction limit is well-established and controlled. Using this technique, we aim to modify the refractive index and/or the geometrical parameters of an optical interferential filter composed of successive thin layers. This local optimization will then allow the improvement or tuning of the performances of the optical filters. Thereafter, it is necessary to characterize these local modifications to achieve the final response of the expected filter. In our work, we developed a dedicated optical system, based on Fabry-Perot interferometry, to measure optical thickness, ranging from 10^-3 to 10^-4, with a high spatial resolution (in the order of 5×5μm). We present here our preliminary results carried out on calibrated test samples.

Sub-wavelength gratings allow to code complex transmittance functions that introduce both amplitude and phase variations in the propagation of a given wavefront. These micro-structures are a promising technique to miniaturize optical functions such as light polarizing, light confinement, spectral filtering... Realizations in the visible and the infrared domain have been fulfilled: for example micro-lenses, anti-reflection coatings or sinusoidal-transmittance can easily be coded. This technique is all the more advantageous in the mid-wavelength infrared (MWIR) or long-wavelength infrared (LWIR) spectral range since there are only a few materials available in this spectral range. However the characterization of these structures is problematical, since it involves phase and amplitude measurements. It is even more complicated in the far infrared domain (8 - 14 μm), as will be detailed. Besides, the finite size of the gratings introduces phase steps, which is well-known to be a problematic issue. We describe here a dedicated bench to characterize sub-wavelength gratings in the LWIR spectral range. The core of the bench is a quadri-wave lateral shearing interferometer based on a diffraction grating, which allows a complete two-dimensional characterization of both phase and amplitude in a single measurement. We present here theoretical and experimental results of a characterization of such a sub-wavelength grating.

Liquid lenses with adjustable focal length are of great interest in the field of microfluidic devices. They are, usually, realized by electrowetting effect after electrodes patterning on a hydrofobic substrate. Applications are possible in many fields ranging from commercial products such as digital cameras to biological cell sorting. We realized an open array of liquid lenses with adjustable focal length without electrode patterning. We used a z-cut Lithium Niobate crystal (LN) as substrate and few microliters of an oily substance to obtain the droplets array. The spontaneous polarization of LN crystals is reversed by the electric field poling process, thus enabling the realization of periodically poled LN (PPLN) crystals. The substrate consists of a two-dimensional square array of reversed domains with a period around 200 μm. Each domain presents an hexagonal geometry due to the crystal structure. PPLN is first covered by a thin and homogeneous layer of the above mentioned liquid and therefore its temperature is changed by means of a digitally controlled hot plate. During heating and cooling process there is a rearrangement of the liquid layer until it reaches the final topography. Lenses formation is due to the superficial tension changing at the liquid-solid interface by means of the pyroelectric effect. Such effect allows to create a two-dimensional lens pattern of tunable focal length without electrodes. The temporal evolution of both shape and focal length lenses are quantitatively measured by Digital Holographic Microscopy. Array imaging properties and quantitative analysis of the lenses features and aberrations are presented.

An overview of recent results in fabrication and application of new types of high precision CGHs for interferometric aspherical testing is presented.

The principle of a new scattering measurement system including a mobile lighting and a fixed CCD array is described. This new system allows a spatially resolved light scattering characterization. Moreover it is possible to separate localized defects contribution from the local roughness measurement. The comprehensive characterization of optical coatings can be performed with this set-up, and some examples will be given.

Application of dynamic X-ray lithography for originating of continuous-relief diffractive optical elements and microoptics has been investigated. The method is based on action of X-ray irradiation passed through fixed X-ray mask with triangle-like openings to periodically moved PMMA wafer. PMMA samples were exposed on synchrotron radiation facility VEPP-3 (BINP SB RAS, Novosibirsk) and then etched in liquid developer to form surface relief. Advances and limitations of the method have been discussed. Application of dynamic X-ray lithography with moving wafer to fabrication of gradient diffractive optical elements in PMMA wafer has been demonstrated.

Methodology of local characterization of continuous-relief diffractive optical elements has been discussed. The local profile depth can be evaluated using "approximated depth" defined without taking a profile near diffractive zone boundaries into account. Several methods to estimate the approximated depth have been offered.

The KBand Multi-Object Spectrograph (KMOS) is an astronomical spectrograph designed for integration with the VLT (Very Large Telescope) and capable of surveying 24 independent fields. The IFU (Integral Field Unit) subsystem is a complex instrument with no less than 1080 optical surfaces. We focus here on the design of the manufacturing and test process for this subsystem. Design of this system is based on experience gained on similar complex optical systems, such as the NIRSPEC (Near Infra Red Spectrometer) IFU that will be integrated into the James Webb Space Telescope. Surfaces are produced in aluminium using a freeform diamond machine. Many surfaces are multi-faceted and of complex form. The requirement for 15 nm RMS form accuracy poses a significant challenge for the machining process. In particular, the large number of highly complex surfaces represents the most serious design challenge. Design of the part fixturing is critical to the consistent achievement of the required surface accuracy. Furthermore, efficient test procedures must be developed to characterise all surfaces. In recognition of this, particular emphasis is placed on the metrology of these components. Moreover, the volume of complex metrology involved offers a unique opportunity to fully characterise and optimise the manufacturing process.

A new ultra precision large optics grinding machine, BoX ^(R) , has been developed at Cranfield University. This machine is located at the UK's Ultra Precision Surfaces laboratory at the OpTIC Technium, North Wales. This machine offers a rapid and economic solution for grinding large off-axis aspherical and free-form optical components. This paper presents an analysis of surface and subsurface damage assessments of Zerodur(R) ground using diamond resin bonded grinding wheels. Zerodur^(R) was tested as it is one of the materials currently under study for making extremely large telescope (ELT) segmented mirrors such as in the E-ELT project. The grinding experiments have been conducted on the BoX(R) grinding machine using wheels with grit sizes of 76 μm, 46 µm and 25 μm. The highest material removal rate (187.5 mm3/s) used ensures that a 1 metre diameter optic can be ground in less than 10 hours. The surface roughness and surface profile were measured using a Form Talysurf. The subsurface damage was revealed using a sub aperture polishing process in combination with an etching technique on small parts. These results are compared with the targeted form accuracy of 1 μm p-v over a 1 metre part, surface roughness of 50-150 nm RMS and subsurface damage in the range of 2-5 μm. This process stage was validated on a 1 metre hexagonal Zerodur^(R) part.

An outstanding technique in point of ultra-precision as well as economical production of mirrors is Single Point Diamond Turning (SPDT). The unique properties of the diamonds are used to get optical surfaces with roughness values down to 5 nm rms (root mean square) and very precise form accuracy down to 70 nm rms and 500 nm p.-v. (peak to valley) value over an area of 200 mm x 200 mm. This quality level is typical for applications in the Near Infrared (NIR) and Infrared (IR) range. For applications in the VIS and UV range the turning structures must be removed with a smoothing procedure in order to minimize the scatter losses. Favorable is an aluminium base body plated with a thick-film of Nickel-Phosphorus alloy (NiP). This alloy can be polished with computer assistance. Ion Beam Figuring (IBF) is the final manufacturing step. The properties after the finishing process are better than 1 nm rms for roughness and down to 15 nm rms respectively 100 nm p.-v. regarding the surface irregularity for complex optical shapes. The techniques SPDT, polishing and IBF ensures a high quality level for large mirrors with plan, spherical or aspherical surfaces. The manufacturing chain will be analyzed by surface characterisation based on 2D profilometry and white light interferometry to measure the roughness and 3D-profilometry and interferometry to monitor the shape irregularity. Scattering light analysis deepens these investigations. This paper summarizes technologies and measurement results for SPDT and surface finish of metal mirrors for novel optical applications.

Within the past ten years a variety of CNC manufacturers for aspherical surfaces have been established. The field of applications they are working for are very different. The way CNC manufacturers measure surfaces as well as the way they characterize the surface form deviation differs even more. Furthermore, there are a lot of customers being interested in using aspherical surfaces in their applications. In fact, aspherical lenses are not established as standard optical elements yet which is due to the fact that many users are not familiar with the implications of the use of aspherical surfaces with respect to the tolerancing of the optical system. Only few know how to specify an asphere, moreover, they differ about how to do that. The paper will give an insight in what is possible in aspherical manufacturing in terms of accuracy, efficiency, number of pieces per design and surface forms. An important issue is the development of deviation of form and slope in connection to prepolishing and correction polishing. Based on experiences of the manufacture of more than 500 different aspherical designs with diameters ranging from 3 - 200 mm, the paper is going to give an insight into production practices. Finally, there will be a general overview on what could be done and what needs to be done in order to unify the different ways of tolerancing of aspherical surfaces.

Spatially-engineered "top-hat" laser beams are used in solid-state high-energy lasers in order to increase the energy extraction efficiency in the amplifiers. To shape the laser beam, an efficient alternative to serrated apertures is to modify a laser cavity so that it naturally generates this "top-hat" beam, replacing a mirror of the laser cavity by a graded phase mirror. Its complex shape can be approached by microlithographic techniques based on an iterative mask and etch technique, but many steps are required to avoid large phase steps. The broad-beam ion-etching technique is well suited to manufacture such surfaces, with a good precision and a perfectly smooth surface. We shall present the technique we used for square top-hat beam generation. We shall detail the mask optimisation, combining simultaneous simulation of the ion etching and the beam build-up in the front-end laser. We shall present the results of the surface testing and the final test of the component in the laser.

The tremendous development of optical technologies and new manufacturing methods places challenging demands on metrology. Tools are required which allow for a rapid and sensitive inspection of the quality and homogeneity of surface finish even on large and curved surfaces. Light scattering measurements are best suited to meet these requirements. Recently developed instruments for scatter measurements at various wavelengths are presented in this paper. Examples of application are presented for diamond-turned and polished surfaces as well as for supersmooth EUV mirrors. In addition to laboratory-based instruments, compact and table-top tools currently being developed are briefly presented.

The design and manufacture of most optical systems revolves around the use of ideal optical surfaces. "Perfect" spheres or flats are optimally combined and toleranced during the design phase, and the manufacturers attempt to get as close as possible to these perfect optical surfaces during fabrication. One reason for this stems from the inherent capabilities of the industry's oldest and most pervasive polishing tool: the full-aperture lap. The shape and motion of these tools naturally produce spherical or flat geometries. More recently, a number of new manufacturing technologies based on sub-aperture polishing tools have become available. Sub-aperture tools enable local, preferential removal: a controlled way to polish more material at some locations and less at others. Magnetorheological Finishing (MRF^(R) ) is one such sup-aperture polishing technology, and when combined with an accurate measurement, can offer a precise method for converging to the perfect surface: local removal based directly on measured surface height. This capability, however, can also be leveraged in other, more creative, ways. For example, by replacing the typical surface-error measurement by a transmitted wavefront measurement of an entire low-field optical system, a hitmap can be created for one surface in the system that will perfectly compensate for errors of all the other surfaces. This paper will explore a number of examples where "perfectly bad" surfaces have been exploited in actual optical systems to improve performance, improve manufacturability, or reduce cost. In addition, we will ask the question: if making a "perfectly bad" surface was as easy as making a perfectly good one, would this capability be used more widely by the precision optics industry?

In the manufacturing process of aspheric glass lenses, the polishing step plays a key role with respect to the final quality of the lens as well as to the manufacturing costs. Due to the changing radius of curvature sub aperture tools are used for polishing aspherical lens elements. Even with small tools the changing radius has a significant influence to the wear function [1] [2]. This paper describes a method to calculate the removal based only on the surface shape and the material parameters of the tool. The described method can be used for any kind of surface, e.g. for freeform shapes.

For about 200 years surface shape specification for optical components always had one goal only, to make an individual optical component comparable with other pieces of the same type. If the specification is met, the component should fulfill the requested behavior in the related optical system. Nomenclature of specification did not differ in dependence on the components different position in the system or on different used beam diameters vs. components clear aperture. With increasing performance of designed optical systems, surface shape tolerances of components became tighter more and more. Such requirements either lead to inadequate expenses or to the absence of equipment to manufacture and test them in a controlled process. But in reality, only a small part of optical system components are used as they are measured - within full clear aperture. Moreover, the light beam has a significant smaller diameter than the clear aperture has. Typically, this kind of components we find in scanning systems and lenses with large Field of View (FOV). As far as designed surface shape tolerances are derived from maximal acceptable wave front deviation for individual light beams passing through the system, the related method for optical components acceptance test procedures is to analyze wave front deviation in sub apertures caused by surface shape deviation. In this case designed values and manufactured results are comparable to each other. To get the comparable values, surface shape analysis must be done in a gliding sub-aperture area instead of analysing full clear aperture. We show how sophisticated optical systems components may be specified, manufactured and tested in gliding subaperture areas for any term described in normative papers, such as ISO 10110-Part 5 "Surface Form Tolerances", to assure the final function in system. The chosen examples correspond with "classic specified" optical component surface shapes down to 3/ - (0.02)@546nm.

Laser beam homogenizing and beam shaping are key enabling technologies for many applications today. Periodic microlens arrays are widely used to transform Gaussian or non-uniform beam profile into a uniform "flat-top". Each microlens element samples the input beam and spreads it over a given angular distribution. Incoherent beams that are either temporally or spatially incoherent can produce very uniform intensity profiles. However, coherent beams will experience interference effects in the recombination of the beams generated by each individual microlens element. Rotating or moving elements, such as a rotating diffuser or a vibrating optical fiber, are used to average these interference patterns. An integration of several different patterns will smooth out the intensity profile. Unfortunately, this averaging is not always possible. Some applications require a single shot from a pulse laser or work at very high data rates that do not allow an averaging over 10 to 50 frames. We will discuss the concepts of Köhler illumination and Köhler integrators and its limitations and constrains for laser beam homogenizing. We will show how micro-optical elements comprised of a randomly varying component can be used to smooth out interference and speckle effects within the far-field intensity profile.

Conventional methods for objective measurement of the performance of image forming systems are reviewed. Due to the present widespread use of digital cameras, coupled with little data available on their actual performance, an alternative simpler approach for their comparative assessment has been studied. Camera performance, in this resolution-type test, requires measurement of a 'camera footprint' in relation to that of the 'visual footprint' of a standard eye. The metric,termed 'Optimum Print Width' (OPW) is defined as the width of print that can be made, when viewed at arm's length, where the effective size of the pixels in the camera are matched to the effective size of the cones in one's eye. The data are independent of magnification and take into account the number and size of spatially effective pixels, lens performance, image processing and, if needed, even the visual correction of the user. Performance data, collected from members of a camera-testing group, using several makes of camera are summarized.

Drawings of optical elements contain specification requirements on the properties of optical glass in most cases according to the standard ISO 10110 part 2 stress birefringence, part 3 bubbles and inclusions and part 4 inhomogeneity and striae. When ordering glass for the production of the elements sometimes uncertainties and misunderstandings occur, since the specification requirements on elements according to ISO 10110 cannot be transferred to the raw glass easily and clearly in any case. The reason is that raw glass may be delivered in very different shape: From close to net shape as pressings to far away from that as strip or block glass. Additionally in many cases an individual inspection by the glass supplier is not possible due to cost reasons or since it is not known at the time of delivery, which elements will be produced from the glass piece. Up to now an international standard was missing for optical raw glass. This standard ISO DIS 12123 is now close to final voting and release. This presentation provides the motivation for writing the standard, a comparison with ISO 10110 and information on the state and progress of standardization of optical glass.

The measurement of surface texture is one of the most common and important ways to judge the quality of a technical surface. In order to verify whether a metrology device is able to measure certain types of roughness accurately, various roughness standards with calibrated roughness values are available. While almost all roughness standards produced so far have been designed for tactile systems we demonstrate how the optical metrology device InfiniteFocus can be applied to special roughness standards that have been artificially roughened. Experiments are performed on standards with periodic structure and the results of the optical system are compared to the calibrated values obtained by tactile systems with different tip radius. Additionally the profile-based measurements are compared to area-based measurements conform to a recently developed ISO standard draft. Finally roughness measurements on real surfaces are presented.

Multi-component fringe projection sensors allow the fast, holistic, exact, robust, contact free sampling of a workpiece surface. The success of an inspection relies on the skills, diligence and experience of the inspection planner. For setting up an inspection, there is no standardized method established yet. Therefore there is a need for assistance systems to support the operator. A prototype of an such assistance system for multi-component fringe projection sensors is introduced. The assistance system supports the inspection planner in determining the ideal sighting- and positioningstrategy. As key element, the result of a planned inspection is simulated. First, the optical performance of the designated fringe projection sensor is calculated by use of raytracing software. Then the measurement result and the measurement uncertainty for specific measurement tasks and a chosen measuring pose, is simulated. Fundament for this simulation is a complete mathematical-physical model of the measurement. Building on this and on the knowledge of influences, which were previously inscribed in entry masks, the measurement uncertainty can be estimated and displayed individually for each point of a workpiece surface. Thus the inspection planner can easily evaluate the quality of the planned inspection setup. Additional optimizing algorithms were implemented. The aim of the multi-criteria optimization is to determine the best configuration for the measurement device and the ideal sighting- and positioning-strategy. As measure of quality serves hereby the reduction of the measurement uncertainty.

To ensure the performance of optical systems for space applications, the design of the mounts for the optical elements and the choice of materials are crucial. Beside this also the applied bonding techniques are playing a major role. The alignment of the optical elements must remain after the loads of the launch phase and in the thermal environment of the satellite. We present our achievements in alignment accuracy and stability during assembly and integration of optical systems for space applications in the case of two very different examples: In the first example we bonded prisms to a baseplate using a radiation activated optical adhesive. The achieved alignment accuracy was better than 3". In the second example we bonded Zerodur mirrors with diameters up to 150 mm and mass of 1 kg to Invar mounting frames using a slow curing two-component adhesive. Here the achieved alignment accuracy was in the order of 10". Thanks to our sophisticated bonding techniques and specially designed mounts and bonding jigs, these alignments were preserved during environmental tests like thermal cycling and vibration tests.

Shack-Hartmann wave front sensors (SHS) are an accurate and highly versatile tool for characterizing and adjusting high performance optical systems, especially in the DUV wavelength range. The conventional set-up uses a single path approach. An illuminated pinhole is placed in the object plane and the sensor in the exit pupil of the system under test. This approach is applicable up to a NA of about 0.9 because of the limited ability of a pinhole to illuminate high numerical apertures. Beyond the limit a double pass set-up is necessary. The double pass approach also allows a higher precision and the application of multi-position tests well-known from interferometry. A set-up will be shown which can be easily integrated into existing Shack-Hartmann test benches. Some exemplary data will be given comparing results from single pass and double pass measurements.

We present the application of Quadri-Wave Lateral Shearing Interferometry (QWLSI), a wave front sensing technique, to characterize synthetic intraocular lens (IOL). Wave front sensing is not only a tool to quantify optical quality, but also to map the local (dust, scratches) or global possible defects. This method offers the crucial advantage that it yields an analyzed wave front without the use of a reference arm and consequent time consuming alignment. Moreover thanks to the acceptance of QWLSI to high numerical aperture beams, no additional optics is required. This makes lens characterization convenient and very fast. We will first explain the QWLSI design and metrological properties (high resolution and dynamic) and its analysis features (aberration measurement, MTF evaluation). We will present our device KALEO for characterization of IOLs. We will particularly show aberrations and MTF measurements of monofocal spherical IOLs. We will present how the QWLSI can answer to the specific analysis of aspherical IOLs. We will finally show a complete characterization of multifocal IOLs in one measurement helping the propagation theory.

The radial and axial point spread function (PSF) and the 3D modulation transfer function (MTF) were calculated to demonstrate the influence of phase only filters in classical optical imaging systems. The 3D line spread function (LSF) makes it possible to discuss the influence of the degree of coherence in the optical imaging system with the phase only filter as well. First, the phase only filter under discussion was divided in five equally area annuli. The phase variations are either linearly increasing or decreasing with the annulus number or alternating between 0 and π. Second we have used a filter that consists on one phase annulus with a phase shift of π in different positions over the pupil. Numerical and experimental results are shown in this paper. A spatial light modulator (SLM) was used to obtain experimentally the influence of the different phase only filters on the image of a sector star. The merit functions for filters with a phase shift of π in one annulus are also studied. These filters produce a wide variety of responses in dependence of the position of the phase shifting annulus. By studying the merit functions, a clear prediction of the imaging behaviour of an optical system is possible as well. The conclusion of our work has been that it is necessary to study the influence of the filter on the different merit functions in order to design an optimum filter for a given application.

This paper discusses the architecture of software utilized in spectroscopic measurements. As optical coatings become more sophisticated, there is mounting need to automate data acquisition (DAQ) from spectrophotometers. Such need is exacerbated when 100% inspection is required, ancillary devices are utilized, cost reduction is crucial, or security is vital. While instrument manufacturers normally provide point-and-click DAQ software, an application programming interface (API) may be missing. In such cases automation is impossible or expensive. An API is typically provided in libraries (*.dll, *.ocx) which may be embedded in user-developed applications. Users can thereby implement DAQ automation in several Windows languages. Another possibility, developed by FTG as an alternative to instrument manufacturers' software, is the ActiveX application (*.exe). ActiveX, a component of many Windows applications, provides means for programming and interoperability. This architecture permits a point-and-click program to act as automation client and server. Excel, for example, can control and be controlled by DAQ applications. Most importantly, ActiveX permits ancillary devices such as barcode readers and XY-stages to be easily and economically integrated into scanning procedures. Since an ActiveX application has its own user-interface, it can be independently tested. The ActiveX application then runs (visibly or invisibly) under DAQ software control. Automation capabilities are accessed via a built-in spectro-BASIC language with industry-standard (VBA-compatible) syntax. Supplementing ActiveX, spectro-BASIC also includes auxiliary serial port commands for interfacing programmable logic controllers (PLC). A typical application is automatic filter handling.

At 193nm and 527 nm, the laser induced deflection (LID) technique is applied to measure directly and quantitatively residual absorptions in high reflecting optical coatings. In addition, combined measurements of absorption, transmission, reflectivity and scattering for HR mirrors at 193 nm reveal very good results for the energy balance. Cavity ring down (CRD) spectroscopy is a sensitive technique to characterize highest mirror reflectivities by determine the photon lifetime within a resonator. A CRD setup, designed for both, cw and pulsed lasers, serves for measurements. First measurements at λ = 532 nm reveal ultra high reflectivities of r ≥ 99.99 %. Accompanying, residual absorption of HR coatings (ppm range) is measured directly by LID technique to quantify the different loss mechanisms contributing to the CRD result. Additionally, the CRD setup is applied to determine the total bulk loss of (58 ± 25) ppm/cm in fused silica at λ = 675 nm by measuring a thickness series.

Significant improvement in polishing processes of fused silica optical components, has increased optics lifetime at the wavelength of 351 nm. Nonetheless, for large laser operation facilities like the Laser MegaJoule (LMJ), zero defect optics are not yet available. Therefore a damage mitigation technique has been developed to prevent the growth of initiated damage sites: this technique consists in a local melting and evaporation of silica by CO2 laser irradiation on the damage site. Because of the difficulty to produce efficient mitigated sites with large depth, the initial depth of damage to mitigate is a critical issue. An aim of our work was to determine the real extension of the damage site (including fractures) for different laser pulse durations between 3 ns and 16 ns and at different laser fluences. The fractures are nondetectable in conventional microscopy. The depth of the damage can thus be underestimated. Hence confocal microscopy, was used to observe these sub-surface fractures and to measure precisely the depth of damage. Results show that the damage is 2 to 4 times wider than deeper and this ratio is independent of the pulse duration and of the fluence. With this new information, the mitigation process can now be optimized.

Research experiments and advanced applications often require the knowledge of the refractive index of vitreous materials under specific environmental conditions. Measurements are carried out by placing the glass sample in a cell where the required conditions are established; the probe beam enters and exits the cell through a pair of windows. A typical case is the measurement in vacuum, as it occurs when thermal cycles down to cryogenic temperatures have to be performed. In such a case, data processing has to take into account the specific geometry of the cell and the windows. Here we present closed formulas for a symmetrical configuration, and a ray tracing approach for general cases where symmetry is not guaranteed. In particular, the experimental configuration is conveniently modeled, and ray tracing is used to find out the conditions of minimum deviation, starting from a tentative value of the refractive index. The latter is successively modified until the data actually obtained from experiments are matched. Specific software is developed, accomplishing the computation task automatically by recursive iterations. The ray-tracing model is also used to numerically estimate the sensitivity of the results to the influence variables, and to work out the uncertainty balance.

The temperature-dependent dispersion of the refractive index of optical materials is analyzed by introducing an appropriate formulation of what we call their "normalized thermo-optic coefficients" (NTOC). These parameters are obtained experimentally by performing accurate interferometric measurements of both thermal expansion and changes in optical thickness of parallelepipedic shaped samples of millimetric size which are submitted to a linear ramp of temperature. Changes in optical thickness are recorded as function of temperature at a few discrete laser wavelengths; they are expressed as power series of temperature and the use of a simple vectorial formalism allows then to determine the thermal behavior of the dispersion law over the whole transparency range of the material. The validity and reliability of the proposed method has been confirmed by modeling the temperature dependence of the type II second harmonic generation 1.064 μm - 0.532 μm in a KTiOPO₄ single crystal, recorded up to 120°C.

Parabolic mirrors can be tested by means of diffraction-generated test beam technique. The parabolic mirror under test focuses the collimated laser beam from Fizeau digital interferometer. When a very small diffraction element is placed at the focal point, it diffracts the focused light and generates a spherical wave in the test arm. This spherical wave from the focus is reflected back to the interferometer by the parabolic mirror under test and services as a test beam. The optical path difference (OPD) between the test wavefront and a plane reference wavefront indicates the surface irregularity of the parabolic mirror in terms of interference fringes. There is no central hole in on-axis parabolic mirror testing. Experiments have been carried out to test high-precision parabolic mirror.

The wavelengths associated to the transmission peaks of a Fabry-Perot etalon are directly connected with its optical thickness. As a consequence, any change in the physical thickness or the refractive index of the cavity has a direct influence on the value of these specific wavelengths. This property can be used to determine the thermal characteristics, like the coefficient of thermal expansion or the thermo-optic coefficient, of some materials. However, to be efficient, this method needs a very high accuracy in the determination of these resonant wavelengths. We developed a dedicated measurement set-up, combining a tunable laser source around 850 nm and a high precision wavelength meter to determine with accuracy better than 0.2 pm the resonant wavelengths of a Fabry-Perot etalon. We use a temperature stabilized chamber to avoid temperature fluctuations or, on the contrary, to apply a deterministic temperature change at the cavity level. We describe the structure of our bench and present the results obtained on BK7 windows as well as on an optically contacted ULE Fabry-Perot with silver coatings.

While scatterometry of macroscopically plane rough surfaces by using quasi-parallel illumination is widely investigated, measuring light scatter from rough surfaces with a certain macroscopical curvature leads to the problem of separating the effects of micro-roughness from those of curvature in the scatter distribution. This is especially true for micro-roughness far beyond the smooth surface criterion. So for example, the scatter distribution of a cylinder with heavy traces of machining along a plane through the axis of rotation will be wide-spread perpendicularly to that plane for both reasons, the scatter pattern of the machining marks and the curvature of the surface. The curvature can be compensated by means of additional aspherical optical systems. In principal, this can be achieved by adaption of the illumination system or the receiver optics. Also both ways can be applied. The current paper deals with various design approaches theoretically and practically and gives some comparative measurement examples from actual applications for compensated and uncompensated systems.

We report the results of utilization of wide-gap photorefractive sillenite crystals as adaptive photodetectors (AP) for optical inspection of micro-electromechanical systems. The operation principle of AP is based on two-wave mixing and non-steady-state photoelectromotive force effects in photorefractive crystals. The results of measurements of small vibration amplitudes and resonant frequencies of the diffusely scattering objects and micro-electromechanical systems are given. The presented adaptive interferometric systems are suitable for industrial applications.

A new system for characterizing the flow delivered by a Laval nozzle in different stream configurations has been designed, developed, settled and tested. An optical module (Mach-Zehnder interferometer), an acquisition module (CMOS camera) and a processing module (Fourier Transform Phase Difference Method) have been integrated and assembled in order to obtain the instantaneous optical phase distribution along the gas flow. An additional postprocessing numerical stage provides gradient and Laplacian information of the optical phase distribution and allows a complete modeling of the fluid flow. In this work the main results, advantages and limitations of the metrological protocol related with a detailed measurement campaign are presented. Also the analysis of the obtained optical phase difference distribution is compared with results given by a tailored processing numerical stage.

Optical vortices have been applied for the purpose of polarimetry measurement. Vortex polarimetry combines the features of null polarimetry and imaging Fourier polarimetry providing one shot measurement. Different polarimeter systems and limiting accuracy factors are discussed.

The French Commission for Atomic Energy is currently involved in a project which consists in the construction of a 2MJ/500TW (351nm) laser, so called LMJ (Megajoule-class laser) devoted to Inertial Confinement Fusion (ICF) research in France^[1]. For this high power lasers, the sol-gel process^[2] has been selected for 95% of laser optical coated area because of room temperature and atmospheric pressure conditions with guarantee for high optical and laser induced damage threshold (LIDT) performances at a low cost compared to conventional vacuum deposition processes. The production rate of sol-gel coatings for the LMJ optical components will require an automated cleaning surface step during sol-gel process. We are investigating a spraying system and wash cycles compatible with the two sol-gel deposition methods: dip and laminar-flow coating. The challenge is to achieve the same cleaned optical surfaces as manual process without using organic solvents. Therefore the main specifications of the cleaning quality are the following ones: a high surface energy over all optical sides (up to 400×400 mm² area) and no degradation of polished sides (surface defects and LIDT). We present the metrologies carried out and the first results obtained from different wash cycles. These one mainly consist in measurement of contact angles, defects inspections under specific lighting conditions and LIDT tests. Several parameters of wash cycles have been investigated such as washing and rinsing temperatures, water quality, type and concentration of detergents, wettability effects...

Herschel space observatory of ESA has a parabolic M1mirror of silicon carbide (SiC) with large diameter of 3.5 m, fast focal ratio of f/0.5 and extreme light-weighting to 25 kg/m², which make the polishing of the mirror a very challenging task. Use of very high surface pressure is necessary to polish efficiently this hard material, which increases the risk of quilting effects to the shape of the only 2.5 mm thick front face of the mirror. In this paper we present descriptions of the testing and polishing methods used during Herschel M1 lapping and polishing to the specified surface shape accuracy < 1.5 μm rms and micro roughness <30 nm rms.

The Aladin instrument on the ADM-Aeolus satellite of ESA has a parabolic M1 mirror of silicon carbide (SiC) with diameter of 1.5 m, fast focal ratio of f/0.9 and light-weighting to 25 kg/m². The lidar instrument is operated at the near ultraviolet wavelength of 355 nm, which requires high optical quality and good smoothness of the polishing finish. In this paper we present descriptions of the testing and polishing methods used during ALADIN M1 lapping and polishing to the specified wave front shape accuracy <150 nm rms and surface micro roughness < 5 nm rms.

Differential Phase-Shifting Algorithms (DPSAs) recover directly the phase difference encoded in two patterns being unnecessary the previous calculation and subtraction of each individual optical phase by means of well-known highly efficient and accurate Phase-Shifting Algorithms (PSAs). In spite of their interesting metrological applications, there are almost no published studies about the possible error-compensating methods in DPSAs, so it is necessary to investigate the tools to eliminate or minimize the inevitable effect of the principal errors on the measurement process. In previous works we have linearized and numerically simulated phase shifting errors and the presence of harmonics on the signal of several families of DPSAs obtaining analytical phase error expressions. In this paper we present an analysis of propagation errors for several DPSAs families considering, in a similar way than in PSAs, the frequency shifting property of the employed arctan function. A Fizeau phase-shifting interferometer is employed to verify the main characteristics of the analysed DPSAs families.

The controls by optical mean of coatings deposited on optical components are generally made with flat witnesses. When the components are spherical or aspherical, like lenses or mirrors, the spectral response may vary because of the nonuniformity of thickness that is really linked to the deposition process. For large radius of curvature, control can be achieved even with classical spectrophotometers. However, control becomes more and more difficult when the radius of curvature decreases or when the optical device has a complex shape. Thus special devices are needed to perform this kind of measurement. ZEISS and CEA Le Ripault use spectral reflection as a mean of measurement, which enables to investigate optical coatings on curved parts. Two different devices have been implemented and used to measure the same antireflective coating deposited on an aspheric lens. In this work, we show the obtained results and we compare these results to theoretical simulation.