This PDF file contains the front matter associated with SPIE Proceedings Volume 8169, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Deterministic final polishing of high precision optics using sub-aperture processing with magnetorheological finishing (MRF) is an accepted practice throughout the world. A wide variety of materials can be successfully worked with aqueous (pH 10), magnetorheological (MR) fluids, using magnetic carbonyl iron (CI) and either ceria or nanodiamond nonmagnetic abrasives. Polycrystalline materials like zinc sulfide (ZnS) and zinc selenide (ZnSe) are difficult to polish at pH 10 with MRF, due to their grain size and the relatively low stiffness of the MR fluid lap. If microns of material are removed, the grain structure of the material begins to appear. In 2005, Kozhinova et al. (Appl. Opt. 44 4671-4677) demonstrated that lowering pH could improve MRF of ZnS. However, magnetic CI particle corrosion rendered their low pH approach unstable and unsuitable for commercial implementation. In 2009, Shafrir et al. described a sol-gel coating process for manufacturing a zirconia-coated CI particle that protects the magnetic core from aqueous corrosion (Appl. Opt .48 6797-6810). The coating process produces free nanozirconia polishing abrasives during the coating procedure, thereby creating an MR polishing powder that is "self-charged" with the polishing abrasive. By simply adding water, it was possible to polish optical glasses and ceramics with good stability at pH 8 for three weeks. The development of a corrosion resistant, MR polishing powder, opens up the possibility for polishing additional materials, wherein the pH may be adjusted to optimize effectiveness. In this paper we describe the CI coating process, the characterization of the coated powder, and procedures for making stable MR fluids with adjustable pH, giving polishing results for a variety of optical glasses and crystalline ceramics.

The Laboratoire d'Astrophysique de Marseille (LAM) is involved in the prototyping of a full scale demonstrator for stress polishing of segments for the European Extremely Large Telescope (E-ELT). Stress polishing method is developed at LAM since more than 40 years, and this mature technology has recently been used with success for VLT instruments. Stress polishing is now considered as a promising manufacturing method for mass production of large off axis mirrors, specifically for ELT segments. This powerful method, based on elasticity theory, allows the generation of super-smooth off-axis aspherics with a minimal amount of high spatial frequency ripples by spherically polishing a warped blank with a full-sized tool. Thanks to the simple spherical polishing, the operation time can be strongly reduced compared to the time-consuming sub-aperture tool methods of grinding and polishing. The goal is to rapidly converge to less than 1 micron RMS of optical quality on a circular blank which will be finally cut hexagonally and finished using Ion Beam Finishing. In this paper we will present the status of the demonstrator and the design of the warping harness prototype that must be able to precisely warp the circular blank.

After a brief introduction of what is the Dark Energy Survey (DES) project and which optical instrumentation will be used, the presentation will be mainly focused onto the optical production of the large lenses (up to 1m diameter) constituting the DES Camera (DECAM) located at the focal plane of the main observing telescope. Special emphasis will be made onto the optical manufacturing issues and interferometric testing solutions, including compensation of index inhomogeneities, which have been carried out by SESO especially for the biggest entrance lens (very challenging CV/CX meniscus named C1). Through several examples of typical past realizations or future possible ones for different astronomical projects requiring 1m-class optics, the presentation will conclude by a brief over review of the corresponding existing "state of the art" at SESO for these technologies.

Sagem is presently working on a new project for the Japanese HISUI instrument made from a Hyper Spectral Sensor and a Multi Spectral Sensor, both including a Three Mirror Anastigmat (TMA) main optics. Mirrors are made from Zerodur from Schott but also from NTSIC, the New Technology Silicon Carbide developed in Japan. This report is also the opportunity to show to the community Sagem recent progress in precision TMA optics polishing and alignment.

The time stability of fused silica is investigated, reporting new data on two flats that were purchased in 1981. It is found that their present shape is no more plane, exhibiting instead a concavity that is compatible with a very slow laminar flow under the action of gravity. The data are examined altogether with those of prior observations, confirming the occurrence of a relaxation process whose time constant is estimated in the order of 10 years; during such a time period, viscosity approximately increases by a factor of three. Starting from the experimental data so far collected, the computations accounting for the estimates above are given in detail.

Imaging Fourier Transform Spectrometer working in the far UV (IFTSUV) may be the technical solution to answer many unsolved problems concerning the physics of the solar outer atmosphere. The VUV domain highly constrains the instruments design and performances as it demands a high optics surface quality and an accurate metrology to preserve IFTSUV spectral precision and Signal to Noise Ratio (SNR). We present the advancements on the specification of a metrology system, meeting the predicted performance requirements of an IFTSUV.

In this paper, we propose a method named as AMAI-PCA to extract aberration levels using aerial image measurements and present its experimental results on lithographic tools. Based on physical simulation and statistical analysis, a linear regression matrix is obtained establishing a connection between principal component coefficients of specific aerial images and Zernike coefficients. In the application phase, the aberrations of the projection lens are solved via the use of this regression matrix. An engineering model is established based on an extension of theoretical model that incorporates all the significant systematic errors. The performance of the engineering model applied on a 0.75 NA ArF scanner is reported. In the experiment, measurement marks oriented in orthogonal directions are used and aerial images on 9 field points are measured. To verify the repeatability of this technique, every point is measured 20 times. By inputting the aerial images into the engineering model, Zernike coefficients are solved and the results are analyzed. The wafer exposures were performed to evaluate the results of aberration correction.

Ronchi test represents an economical alternative, with ease implementation and uncertainties in the order of wavelength, to measure the piston between the elements of a segmented mirror. The current trend of using non monolithic surfaces as imaging systems in telescopes or adaptive optical systems in medical devices, open the field for the development of new wavefront sensors that would retrieve information allowing an optimal disposition of the segments to form an image with minimum of optical aberration. This paper uses the Ronchi test to reconstruct the wavefront, and measure the piston between two adjacent mirrors. Based on a geometrical relation, we have developed a computer software that determine the distance between the mirrors and the light source using a nonlinear optimization algorithm. In order to achieve this goal, it is necessary to perform a several stages processing to the input images. Finally, the wavefront reconstruction is carried out using a combined nonlinear optimization and least square algorithm.

Micro-optics is an indispensable key enabling technology (KET) for many applications today. The important role of micro-optical components is based on three different motivations: miniaturization, high functionality and packaging aspects. It is obvious that miniaturized systems require micro-optics for light focusing, light shaping and imaging. More important for industrial applications is the high functionality of micro-optics that allows combining these different functions in one element. In DUV Lithography Steppers and Scanners an extremely precise beam shaping of the Excimer laser profile is required. High-precision diffractive optical elements are well suited for this task. For Wafer-Level Cameras (WLC) and fiber optical systems the packaging aspects are more important. Wafer-Level Micro-Optics technology allows manufacturing and packaging some thousands of sub-components in parallel. We report on the state of the art in wafer-based manufacturing, testing and packaging.

Structuring of optical surfaces with surface-relief diffractive optical elements is an enabling technology for achieving considerable spatially varying changes in light propagation direction and wavefront curvature. This way, Bragg effects, angular and spectral selectivity and nearly 100% diffraction efficiency usually attributed to volume optical holograms can be achieved by surface relief computer generated holograms and diffractive optical elements. Several methods for fabricating deep "resonance domain" diffraction structures with periods, exceeding the subwavelength limit but near to the wavelength, were compared and optimized. Results of direct e-beam writing RIE etching, SEM and AFM measurements for fused silica gratings with period of 520 nm and groove depth of 1000 nm, designed for nearly 100% diffraction efficiency in the green 532 nm laser light, are presented.

Fresnel lenses and other faceted or micro-optic devices are increasingly used in multiple applications like solar light concentrators and illumination devices, just to name some representative. However, it seems to be a certain lack of adequate techniques for the assessment of the performance of final fabricated devices. As applications are more exigent this characterization is a must. We provide a technique to characterize the performance of Fresnel lenses, as light collection devices. The basis for the method is a configuration where a camera images the Fresnel lens aperture. The entrance pupil of the camera is situated at the focal spot or the conjugate of a simulated solar source. In this manner, detailed maps of the performance of different Fresnel lenses are obtained for different acceptance angles.

Stellar coronagraphs using circular phase masks are promising concepts dedicated to the image suppression of an observed bright star in order to enhance the substellar mass companions present in its vicinity, typically 2 λ/D angular separation. These concepts include a focal plane phase mask which introduces a phase delay on a part of the stellar image. With an adequate choice of the mask parameters (thickness, diameter), the light going through the mask and the light going outside the mask will interfere destructively inside the geometric pupil in the following pupil plane. The light rejected outside this re-imaged pupil will be blocked by a Lyot stop. Typically, the mask physical size is about λF, where F denotes the f-number of the optical system, and the mask thickness depends on the required phase shifting. The contrast provided by these concepts is highly related to the quality of thickness profile of the phase mask and therefore, severe manufacturing tolerances are necessary to reach the theoretical performance of the corresponding coronagraphic system. In 2007, we designed a Roddier & Roddier phase mask with a 65 μm diameter and ordered it to GEPI of Paris Observatory which manufactured it using ion etching process. A roughness of 0.8 nm rms and a transition width of 1% of the mask diameter were measured with a profilometer for this mask showing the good quality of the mask (N'Diaye et al. 2010). We pursue our efforts to design and manufacture high quality masks in collaboration with the firm SILIOS. Several tests of manufacturing procedures are currently realized to reach the best trade-off between mask roughness and mask transition width. These values, measured in our laboratory with a profilometer, allow us to determine the best configuration for fabrication. In addition, by knowing the mask profile, we can estimate theoretically the performance that can be reached.

A bilayer wire grid polarizer composed of UV-replicated nanograting and deposited aluminum layer was designed, fabricated and evaluated for a simpler and less costly reflective polarizer. An electroformed nickel stamp was fabricated using a lithographed photo resist master pattern having a nanograting with a pitch of 80 nm, a line width of 50 nm, and a height of grating of 100 nm. A polymer grating was fabricated by the UV replication process and an aluminum layer with a thickness of 50 nm was deposited by electron-beam evaporation. To examine the performance of the fabricated bilayer wire-grid polarizer, the transmission spectra of TM- and TE-polarized light, and the extinction ratio spectra were measured and compared with the simulated values obtained from the rigorous coupled wave analysis. The measured TMtransmittance and extinction ratio of the fabricated bilayer wire grid polarizer were ~ 40 % and ~ 103 in whole visible ranges, respectively.

Losses due to the scattered light are known to be a key limitation of optical components performances. Hence a challenge consists in identifying and quantifying the scattering sources with high accuracy. In this context, dedicated techniques and facilities were developed at Institut Fresnel. Numerical and metrological platforms dedicated to light scattering characterization and modelization were created and are be presented in this paper.

Characterization of the spectral transmission of micro-patterned optical coatings requires accurate and highly localized measurement means. However, the capabilities of commercial equipments are generally limited, and either they do not provide sufficient spatial and spectral resolution, or they modify the spectral transmittance properties of the sample by using a large half angle illuminating light cone. In this work, we propose a new approach based on the recording, using a high performance photodiode array camera, of monochromatic magnified images of the sample illuminated by a filtered and fiber-coupled super-continuum laser source. In such case, the spatial resolution is directly given by the size of the individual CCD pixels and by the magnification of the imaging objective, while the spectral resolution is defined by the slit width of the filtering monochromator. This paper will give a detailed description of the main features of this spectrophotometric bench, and will demonstrate its ability to record the spectral transmittance of patterned samples with micrometer spatial resolution and sub-nanometer spectral resolution in the visible and near infrared ranges.

For high speed quality control in production we had developed a novel approach for fast ellipsometric measurements. Instead of a conventional setup that uses a standard photo-elastic modulator, we use a Single Crystal Photo-Elastic Modulator (SCPEM), for which in this case a LiTaO₃-crystal is used. Instead of an analog Lock-In Amplifier, an automated digital processing based on a fast analog to digital converter is used. This small, simple, and cost-effective solution with its extremely compact and efficient polarization modulation allows fast ellipsometric testing where the upper limit of measurement rates is only limited by the desired accuracy and repeatability of the measurements. Now we present an extension of this measurement from 635nm in the VIS to 1064nm in the NIR and discuss the related problems with signal measurement and retardation control. Further the system speed was enhanced by onboard processing, such that now a sampling rate of 46 kHz is possible.

Optical components for extreme ultraviolet (EUV) lithography at a wavelength of 13.5 nm face tremendous requirements on the surface finish, because large amounts of the EUV light are lost as a result of roughness-induced scattering. In this paper we present a novel approach for the roughness characterization of large EUV mirror optics based on light scattering measurements at a wavelength of 442 nm. The high sensitivity to roughness and the robustness of this method are exemplified for a 660 mm diameter collector mirror substrate. Area covering images of the high-spatial frequency roughness are retrieved which enable a detailed prediction of the EUV reflectance prior to coating. The results are compared to EUV reflectance measurements after coating.

Metrology on 3D features like line end gap in a SRAM structure is more challenging than on lines and spaces (L/S) structures. Scatterometry has been widely used on L/S structures and has enabled characterization of lithographic features providing with critical dimensions (CD) as well as feature height and side wall angle. In this paper, we will present the application of scatterometry to these challenging structures using an angle resolved polarized scatterometer: ASML YieldStar S-100. 3D features (line ends, brick walls,...) measurements will be presented. Measurement capability will be discussed in terms of sensitivity of the parameters of interest and correlation between them leading to a proper model choice.

The estimation of the impact of surface roughness on the light scattering losses and the scattering distribution is of crucial importance for deriving roughness specifications for optical surfaces. A detailed roughness analysis should always be based on surface Power Spectral Density functions and the band-limited roughness relevant for the application at hand. The scattering from single surfaces can easily be estimated using rather simple formulas. The most commonly used expression to estimate the total scattering, however, is only valid if the roughness is small and the correlation width is large compared to the wavelength of light. A special expression has been used in the thin film community for surface structures with short correlation lengths. It will be demonstrated that distinguishing between these limiting cases is unnecessary simply by using the concept of band-limited roughness. Different models are compared to results of scatter measurements and discussed with respect to their ranges of validity.

This paper presents the realization of the Isara 400 ultra-precision 3D coordinate measuring machine, which features a measuring volume of 400 × 400 × 100 mm and a traceable measurement uncertainty better than 50 nm. In order to achieve these challenging specifications, specific calibration strategies need to be applied, such as the calibration of the system's mirror table. In addition, a newly developed ultra-precision tactile probe system is described, featuring a probe tip radius of 35 μm; results of the 3D sensitivity calibration of this probe are presented. Finally, results are presented measuring a full hemisphere in 3D of a SiN ultra precision master ball, resulting in a repeatability of 7.9 nm rms.

In this paper we introduce a new optical technique for the measurement of aspheric and free-form optics and moulds. This technique, called confocal tracking, consists on tracking the focus on the sample while it is moved along the horizontal XY axes. Unlike all single-point based techniques, confocal tracking images the surface, which makes it possible to determine the best in focus position within every field of view and to correct the residual tracking errors for each measured point. As a result, confocal tracking provides shape measurements with nm-level accuracy and acquisition speeds of 1 mm/s typically. Depending on sample geometry, high NA objectives can be used, with which it is possible to measure slopes as high as 65°. In addition, because confocal tracking is not a single-point but an imaging technique, it is possible to center the surface to be measured with a very quick procedure that can be automated easily. This step may be particularly relevant for optics with symmetry of revolution. The confocal tracking profiler is a proprietary technology of UPC and Sensofar and can be considered the optical equivalent of a high-accuracy contact profiler.

Phase-shifting fringe projection is one of the most effective methods for shape measurement. Conventional systems are based on a projector imaging fringes into the measurement plane. These systems are mainly limited to the spectral range of visible light, as projectors in UV- or IR-range suffer from technical problems. However, for certain applications these spectral ranges can be of interest. We introduce a novel fringe projector based on beamshaping using a freeform mirror. The fringes in the measurement plane are generated by redistributing light with the freeform mirror. This projection system is wavelength-independent and highly energy efficient, which makes it suitable for applications in UV and IR spectral ranges. Additionally, a measurement field with axially very large dimension can be realized. We present here the system design as well as system simulation results, that demonstrate the principle of our novel approach.

Freeform surfaces enable innovative optics. They are not limited by axis symmetry and hence they are almost free in design. They are used to reduce the installation space and enhance the performance of optical elements. State of the art optical design tools are computing with powerful algorithms to simulate freeform surfaces. Even new mathematical approaches are under development /1/. In consequence, new optical designs /2/ are pushing the development of manufacturing processes consequently and novel types of datasets have to proceed through the process chain /3/. The complexity of these data is the huge challenge for the data handling. Because of the asymmetrical and 3-dimensional surfaces of freeforms, large data volumes have to be created, trimmed, extended and fitted. All these processes must be performed without losing the accuracy of the original design data. Additionally, manifold types of geometries results in different kinds of mathematical representations of freeform surfaces and furthermore the used CAD/CAM tools are dealing with a set of spatial transport formats. These are all reasons why manufacture-oriented approaches for the freeform data handling are not yet sufficiently developed. This paper suggests a classification of freeform surfaces based on the manufacturing methods which are offered by diamond machining. The different manufacturing technologies, ranging from servo-turning to shaping, require a differentiated approach for the data handling process. The usage of analytical descriptions in form of splines and polynomials as well as the application of discrete descriptions like point clouds is shown in relation to the previously made classification. Advantages and disadvantages of freeform representations are discussed. Aspects of the data handling in between different process steps are pointed out and suitable exchange formats for freeform data are proposed. The described approach offers the possibility for efficient data handling from optical design to systems in novel optics.

The aim of this work is to design an interferometric system that will adapt the shape of the reference wavefront to the shape of the measured optical surface. The designed adaptive two-beam interferometer uses the electromagnetic deformable mirror Mirao^TM52 from ImagineEyes for a generation of the reference wavefront and it can be applied for measurements of flat and spherical surfaces and even for measurements of free-form surfaces. We perform a detailed analysis of this technique and several possible measurement setups and principles of measurement and calibration of the designed adaptive interferometer are described. The principle of measurement is shown on an example of the experimental set-up of the adaptive interferometer in our laboratory.

With the growing number of complex-shaped lenses, aspheric and freeform surfaces, the demand for an appropriate and cost effective measurement technique to test these high quality components is still very high. Ferrofluid deformable mirrors (FDMs) offer a promising alternative. However, high accuracy profiles produced by FDMs have only been demonstrated in a closed-loop system which is inappropriate for metrology applications as it requires an additional measurement instrument and complicates the setup. Consequently, a FDM open-loop driving technique which maintains good precision while being simple, robust and stable, is required. In the following paper, we present a new active null test system based on a FDM for the testing of deep aspheric surfaces. We show a new driving method which provides an accurate open-loop operation mode of a FDM. We demonstrate that the method gives a significant improvement in comparison with the normalized influence function method. The results are promising enough to consider an active null test configuration for measuring optical components having high sag departures or complicated continuous profiles.

Fresnel lenses and other faceted or micro-optic devices are increasingly used in multiple applications like solar light concentrators and illumination devices. As applications are more exigent this characterization is of increasing importance. We present a technique to characterize the surface topography of optical surfaces. It is especially well adapted to Fresnel lenses where abrupt surface slopes are usually difficult to handle in conventional techniques. The method is based on a new photometric strategy able to codify the height information in terms of optical absorption in a liquid. A detailed topographic map is simple to acquire by capturing images of the surface. Some experimental results are presented. A single pixel height resolution of ~0.1 μm is achieved for a height range of ~50 μm. A surface slope analysis is also made achieving a resolution of ~±0.15°.

The evolution of astrophysical needs in the era of extremely large telescopes calls more and more complex instrumental systems and sub-systems. A promising solution would be to propose compact reflective optical systems, with less optical surfaces than classical optical designs. This is made possible if the designs are not limited by the use of known conics or symmetrical optical surfaces. Recent studies have shown that the use of highly aspherics could strongly reduce the number of optical surfaces and also the size of instruments, while improving the global system performances. The aim of this article is to study the feasibility of the design and manufacturing of highly aspheric optical mirrors, toward freeform mirrors, thanks to the combination of different active optics techniques: stress deformations up to plasticization phenomenon to provide the optical shape during the manufacturing and actuator corrections to compensate for residual errors during the operation phase of the instrument. A first step consists in structural mechanics analysis to understand as possible the non-linear behaviors of materials and its particular effects which depend on the material chosen, the global dimensions and the boundary conditions parameterized for the manufacturing process.

In order to carry out precise measurements of the thickness of a dielectric layer deposited on a metal surface two-dimensionally, we have introduced an ellipsometric measurement technique (EMT) to a new modified Otto configuration (MOC) that is used for observing surface plasmon resonance (SPR). In the conventional MOC, a planoconvex coupling singlet lens contacting with the planer air-metal interface at a one point was used, by which the SPR reflectance dip was formed as a two-dimensional circular fringe pattern. In the new MOC, in order to avoid the unnecessary physical contact between the dielectric layer and the lens, we inserted a thin air gap layer between them. In addition, we replaced the planoconvex lens by a cylindrical lens to enlarge the measurement area. By the cylindrical coupling lens, two parallel-straight-lined SPR dips were formed. On the locations of the two dips, we were able to carry out precise measurements of the thickness of the dielectric layer. We first measured the thickness of the Au layer basing on a fourlayer structure model: prism (BK7)-air-Au-substrate (BK7). Then we measured that of a TiO₂ layer deposited on the Au layer basing on a five-layer structure model: prism (BK7)-air-TiO₂-Au-substrate (BK7). We have proved experimentally that the combination of the EMT and the new MOC is effective for precise two-dimensional measurements of the thickness of the dielectric layer deposited on the metal surface.

LMJ and LIL are two French high power lasers dedicated to fusion and plasma experiments. These laser beams involve hundreds of rather large optical components, the clear aperture of the beams being 400×400 mm². Among these components, an adaptative mirror is used to correct wavefront distortions in the amplification section. A simple design has been chosen with push/pull actuators glued on the backside of a thin glass plate (9 mm). To ensure the bonding mechanical steadiness, we need enough roughness on this backside. That is why it is ground. We noticed figure instabilities on several of these ground backside substrates. Those wavefront distortions can be of several hundreds of nanometers. We designed a specific mount to avoid the possibility of measurement discrepancies due to mechanical mounting. We noticed then significant evolutions over a time-scale of a few months. The possibility of slow stress variations in the ground backside has then been considered. It has been known for a long time that a ground surface is in a compressive state and consequently tends to take a convex shape, this effect being named Twyman effect after its discoverer. Anyway, as far as we know, there is still doubt on the physical mechanisms involved and no publication has been made on the fluctuations of this effect. We wish to expose here results that led us to believe that instabilities are also linked to the external stress which is seen during transport or storage. Finally, we present the experiments we put in place on samples to improve our knowledge on this phenomenon and to test potential solutions.

LMJ and LIL are two French high power lasers dedicated to fusion and plasma experiments. These laser beams involve hundreds of large optical components, the clear aperture of the beams being 400×400 mm². In order to control the flatness requirements of its optics, the CEA has an 800 mm diameter Fizeau interferometer. Determining if optical components fulfil the very strict wavefront specifications can be difficult because these specifications can be equivalent to the defects of the reference flats of the interferometer. That is why we want to calibrate our reference flats in order to subtract their defects from the performed measurements. This absolute calibration is based on an iterative algorithm requiring three reference flats. In addition to the three basic combinations of the three flats, this method uses rotations and translations of one flat with respect to the others. First, we shall present a characterization of this method. The choice of different parameters, as the operations of translations and rotations required, will be discussed. Moreover, experimental errors have been introduced in the simulations and their limit values have been studied with regard to the other parameters. An application of this method on our three reference flats has been implemented over a 600 mm diameter. An absolute calibration requires a very precise implementation of the measurements and then we will see why data processing is necessary to reduce the residual shifts in translation but also in rotation and in zoom between the different measurements. Lastly, first uses of the absolute maps show a factor 5 to 10 improvement on the final accuracy.