This PDF file contains the front matter associated with SPIE Proceedings Volume 8884, including the Title Page, Copyright Information, Table of Contents, and the Conference Committee listing.

NASA requires technologies to fabricate and test optical components to accomplish its highest priority science missions. The NRC ASTRO2010 Decadal Survey states that an advanced large-aperture UVOIR telescope is required to enable the next generation of compelling astrophysics and exo-planet science; and, that present technology is not mature enough to affordably build and launch any potential UVOIR mission concept. The NRC 2012 NASA Space Technology Roadmaps and Priorities Report states that the highest priority technology in which NASA should invest to ‘Expand our understanding of Earth and the universe’ is next generation X-ray and UVOIR telescopes. Each of the Astrophysics division Program Office Annual Technology Reports (PATR) identifies specific technology needs. NASA has a variety of programs to fund enabling technology development: SBIR (Small Business Innovative Research); the ROSES APRA and SAT programs (Research Opportunities in Space and Earth Science; Astrophysics Research and Analysis program; Strategic Astrophysics Technology program); and several Office of the Chief Technologist (OCT) programs.

Sapphire poses very difficult challenges to optical manufacturers due to its high hardness and anisotropic properties. These challenges can result in long lead times and high prices. Large optical sensor windows demand much higher precision surfaces compared to transparent armor (windshields) to achieve acceptable image quality. Optimax is developing a high speed, cost effective process to produce such windows. The Optimax high speed process is a two-step process that combines precision fixed abrasive grinding and high speed polishing. In-house studies have demonstrated cycle time reduction of up to 6X as compared to conventional processing.

UltraForm Finishing (UFF) is a deterministic, subaperture, computer numerically controlled, grinding and polishing platform designed by OptiPro Systems. UFF is used to grind and polish a variety optics from simple spherical to fully freeform, and numerous materials from glasses to optical ceramics. The UFF system consists of an abrasive belt around a compliant wheel that rotates and contacts the part to remove material. This work aims to measure the stiffness variations in the system and how it can affect material removal rates. The stiffness of the entire system is evaluated using a triaxial load cell to measure forces and a capacitance sensor to measure deviations in height. Because the wheel is conformal and elastic, the shapes of contact areas are also of interest. For the scope of this work, the shape of the contact area is estimated via removal spot. The measured forces and removal spot area are directly related to material removal rate through Preston’s equation. Using our current testing apparatus, we will demonstrate stiffness measurements and contact areas for a single UFF belt during different states of its lifecycle and assess the material removal function from spot diagrams as a function of wear. This investigation will ultimately allow us to make better estimates of Preston’s coefficient and develop spot-morphing models in an effort to more accurately predict instantaneous material removal functions throughout the lifetime of a belt.

In 2012 a well-known company in the field of high precision optics assigned the University of Applied Sciences Deggendorf to determine a suitable parameter field for the active fluid jet polishing (AFJP) process in order to reach a surface accuracy of at least lambda / 5. The active fluid jet polishing is a relatively new and an affordable sub-aperture polishing process. For a fast and precise identification of the parameter field a considered design of experiment is necessary. The available control variables were the rotational speed of the nozzle, the distance between the test object and the jet, the feed rate, the material of the pin inside the nozzle and the material of the test object itself. In order to reach a significant data density on the one hand and to minimize the number of test runs on the other hand a meander shaped tool path was chosen. At each blank nine paths had been driven whereby at each path another parameter combination was picked. Thus with only one test object nine parameter settings may be evaluated. For the automatized analysis of the tracks a software tool was developed. The software evaluates ten sections which orthogonally intersect the nine tracks on the test-lens. The significant measurement parameters per section are the width and the height of each path as well as the surface roughness within the polished tracks. With the aid of these parameters and further statistical evaluations a suitable parameter field for the goal to find a constant and predictable removal spot was determined. Furthermore up to now over 60 test runs have been successfully finished with nine parameter combinations in each case. As a consequence a test evaluation by hand would be very time-consuming and the software facilitates it dramatically.

Magnetorheological finishing (MRF) of polycrystalline, chemical-vapor–deposited (CVD) zinc sulfide (ZnS) and zinc selenide (ZnSe) can leave millimeter-size artifacts on the part surface. These pebble-like features come from the anisotropic mechanical and chemical properties of the ceramic material and from the CVD growth process itself. The resulting surface texture limits the use of MRF for polishing aspheric and other complex shapes using these important infrared (IR) ceramics. An investigation of the individual contributions of chemistry and mechanics to polishing of other polycrystalline ceramics has been employed in the past to overcome similar material anisotropy problems. The approach taken was to study the removal process for the different single-crystal orientations that comprise the ceramic, making adjustments to mechanics (polishing abrasive type and concentration) and polishing slurry chemistry (primarily pH) to equalize the removal rate for all crystal orientations. Polishing with the modified slurry was shown to prevent the development of surface texture. Here we present mechanical (microhardness testing) and chemical (acid etching) studies performed on the four single-crystal orientations of ZnS: 100, 110, 111, and 311. We found that the (111) plane is 35% to 55% harder and 30% to 40% more resistant to chemical etching than the other three planes. This relatively high degree of variation in these properties can help to explain the surface texture developed from MRF of the polycrystalline material. Theoretical calculations of microhardness, planar, and bond densities are presented and compared with the experimental data. Here surface characterization of these single-crystal orientations of ZnS for material removal and roughness with chemically modified MR fluids at various pH levels between pH 4 and pH 6 are presented for the first time.

The manufacturing of structured molds calls for alternatives in terms of grinding wheel geometry and dressing. To manufacture geometric features in the micron range on molds, sharp edged fine grained grinding wheels can be used. A dressing procedure with metal alloy blocks is used to create sharp edged grinding wheels. This paper presents results and achieved tip radii of dressed resin bonded and metal bonded grinding wheels. Furthermore, a grinding test on a tungsten carbide mold is carried out to create a diffractive structure and the achieved form accuracy and surface roughness are presented.

The MegaJoule laser being constructed at the CEA near Bordeaux (France) is designed to focus more than 1 MJ of energy of UV light, on a millimeter scale target in the centre of an experiment chamber. After amplification and transport at the wavelength of 1053 nm, frequency conversion at 351 nm is done with KH₂PO₄ crystals. The final optic assembly of this system is made up of large fused silica optics, working in transmission, that are used to convey, focus or shape the laser beam. When exposed to fluences of some joules per square centimeter at 351 nm within nanosecond pulse duration, fused silica optics can exhibit localized damage. Damage sites grow exponentially after further laser exposition and therefore dramatically limit the optic lifetime. The nature of the surface finishing process has been established to determine the lifetime of these components under high UV fluences (i.e. more than 5 J/cm² for 3 ns pulses). Being able to reduce or eliminate the damage initiators such as subsurface cracks present in subsurface damage (SSD) layer of conventionally polished optical components aims this study. Magneto-rheological fluid finishing (MRF) is chosen as a final polishing tool to remove layers of material without inducing further damages. MRF enables to process optics with very small normal stresses applied to the surface during material removal and thus permits the elimination of the residual subsurface cracks. This study offers a better understanding of the efficiency of MRF polishing on the elimination of subsurface cracks in SSD layers.

High performance optical systems aiming for very low background noise from scattering or a sharp point spread function with high encircled energy often specify their beam wavefront quality in terms of a structure function or power spectral density function, which requires a control of mid-to-high spatial frequency surface errors during the optics manufacturing process. Especially for fabrication of large aspheric optics, achieving the required surface figure irregularities over the mid-to-high spatial frequency range becomes a challenging task as the polishing lap needs to be compliant enough to conform to the varying local surface shapes under the lap. This compliance degrades the lap’s smoothing capability, which relies on its rigidity. The smoothing effect corrects the mid-to-high spatial frequency errors as a polishing lap removes low spatial frequency (i.e. larger than the lap size) errors on the optical surface. Using a parametric smoothing model developed to quantitatively describe the smoothing effects during Computer Controlled Optical Surfacing (CCOS) processes, actual CCOS data from large aspheric optics fabrication projects have been analyzed and studied. The measured surface error maps were processed with the model to compare different polishing runs using various polishing parameters. The results showing the smoothing effects of mid-to-high spatial frequency surface irregularity will be presented to provide some insights for a CCOS process optimization in terms of smoothing efficiency.

Relationships between subsurface damage (SSD) depth and peak to valley surface roughness (Rt) have been widely studied and present a major interest for an easy assessment of the SSD depth. We seek the relation between SSD depth and other surface roughness parameters using the Abbott-Firestone curve on a large campaign of grinding tests (with different abrasive grain size, grinding speed and grinding mode). The results reveal that the Abbott-Firestone parameter Mr2, which can be linked to the volume fraction of valley in the roughness profile, is more accurate than Rt for an assessment of the SSD depth and that the relationship between Mr2 and the SSD depth varies when changing the grinding mode.

Classical mechano-chemical polishing is still a valuable technique, which gives unbeatable results for some types of optical surfaces. For example, optics for high power lasers requires minimized subsurface damage, very high cosmetic quality, and low mid spatial frequency error. One can hardly achieve this with use of subaperture polishing. The shape of the polishing tool plays a crucial role in achieving the required form of the optical surface. Often the shape of the polishing tool or pad is not known precisely enough during the manufacturing process. The tool shape is usually premachined and later is changed during the polishing procedure. An experienced worker could estimate the shape of the tool indirectly from the shape of the polished element, and that is why he can achieve the required shape in few reasonably long iterative steps. Therefore the lack of the exact tool shape knowledge is tolerated. Sometimes, this indirect method is not feasible even if small parts are considered. Moreover, if processes on machines like planetary (continuous) polishers are considered, the incorrect shape of the polishing pad could extend the polishing times extremely. Every iteration step takes hours. Even worse, polished piece could be wasted if the pad has a poor shape. The ability of the tool shape determination would be very valuable in those types of lengthy processes. It was our primary motivation to develop a contactless measurement method for large diffusive surfaces and demonstrate its usability. The proposed method is based on application of multiwavelength digital holographic interferometry with phase shift.

Grinding, polishing and finishing with ultra-precise form correction from one supplier. Satisloh provides machines, peripheral equipment, training, service, consumables, tools and process-support. All the equipment is made for industrial environment. Together with exclusive, experienced partners, aspheres will be manufactured more efficient.

Manufacturing aspheric optics can present challenges depending on the complexity of their shape. This is especially true during the finishing stage. To tackle this challenge, OptiPro Systems has developed two technologies for deterministic optical polishing: UltraForm Finishing (UFF) and UltraSmooth Finishing (USF). UFF is a deterministic sub aperture polishing process that polishes spherical, aspheric, and free form surface geometries. In contrast, the USF process is a deterministic mid to large size aperture polishing process that works with a conforming lap. These two technologies have the ability to tackle a wide range of optical shapes by removing sub-surface damage, removing various mid-spatial frequency artifacts that might be left from a grinding process, and correct the optic’s figure error in a controlled fashion. This presentation will describe these technologies, present performance information as to their capabilities, and show how OptiPro is developing these technologies to push the state of the art in manufacturing.

The increasing use of aspheres in a variety of optical systems has pushed the industry to become more efficient at its manufacturing processes. Non-optimized grinding techniques can cause excessive sub-surface damage and mid-spatial frequency errors which can be both time consuming and difficult to remove during polishing. The SCGa 100 grinder and SCPa 100 polisher provide unique platforms for asphere manufacturing. The SCGa 100 uses optimized kinematics to create a stiff and rigid platform which minimizes grinding errors and artifacts. Subsequently, polishing time on the SCPa 100 is decreased reducing the risk of altering the aspheric shape. This process improves surface quality while simplifying manufacturing.

Recent dramatic price volatility and assurance of supply concerns with cerium oxide have left many users of this material in an uncertain and vulnerable position. Since few viable alternatives to ceria for precision glass polishing exist, and much of the supply is very concentrated geographically, technology which conserves ceria, improves absolute removal rate and promotes slurry longevity becomes extremely attractive under these circumstances. Using a plasma-based process to produce cerium oxide confers some unique attributes to the particles which make them particularly well suited for precision glass polishing operations. Many of those same particle characteristics, such as full crystallinity, near theoretical density, very high surface and bulk purity and extremely high zeta potentials in water can also be useful in mitigating the risks associated with a limited and costly ceria supply. This paper will explore how plasma-derived particles, in combination with a high performance chemistry package, can together constitute a fully formulated precision glass polishing slurry with very high activity, extended slurry lifetime, ability to recycle, and excellent overall process economics. Results showing the effect of particle longevity and chemical additives on removal rate and process stability will be discussed in detail, and selected examples which distinguish the benefits of a fully formulated, plasma-derived cerium oxide polishing slurry over conventional milled ceria will be shown.

Optical systems that utilize complex optical geometries such as aspheres and freeform optics require precise control through the manufacturing process. As the preparatory stage for polishing, this is especially true for grinding. The quality of the grinding process can greatly influence the polishing process and the resultant finished product. OptiPro has performed extensive development work in evaluating components of a precision grinding machine to determine how they influence the overall manufacturing process. For example, spindle technology has a strong effect on how a grinding machine will perform. Through metrology techniques that measure the vibration characteristics of a machine and measurements of grinding forces with a dynamometer, OptiPro has also developed a detailed knowledge of how the machine can influence the grinding process. One of the outcomes of this work has led OptiPro to develop an ultrasonic head for their grinding platform to aid in reducing grinding forces. Initial results show a reduction in force by ~50%.

Additive manufacturing technologies have the ability to directly produce parts with complex geometries without the need for secondary processes, tooling or fixtures. This ability was used to produce concave lapping tools with a VFlash 3D printer from 3D Systems. The lapping tools were first designed in Creo Parametric with a defined constant radius and radial groove pattern. The models were converted to stereolithography files which the VFlash used in building the parts, layer by layer, from a UV curable resin. The tools were rotated at 60 rpm and used with 120 grit and 220 grit silicon carbide lapping paste to lap 0.750” diameter fused silica workpieces. The samples developed a matte appearance on the lapped surface that started as a ring at the edge of the workpiece and expanded to the center. This indicated that as material was removed, the workpiece radius was beginning to match the tool radius. The workpieces were then cleaned and lapped on a second tool (with equivalent geometry) using a 3000 grit corundum aluminum oxide lapping paste, until a near specular surface was achieved. By using lapping tools that have been additively manufactured, fused silica workpieces can be lapped to approach a specified convex geometry. This approach may enable more rapid lapping of near net shape workpieces that minimize the material removal required by subsequent polishing. This research may also enable development of new lapping tool geometry and groove patterns for improved loose abrasive finishing.

Recently, the desire to use freeform optics has been increasing. Freeform optics can be used to expand the capabilities of optical systems. These same traits that give freeform optics the ability to improve optical systems, also makes them more challenging to manufacture. This holds true for grinding, polishing, and metrology, and, as freeform optics become more prevalent in the industry, tolerances will become more stringent. OptiPro Systems has developed a method of deterministic freeform polishing to be used with its UltraForm Finishing (UFF) process. This method uses the error map of the surface to determine the appropriate feed rates for removing a portion of the error from the surface of the optic. The material removed varies across the surface of the optic to allow for the error to decrease across the surface at a uniform rate. The flexibility of this method allows for the deterministic polishing of surfaces that can be mathematically modeled. In addition to deterministic polishing, OptiPro is also developing a software package for generating freeform tool paths. This software can be used for both grinding and polishing freeform optics. It has the ability to generate the freeform tool paths for deterministic polishing. This software will make is easier to manufacture and polish complex freeform surfaces.

For over 100 years, optical imaging systems were limited to rotationally symmetric lens elements, due to limitations in processing optics. However, the present rapid development and application of CNC machines has made fabrication of non-rotationally symmetric lenses, such as freeform surfaces, economical. The benefit of using freeform surfaces is that the lens designer has more flexibility to create innovative 3D imaging packages, while correcting for aberrations. This report details capabilities at Optimax for manufacturing freeform surfaces, with a specific example towards creation of freeform ZnS-multispectral optics for application as a corrector element. In addition to fabricating freeform optics, advances have been made in producing smooth surfaces on polycrystalline materials. In the past, achieving a smooth surface on polycrystalline materials during sub-aperture polishing has proven challenging, because of a phenomenon called grain highlighting. Significant progress has been made at Optimax in this field through utilization of proprietary pads, slurries, and processes.

Innovative freeform optical systems such as head-up displays or LED headlights often require high quality and high volume optics. Injection molded polymer optics offer a cost effective solution. However, mold manufacturing for this process is extremely challenging as the machining of freeform surfaces is currently characterized by several independent production steps which can limit surface accuracy. By integrating diamond turning, milling, and metrology onto a single platform, the UPC 400 improves surface accuracy. Advanced software for machining and measurement data further reduces surface inaccuracies. This combination makes the UPC 400 efficient for prototyping free-form optics and manufacturing high precision molds.

Ultra precision diamond turning of hardened steel to produce optical quality surfaces can be realized by applying an ultrasonic assisted process. With this technology optical moulds used typically for injection moulding can be machined directly from steel without the requirement to overcoat the mould with a diamond machinable material such as Nickel Phosphor. This has both the advantage of increasing the mould tool lifetime and also reducing manufacture costs by dispensing with the relatively expensive plating process. This publication will present results we have obtained for generating free form moulds in hardened steel by means of ultrasonic assisted diamond turning with a vibration frequency of 80 kHz. To provide a baseline with which to characterize the system performance we perform plane cutting experiments on different steel alloys with different compositions. The baseline machining results provides us information on the surface roughness and on tool wear caused during machining and we relate these to material composition. Moving on to freeform surfaces, we will present a theoretical background to define the machine program parameters for generating free forms by applying slow slide servo machining techniques. A solution for optimal part generation is introduced which forms the basis for the freeform machining experiments. The entire process chain, from the raw material through to ultra precision machining is presented, with emphasis on maintaining surface alignment when moving a component from CNC pre-machining to final machining using ultrasonic assisted diamond turning. The free form moulds are qualified on the basis of the surface roughness measurements and a form error map comparing the machined surface with the originally defined surface. These experiments demonstrate the feasibility of efficient free form machining applying ultrasonic assisted diamond turning of hardened steel.

Conformal windows pose new and unique challenges to manufacturing due to the shape, measurement of, and requested hard polycrystalline materials. Their non-rotationally symmetric shape and high departure surfaces do not lend themselves to traditional optical fabrication processes. The hard crystalline materials are another challenge due to increased processing time and possibility of grain decoration. We have developed and demonstrated a process for manufacturing various conformal windows out of fused silica, glass, zinc-sulfide multispectral, and spinel. The current process involves CNC generation/grinding, VIBE polishing, and sub-aperture figure correction. The CNC generation step incorporates an ultrasonic assisted grinding machine; the machine settings and tool are being continuously optimized for minimal sub-surface damage and surface form error. In VIBE, polishing to less than 5 nm rms surface roughness while maintaining overall form error is accomplished with a full aperture conformal polishing tool and with rapid removal rates. The final sub-aperture polishing step corrects the overall form error. Currently we utilize our CMM for surface form measurement and have shown that we can produce spinel conformal windows with form error within ±10 micrometers of the nominal shape, without grain decoration. This conformal window manufacturing process is continuously optimized for cost reduction and precision of the final optic.

The fabrication of complex shaped metal mirrors for optical imaging is a classical application area of diamond machining techniques. Aspherical and freeform shaped optical components up to several 100 mm in diameter can be manufactured with high precision in an acceptable amount of time. However, applications are naturally limited to the infrared spectral region due to scatter losses for shorter wavelengths as a result of the remaining periodic diamond turning structure. Achieving diffraction limited performance in the visible spectrum demands for the application of additional polishing steps. Magnetorheological Finishing (MRF) is a powerful tool to improve figure and finish of complex shaped optics at the same time in a single processing step. The application of MRF as a figuring tool for precise metal mirrors is a nontrivial task since the technology was primarily developed for figuring and finishing a variety of other optical materials, such as glasses or glass ceramics. In the presented work, MRF is used as a figuring tool for diamond turned aluminum lightweight mirrors with electroless nickel plating. It is applied as a direct follow-up process after diamond machining of the mirrors. A high precision measurement setup, composed of an interferometer and an advanced Computer Generated Hologram with additional alignment features, allows for precise metrology of the freeform shaped optics in short measuring cycles. Shape deviations less than 150 nm PV / 20 nm rms are achieved reliably for freeform mirrors with apertures of more than 300 mm. Characterization of removable and induced spatial frequencies is carried out by investigating the Power Spectral Density.

In interferometric testing of surfaces a major task is to avoid the introduction of aberrations due to misalignment of the surface under test (SUT). An automated method for the positioning of aspheric and free-form surfaces in a non-null test interferometer, as well as a method for the distinction between alignment introduced aberrations and surface errors is presented. A combination of both methods allows for a fully automated alignment with low accuracy requirements concerning the positioning stage. In this work the method for the alignment as well as the alignment error correction is presented and the misalignment introduced measurement uncertainties are estimated. Simulation results as well as experimental results showing the feasibility of the method are presented.

Metrology of asphere surfaces is critical in the precision optics industry. Surface metrology serves as feedback into deterministic grinding and polishing platforms. Many different techniques and devices are used to qualify an asphere surface during fabrication. A contact profilometer is one of the most common measurement technologies used in asphere manufacturing. A profilometer uses a fine stylus to drag a diamond or ruby tip over the surface, resulting in a high resolution curved profile. Coordinate measuring machines (CMM) apply a similar concept by touching the optic with a ruby or silicon carbine sphere. A CMM is able to move in three dimensions while collecting data points along the asphere surface. Optical interferometers use a helium-neon laser with transmission spheres to compare a reflected wavefront from an asphere surface to a reference spherical wavefront. Large departure aspheres can be measured when a computer generated hologram (CGH) is introduced between the interferometer and the optic. OptiPro Systems has developed a non-contact CMM called UltraSurf. It utilizes a single point non-contact sensor, and high accuracy air bearings. Several different commercial non-contact sensors have been integrated, allowing for the flexibility to measure a variety of surfaces and materials. Metrology of a sphere and an asphere using a profilometer, CMM, Interferometer with a CGH, and the UltraSurf will be presented. Cross-correlation of the measured surface error magnitude and shape will be demonstrated. Comparisons between the techniques and devices will be also presented with attention to accuracy, repeatability, and overall measurement time.

A non-contact optical scanning metrology solution measuring aspheric surfaces is presented, which is based on multi wavelength interferometry (MWLI). The technology yields high density 3D data in short measurement times (including set up time) and provides high, reproducible form measurement accuracy. It measures any asphere without restrictions in terms of spherical departures. In addition, measurement of a large variety of special optics is enabled, such as annular lenses, segmented optics, optics with diffractive steps, ground optics, optics made of opaque and transparent materials, and small and thin optics (e.g. smart phone lenses). The measurement instrument can be used under production conditions.

The design of an interferometer workstation for the testing of large concave and convex spherical optics is presented. The workstation handles optical components and mounts up to 425 mm in diameter with mass of up to 40 kg with 6 axes of adjustment. A unique method for the implementation of focus, roll and pitch was used allowing for extremely precise adjustment. The completed system includes transmission spheres with f-numbers from f/1.6 to f/0.82 incorporating reference surface diameters of up to 306 mm and surface accuracies of better than 63 nm PVr. The design challenges and resulting solutions are discussed. System performance results are presented.

Fizeau type phase measuring interferometers are widely used in the optics industry for surface metrology. Measurement of spherical surfaces requires the use of transmission spheres which are commercially available in various F-numbers. A basic assumption of Fizeau interferometry is that the light reflected off the reference surface, called the reference beam, and the light reflected off the surface being tested, called the test beam, follow a common path back through the optics. For this to be strictly true, we would need the surface being tested to be perfectly spherical and positioned exactly concentric with the reference surface. Measurement inaccuracy that results from failure to meet this condition is referred to as retrace error. Retrace error has been largely ignored with regard to testing nominally spherical surfaces, yet it can be significant when high test accuracy is needed. In this paper, the author identifies two types of retrace error resulting from the test setup: Axial; induced spherical aberration resulting from defocus, and Transverse; induced coma as a result of tilt. The magnitude and exact form of retrace error is shown to be a function of the optical design of the transmission sphere. It is shown that, for the most part, measurement accuracy is independent of the transmitted wavefront error of the transmission sphere. It is shown that retrace error can be modeled in a lens design program with excellent agreement to measurement data. Specific design examples will be presented, including improvements to minimize retrace error. The significance of retrace error to the test accuracy of both spherical and aspheric surfaces will be discussed.

We have performed a round-robin study of surface irregularity measurements of a free-form toroidal window. The measurement tools were a Leitz scanning CMM at Optimax Systems, Inc., an UltraSurf, a non-contact measuring system at OptiPro Systems, a Zeiss scanning CMM at OptiPro Systems, a F25 micro-CMM at Carl Zeiss Industrial Metrology, and an ASI(Q)™ at QED Technologies. Each instrument resulted in a 2.5D surface error map. The measurements were compared with multiple analysis settings. The different analysis settings removed some low frequency height errors, which varied amongst the measurements. This highlights the need for more study to determine the reasons for the differences in the low frequency errors. With the low frequency errors removed, the measurements compared very well, to within 0.2 μm rms.

Arithmetic averaging of interferometric phase measurements is a well-established method for reducing the effects of time varying disturbances, such as air turbulence and vibration. Calculating a map of the standard deviation for each pixel in the average map can provide a useful estimate of its variability. However, phase maps of complex and/or high density fringe fields frequently contain defects that severely impair the effectiveness of simple phase averaging and bias the variability estimate. These defects include large or small-area phase unwrapping artifacts, large alignment components, and voids that change in number, location, or size. Inclusion of a single phase map with a large area defect into the average is usually sufficient to spoil the entire result. Small-area phase unwrapping and void defects may not render the average map metrologically useless, but they pessimistically bias the variance estimate for the overwhelming majority of the data. We present an algorithm that obtains phase average and variance estimates that are robust against both large and small-area phase defects. It identifies and rejects phase maps containing large area voids or unwrapping artifacts. It also identifies and prunes the unreliable areas of otherwise useful phase maps, and removes the effect of alignment drift from the variance estimate. The algorithm has several run-time adjustable parameters to adjust the rejection criteria for bad data. However, a single nominal setting has been effective over a wide range of conditions. This enhanced averaging algorithm can be efficiently integrated with the phase map acquisition process to minimize the number of phase samples required to approach the practical noise floor of the metrology environment.

High-precision optical elements are used in various fields. Ultraprecise aspherical mirrors that offer nanofocusing and high coherence are used to concentrate high-brightness X-rays in developing third-generation synchrotron radiation facilities. In industry, extreme ultraviolet (wavelength: 13.5 nm) lithography, which is used to fabricate semiconductor devices, uses high-accuracy aspherical mirrors for its projection optical systems. The demand for rapid progress in nanomeasurement technologies is increasing because it is difficult to realize next-generation ultraprecise mirrors with the required precision by conventional processing. The measuring method itself requires superhigh precision. We developed an innovative nanoprofiler that can directly measure the figure of high-accuracy mirrors without using a reference surface. The principle of our measuring method is to determine the normal vectors by causing the optical paths of the incident and reflected light at the measurement point to coincide; it is based on the straightness of laser light and the accuracy of rotational goniometers. From the acquired normal vectors and their coordinates, the three-dimensional shape is calculated by a reconstruction algorithm. We measured concave spherical mirrors and compared the results with those using a Fizeau interferometer. The profiles of the mirrors were consistent within the range of error in their middle portions. In addition, we evaluated the performance of an airflow control unit by measuring a concave spherical mirror. This unit suppressed the influence of environmental change, and drastically improved the repeatability.

Freeform applications are growing and include helmet-mounted displays, conformal optics (e.g. windows integrated into airplane wings), and those requiring the extreme precision of EUV. These non-rotationally symmetric surfaces pose challenges to optical fabrication, mostly in the areas of polishing and metrology. The varying curvature of freeform surfaces drives the need for smaller, more “conformal”, tools for polishing and reference beams for interferometry. In this paper, we present fabrication results of a high-precision freeform surface. We will discuss the total manufacturing process, including generation, pre-polishing, MRF^®, and metrology, highlighting the capabilities available in today’s optical fabrication companies.

The modern optical industry requires objects with complex topographical structures. Free-form shaped objects are of large interest in many branches, especially for size reduced, modern lifestyle products like digital cameras. State of the art multi-axes-coordinate measurement machines (CMM), like the topographical measurement machine TII-3D, are by principle suitable to measure free-form shaped objects. The only limitation is the software package. This paper may illustrate a simple way to enhance coordinate measurement machines in order to add a free-form function. Next to a coordinate measurement machine, only a state of the art CAD^† system and a simple piece of software are necessary. For this paper, the CAD software CREO^‡ had been used. CREO enables the user to develop a 3D object in two different ways. With the first method, the user might design the shape by drawing one or more 2D sketches and put an envelope around. Using the second method, the user could define one or more formulas in the editor to describe the favoured surface. Both procedures lead to the required three-dimensional shape. However, further features of CREO enable the user to export the XYZ-coordinates of the created surface. A special designed software tool, developed with Matlab^§, converts the XYZ-file into a measurement matrix which can be used as a reference file. Finally the result of the free-form measurement, carried out with a CMM, has to be loaded into the software tool and both files will be computed. The result is an error profile which provides the deviation between the measurement and the target-geometry.

We present an imaging technique for the 3D-form metrology of optical surfaces. It is based on the optical absorption in fluids situated between the surface and a reference. An improved setup with a bi-chromatic light source is fundamental to obtain reliable topographic maps. It is able to measure any surface finish (rough or polished), form and slope and independently of scale. We present results focused on flat and spherical optical surfaces, arrays of lenses and with different surface finish (rough-polished). We achieve form accuracies from several nanometers to sub-lambda for sag departures from tens to hundred of microns. Therefore, it seems suitable for the quality control in the production of precision aspheric, freeform lenses and other complex shapes on transparent substrates, independently of the surface finish.

We present an optical method for free-form mirrors qualification developed by the Italian National Institute for Astrophysics (INAF) in the context of the ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana) Project which includes, among its items, the design, development and installation of a dual-mirror telescope prototype for the Cherenkov Telescope Array (CTA) observatory. The primary mirror panels of the telescope prototype are free-form concave mirrors with few microns accuracy required on the shape error. The developed technique is based on the synergy between a Ronchi-like optical test performed on the reflecting surface and the image, obtained by means of the TraceIT ray-tracing proprietary code, a perfect optics should generate in the same configuration. This deflectometry test allows the reconstruction of the slope error map that the TraceIT code can process to evaluate the measured mirror optical performance at the telescope focus. The advantages of the proposed method is that it substitutes the use of 3D coordinates measuring machine reducing production time and costs and offering the possibility to evaluate on-site the mirror image quality at the focus. In this paper we report the measuring concept and compare the obtained results to the similar ones obtained processing the shape error acquired by means of a 3D coordinates measuring machine.

This study explores the structural relaxation behavior of As₂Se₃ by thermo mechanical analysis in order to characterize and eventually predict volume change in As₂Se₃ upon relaxation during cooling after precision glass molding (PGM) and annealing. A vertical beam of As₂Se₃ was placed in a thermo mechanical analyzer (TMA) and fully relaxed at a given temperature. The temperature was then quickly changed a given amount and the 1-D relaxation of the beam was measured until it reached equilibrium at the new temperature. The resultant curve was then fit with a Prony series which captured the relaxation data. The mathematical representation of the relaxation is then analyzed as a function of time, temperature, and quench rate and can be used to predict one dimensional (1-D) length change upon relaxation. A maximum of three terms is needed to describe the relaxation behavior and that number declines with an increase in temperature. This decay of the number of Prony terms needed to describe relaxation points to a structure that relaxes with less complexity as it approaches T_g. These trends can be converted to 3-D due to the amorphous and therefore typically isotropic nature of As₂Se₃ glass. This volume change information as a function of vital processing parameters can then be used to predict the change in shape of a work piece during cooling or post process annealing within a precision molding cycle. The mathematical representation of volume relaxation can then be applied to finite element models (FEM) of As₂Se₃ lenses or other optical elements.

The structural and optical properties of AsSe chalcogenide glass, starting with As40Se60, were studied as a function of Ge or Se additions. These elements provide broad glass forming options when combined with the host matrix to allow for compositional tuning of properties. Optimization of glass composition has been shown to produce bulk glasses with a thermoptic coefficient (dn/dT) equal to zero, as well as a composition which could demonstrate a net zero change in index after precision glass molding (PGM). The bulk glass density, coefficient of thermal expansion (CTE), refractive index, and dn/dT were measured for all bulk compositions, as was the refractive index after PGM. For the bulk glasses examined, both the refractive index (measured at discrete laser wavelengths from 3.4 to10.6 μm) and dn/dT were observed to decrease as the molecular percentage of either Ge or Se is increased. Compared to the starting glass’ network, additions of either Ge or Se lead to a deviation from the “optimally constrained” binary glass’ average coordination number <r> = 2.4. Additions of Se or Ge serve to decrease or increase the average coordination number (CN) of the glass, respectively, while also changing the network’s polarizability. After a representative PGM process, glasses exhibited an “index drop” consistent with that seen for oxide glasses.¹ Based on our evaluation, both the Gecontaining and Ge-free tielines show potential for developing unique compositions with either a zero dn/dT for the unmolded, bulk glass, as well as the potential for a glass that demonstrates a net zero “index drop” after molding. Such correlation of glass chemistry, network, physical and optical properties will enable the tailoring of novel compositions suitable for prototyping towards targeted molding behavior and final properties.

SP-100 from Satisloh is the perfect coating machine for application in precision optics. Thanks to its innovative concept SP-100 can coat materials in a range of refraction indexes from 1.47 up to 2.05 in the visible (with all the intermediate indexes in between) and up to n=3.5 in the infrared by using only one target material. SP-100 is well suitable for application in the field of microscopy, laser optics, watches, optical filters, endoscopy, semiconductors and more. By replacing the target material the application range of the machine can be further extended. SP-100 is based on the reliable reactive bipolar Direct Current (DC) pulsed magnetron sputtering technology which guarantees high density of the deposited species, low stress of the deposited multilayer film, high reproducibility, very high hardness (up to 1200 Vickers hardness) with unbeatable high rates ideal for industrial applications. DC-pulsed sputtering assure less arc events and a lower heat load than Radio Frequency (RF) sputtering making SP-100 suitable for different substrates material and for cemented lenses. The small chamber of the SP-100 ensures very fast processes and a broadband AR can be coated in less than 15 minutes process time door to door. Thanks to its flexible substrate holder SP-100 can hold lenses of different sizes and shapes: from small size optics up to 100 mm diameter lenses, rod lenses up to 50 mm length or even glass fibers.

For many years Gooch and Housego have been supplying very high laser induced damage threshold coated parts to projects such as the National Ignition Facility. We have optimised our substrate preparation and coating processes to achieve repeatable performance well in excess of 10Jcm^-2, 1064nm 3ns pulses. This has used electron beam deposition technology. While this has performed well in the controlled environments of the science labs, it is well known that the coatings produced are porous and therefore susceptible to absorbing water and other chemicals from the atmosphere, modifying the coating performance. The traditional solution has been to select ion beam sputtering deposition techniques, but these are typically expensive, with smaller capacity chambers and produce high stress coatings. Therefore they are not optimal for higher volume components and thin substrates. We present the results of our development to optimise an ion-assisted deposition technique offering the possibility of trading off various design parameters including coating porosity and laser damage threshold, to optimise the coating performance of optics located where they can suffer contamination and outgassing. The coatings can be deposited in a large chamber at reasonable speeds suited to higher volume throughputs. Such coatings include the challenging design of a dual band visible and 1064nm optimised for both visible transmission range and LIDT performance at 1064nm.

Pulsed DC reactive sputtering is a very interesting technique for coating applications. Reactive sputtering can give very dense layers, low stress of the deposited multilayer film, high reproducibility, very high hardness (up to 1200 Vickers hardness) with unbeatable high rates ideal for industrial applications. SP-100 is Satisloh reactive sputtering systems with only one target material but can deposit various film materials simply by using different gases such as argon, as well as the reactive gases nitrogen and oxygen. Silicon-oxides, silicon-nitrides and all kinds of silicon-oxy-nitrides (SiO_x-Si_xO_yN_z-Si_xN_y) with a refractive index range of 1.44-2.05 in the visible range can be obtained. In the reactive sputtering the material it is usually deposited in the so called “transition mode” where it must be found the correct equilibrium point between the target voltage and the reactive gas flow. The transition mode assures a dense film with a stable rate. Condition to find such equilibrium point is given by the so called “material hysteresis” in which the target voltage is depicted in function of the reactive gas voltage. The hysteresis and the consequent equilibrium point are strongly depended by the power supplied to the target and the inert gas (argon) flow which could affect the optical characteristics and the deposition rate. We checked the refractive indexes of the SiO_x and Si_xN_y of very thin (1 QW Optical thickness at 520 nm) and thicker (3, 5 and 9 QW @520 nm) reporting how the different conditions can affect the refractive index and the deposition rate of the different materials.

Gradient-orthogonal representations of aspheric shapes give a more effective and intuitive characterization that also copes with increasingly complex surfaces. Further, we have seen a range of applications where standard design codes (including CodeV® and Zemax®) can find systems with better optical performance when optimized in this representation. The examples presented here include a system with no global axis of symmetry and another with freeform surfaces. In all these particular cases, the end results can be retro-fitted in terms of conventional representations, but the optimizers fail to find the superior solutions unless an orthogonal basis is employed during the design process. Because the communication of shape is so much more effective in terms of a gradient-orthogonal description, our results give added motivation for the communities of design, fabrication, and testing to gain more experience with this new convention.

Aspheric surfaces provide significant benefits to an optical design. Unfortunately, aspheres are usually more difficult to fabricate than spherical surfaces, making the choice of whether and when to use aspheres in a design less obvious. Much of the difficulty comes from obtaining aspheric measurements with comparable quality and simplicity to spherical measurements. Subaperture stitching can provide a flexible and effective test for many aspheric shapes, enabling more cost-effective manufacture of high-precision aspheres. To take full advantage of this flexible testing capability, however, the designer must know what the limitations of the measurement are, so that the asphere designs can be optimized for both performance and manufacturability. In practice, this can be quite difficult, as instrument capabilities are difficult to quantify absolutely, and standard asphere polynomial coefficients are difficult to interpret. The slope-orthogonal “Q” polynomial representation for an aspheric surface is ideal for constraining the slope departure of aspheres. We present a method of estimating whether an asphere described by Q polynomials is measurable by QED Technologies’ SSI-A system. This estimation function quickly computes the testability from the asphere’s prescription (Q polynomial coefficients, radius of curvature, and aperture size), and is thus suitable for employing in lens design merit functions. We compare the estimates against actual SSI-A lattices. Finally, we explore the speed and utility of the method in a lens design study.

When building high-performance camera lenses, it is often preferable to tailor element-to-element air spaces instead of tightening the fabrication tolerances sufficiently so that random assembly is possible. A tailored air space solution is usually unique for each serial number camera lens and results in nearly nominal performance. When these air spaces are computed based on measured radii, thickness, and refractive indices, this can put a strain on the design engineering department to deal with all the data in a timely fashion. Excel^† may be used by the assembly technician as a preprocessor tool to facilitate data entry and organization, and to perform the optimization using CODE V^‡ (or equivalent) without any training or experience in using lens design software. This makes it unnecessary to involve design engineering for each lens serial number, sometimes waiting in their work queue. In addition, Excel can be programmed to run CODE V in such a way that discrete shim thicknesses result. This makes it possible for each tailored air space solution to be achieved using a finite number of shims that differ in thickness by a reasonable amount. It is generally not necessary to tailor the air spaces in each lens to the micron level to achieve nearly nominal performance.

Efficient and reliable optical design requires knowledge of the production chain, the materials used, and the environmental circumstances in the field of operation. This is realized in the comprehensive modelling approach consisting of three steps: • Design for manufacturing, i.e. the model must be adjusted to the process chain. Knowledge of design rules is required. • Robust design, i.e. optimization of the functional design with the objective of a compensation of the tolerance influences on the system’s performance. Knowledge of the tolerances of the individual process steps is required. • Reliable design with respect to environmental and operational effects, respectively. Coupling of an optical and mechanical simulation tool is required to form the optical simulation environment. The availability of process knowledge such as e.g. design rules and manufacturing tolerances is ensured by coupling of the optical simulation environment with a process knowledge database. Integration of measured surface data in this simulation environment enables a realistic simulation and analysis of real, manufactured optics. This approach allows e.g. for the evaluation of replication methods such as precision molding or injection molding against high-precision manufacturing methods, e.g. diamond turning.

Design of LED optical elements producing uniform illumination in rectangular regions is one of the most actual and challenging problems in development of lighting devices. As a rule, LED optical element has at least two surfaces (inner and outer) that leads to computational complexity of design process and requires application of different optimization techniques. We present a new rapid computational method for automatical design of optical elements with two free-form surfaces which generate uniform irradiance distribution in the rectangular region. Such optical elements have high lighting efficiency (about 92 %) and can be produced by injection molding.

We propose a novel method of designing a refractive surface to generate a line-shaped directivity diagram represented as a vector function of one argument. A general relationship for the refractive surface is derived as an envelope of a parametric family of ellipsoids or hyperboloids of revolution (depending on the relative refractive index of the media separated by the surface). Each surface in the family transforms the incident spherical beam from a point (compact) light source into a beam with plane wavefront of desired direction. Optical elements generating line segment directivity diagram, circular arc directivity diagram and two-arc composite directivity diagram are designed. The simulation results demonstrate the generation of high-quality diagrams.

An optical metrology laboratory has been developed to characterize the optical properties of optical window materials to be used for aerospace applications. Several optical measurement systems have been selected and developed to measure spectral transmittance, haze, clarity, birefringence, striae, wavefront quality, and wedge. In addition to silica based glasses, several optical lightweight polymer materials and transparent ceramics have been investigated in the laboratory. The measurement systems and selected empirical results for non-silica materials are described. These measurements will be used to form the basis of acceptance criteria for selection of window materials for future aerospace vehicle and habitat designs.

There are no calibration standards currently available for metrology equipment used to measure spherical aberration. We have selected a set of plano-convex lenses that can be used as spherical aberration calibration standards. The key parameters of the lenses were measured using a nodal optical bench and a low coherence interferometer. Spherical aberrations of the lenses were measured using a commercially available aberrometer the CrystalWave™, based on a Shack-Hartmann wavefront sensor. The lenses were then modeled in optical modeling software, where the spherical curvatures of the lenses were adjusted to match the key parameters. The measured spherical aberrations were then compared to the values provided by the modeling software.

We have developed a procedure for precise measurement of the group refractive index for materials in air and liquid environments, using a low coherence interferometer. For example, in manufacturing of soft contact lenses, the lenses are always kept hydrated in a saline solution. Knowing accurate refractive index of the lens is important to metrology and quality control purposes. The small refractive index difference between the liquid and the lens makes such tasks especially challenging. The developed procedure allows us to obtain measurement repeatability for group refractive index less than 1 x 10^-3 for materials with thicknesses on the order of 100 microns, when measured in liquid. The measurement repeatability further improves for measurements in air, or for thicker materials.

Thales Angénieux (TAGX) designs and manufactures zoom lens assemblies for cinema applications. These objectives are made of mobile lens assemblies. These need to be precisely characterized to detect alignment, polishing or glass index homogeneity errors, which amplitude may range to a few hundreds of nanometers. However these assemblies are highly aberrated with mainly spherical aberration (>30 μm PV). PHASICS and TAGX developed a solution based on the use of a PHASICS SID4HR wave front sensor. This is based on quadri-wave lateral shearing interferometry, a technology known for its high dynamic range. A 100-mm diameter He:Ne source illuminates the lens assembly entrance pupil. The transmitted wave front is then directly measured by the SID4- HR. The measured wave front (WF_meas) is then compared to a simulation from the lens sub-assembly optical design (WF_design). We obtain a residual wave front error (WF_manufactured), which reveals lens imperfections due to its manufacturing. WF_meas=WF_design+(WFE_radius+WFE_glass+WFE_polish)=WF _design + WF_manufactured The optical test bench was designed so that this residual wave front is measured with a precision below 100 nm PV. The measurement of fast F-Number lenses (F/2) with aberrations up to 30 μm, with a precision of 100 nm PV was demonstrated. This bench detects mismatches in sub-assemblies before the final integration step in the zoom. Pre-alignment is also performed in order to overpass the mechanical tolerances. This facilitates the completed zoom alignment. In final, productivity gains are expected due to alignment and mounting time savings.

Large mirrors are required for a wide variety of applications. Two key constraints are mirror stability and mirror mass. Low expansion glass ceramics remain a useful material because of its excellent thermal stability, relative ease of processing and lower cost compared to alternatives. However there is room for the improvement of the manufacturing techniques over the traditional methods of milling and etching, which are high risk, expensive and time consuming. A solid blank is milled out using high speed diamond tooling to leave fragile webs of supporting material. The final process steps are the highest risk, when it is possible for catastrophic flaws to appear. We present a novel method of producing a monolithic structure from component pieces that provide a lower risk, lower cost method of producing stable and light-weighted mirrors. Individual smaller components are machined and then bonded together. The bonding process results in near substrate strength components without compromising the very low thermal expansion of the glass ceramic. It also allows the creation of novel designs with hollow cavities embedded within the structure. Prior to commencing the fabrication the mechanical design was modelled to predict the stability of candidate designs. Tests were carried out on witness pieces to prove the relative strength of the bonds. Prototypes were then fabricated and tested for thermal stability.

In display or semiconductor manufacturing it is a constant drive towards the use of scale effects to reduce costs per unit. For equipment suppliers this leads to ever bigger optical components. To answer this need new cost-efficient technologies are required. In the process chain, the polishing step is one of the most important as it defines the optical surface. In this work the polishing step of a planar surface of a cylindrical component is investigated. A simulation for long scanning optics starting from Preston equation has been derived. By separating the optical surface into several zones, velocity variable polishing paths have been computed. Including pressure differences at the edges so called removal maps have been plotted. At the end, it has been verified that the model approach is able to influence polishing results of meter size optics by velocity controlled polishing.

The Astronomical Observatory of Brera (INAF-OAB, Italy), with the financing support of the European Space Agency (ESA), has concluded a study regarding a glass shaping technology for the production of grazing incidence segmented x-ray optics. This technique uses a hot slumping phase, in which pressure is actively applied on thin glass foils being shaped, to form a cylindrical approximation of Wolter I x-ray segments, and a subsequent cold slumping phase, in which the final Wolter I profile is then freeze into the glass segments during their integration in elemental X-ray Optical Units. The final goal of this study was the manufacturing of a prototype containing a number of slumped pair plates (meaning parabola and hyperbola couples) having representative dimensions to be tested both in UV light and in x-rays at the Panter facility (Germany). In this paper, the INAF-OAB slumping technique, comprising a shaping step and an integration step is described, together with the results obtained on the manufactured prototype modules: the first prototype was aimed to test the ad-hoc designed and built semi-automatic Integration MAchine (IMA) and debug its control software. The most complete module comprises 40 slumped segments of Schott D263 glass type of dimension 200 mm x 200 mm and thickness of 0.4 mm, slumped on Zerodur K20 mould and stacked together through glued BK7 glass structural ribs to form the first entire x-ray optical module ever built totally composed by glass. A last prototype was aimed at demonstrate the use of Schott glass AF32 type instead of D263. In particular, a new hot slumping experimental set-up is described whose advantage is to permit a better contact between mould and glass during the shaping process. The integration procedure of the slumped segments into the elemental module is also reviewed.

One of the most difficult requests to be accomplished from the technological point of view for next generation x-ray telescopes is to combine high angular resolution and effective area. A significant increase of effective area can be reached with high precision but at the same time thin (2-3 mm thickness for mirror diameters of 30-110 cm) glass mirror shells. In the last few years the Brera Observatory has lead a development program for realizing this kind of monolithic thin glass shell. The fused silica has been chosen as shell substrate due to its thermal and mechanical properties. To bring the mirror shells to the needed accuracy, we have adopted a deterministic direct polishing method (already used for past missions as Einstein, Rosat, Chandra) to ten time thinner shells. The technological challenge has been solved using a temporary stiffening structure that allows the handling and the machining of so thin glass shells. The results obtained with a prototype shell at an intermediate stage of its development (17’’ HEW measured in full illumination mode with x-ray) indicate that the working concept is feasible and can be further exploited using the very large Ion Beam Facility available in our labs for the final high accuracy figuring of the thin shells. In this paper we present the required tolerances for the shell realization, the shells production chain flow and the ion beam facility up grading. Forecast on figuring time and expected performances of the figuring will also be given on the basis on the metrological data collected during past shell development.

Effect of the polishing plane vibration on large-size optical workpieces in continuous polishing is studied. The vibration equation was deduced based on the existence of inclination between the polishing plane and z-axis direction. Influences of different parameters, such as the inclination, rotation speeds of the polishing plane and workpiece, the eccentricity and workpiece radius, on the polishing plane vibration were simulated. The simulations results show that rotation speeds of the polishing plane and workpiece is the most significant factor. The chaotic vibration of the polishing plane increases with increasing rotation speeds differences between the polishing plane and workpiece. When differences are small, periodic ups and downs of the polishing plane occur with the increase of polishing time. Experiments verified the influence of rotation speeds differences on the polishing plane vibration. The vibration affects PV of large-size optical workpieces in continuous polishing.

Here we show our ability to fabricate two-dimensional (2D) gratings on chalcogenide glasses with peak-to-valley amplitude of ~200 nm. The fabrication method relies on the thermal nano-imprinting of the glass substrate or film in direct contact with a patterned stamp. Stamping experiments are carried out using a bench-top precision glass-molding machine, both on As₂Se₃ optically-polished bulk samples and thermally-evaporated thin films. The stamps consist of silicon wafers patterned with sub-micron lithographically defined features. We demonstrate that the fabrication method described here enables precise control of the glass’ viscosity, mitigates risks associated with internal structural damages such as dewetting, or parasitic crystallization. The stamping fidelity as a function of the Time-Force-Temperature regime is discussed, and further developments and potential applications are presented.

Five chalcogenide glasses in the GeAsSe ternary glass system were melted, fabricated into flats, and molded between planar, uncoated, binderless WC molds using a laboratory-scale precision glass molding machine. The five glasses originate at the binary arsenic triselenide (As₄₀Se₆₀) and are modified by replacing As with Se in 5 mol% increments, or by locking the As:Se ratio and adding Ge, also in 5 mol% increments. The glasses are separated into two groups, one for the Ge-free compositions and the other for the Ge-containing compositions. This effort analyzes the differences between the Ge-containing and the Ge-free glasses on the post-molded glass and mold surface behavior, as well as the mold lifetime. Fabrication features, such as scratch and/or dig marks were present on the glass and mold surfaces prior to the PGM process. White light interferometry analysis of the surfaces shows an overall reduction in the RMS roughness of the glass after molding, and an increase of the roughness of the molds, after 15 molding cycles. After molding, the quantity of observable defects, primarily deposits and dig marks are increased for both the glass and mold surfaces. Deposits found on the WC molds and glasses were analyzed using Electron Dispersive X-ray Spectroscopy (EDS) and showed no evidence of being due to material transfer between the WC molds and the glass constituents. In general the main observable difference in the analysis of the two post molded sets, despite the changes in chemistry, is the quantity of molding induced defects near the edge of the GeAsSe samples.

For the fabrication of highly precise glass optics, Precision Glass Molding (PGM) is the state-of-the-art replicative manufacturing process. However, the process efficiency is mainly determined by the service lifetime of the molding tools and, in particular, the performance of the protective coatings. Testing the lifetime in real molding machines is extremely cost and effort intensive. In a new testing facility the protective coating performance can be evaluated by systematically inducing tool wear under realistic process conditions. A high number of pressing cycles can be executed under minimal time and material effort, reducing the cost consumption for such coating validation tests significantly. In this paper, a fast method for evaluating the performance of coatings is provided. The machine concept and evaluation method are presented in comparison to the production conditions. Investigations are targeted on the similarities between tool wear in production and those induced in the testing facility. After inducing wear patterns on test specimens in the new facility, surface alterations are characterized with light microscopy. The results show similar degradation patterns as known from production, on the coated tools. The results presented show that the facility provides unique opportunity for optimizing coatings, but also glass compositions, for use in Precision Glass Molding.

Melt spinning is a rapid quenching process that makes it possible to create materials with a very fine microstructure. Due to this very fine microstructure the melt spinning process is an enabler for diamond turning optics and moulds without the need of post-polishing. Using diamond turning of melt spun aluminium one can achieve ≤2 nm Rq surface roughness. Application areas are imaging and projection optics, mirrors, moulds for contact lenses and spectacles. One of the alloys that RSP produces is RSA-905. This alloy has a solid track record as a better and cheaper concept in the application of moulds for optical components such as contact lenses. The RSA-905 is a dispersion hardened amorphous-like alloy that keeps its properties when exposed to elevated temperatures (up to 380°C). This gives the material unique features for optics moulding applications. RSA-905 moulds are cheaper and better than traditional mould concepts such as copper or brass with or without NiP plating. In addition logistics can be simplified significantly: from typical weeks-months into days-week. Lifetime is typically in the range of 100.000 – 200.000 shots. For high volume production typically ranging from several 100.000 – several 1.000.000 shots, NiP plated steel moulds are typically used. By using an appropriate optical coating concept RSA-905 can be upgraded to a competitive alternative to steel in terms of price, performance and logistics. This paper presents some recent developments for improved mould performance of such concept. Hardness, wear resistance and adhesion are topics of interest and they can be applied by special coatings such as diamond-like carbon (DLC) and chromium nitride (CrN). These coatings make the aluminium alloy suitable for moulding mass production of small as well as larger optics, such as spectacle lenses.

We present a method developed by INAF (Italian National Institute for Astrophysics) for the manufacturing of mirrors by using commercial of-the-shelf materials. It is based on the shaping of thin glass foils by means of forced bending; then a sandwich structure is assembled for retaining the imposed shape. These mirrors are intended for optical systems with few arcmin in angular resolution working in extreme environments, being their principal mechanical features the very low weight and high rigidity. The cost and production time also turns to be very competitive. In this paper we report the main achievements of the R&D performed. We recall the investigation of the theoretical limits with finite element analyses and the process implementation. Finally, the case of the mirrors for IACT (Imaging Atmospheric Cherenkov Telescope) is presented with respect to the ASTRI project (Astrofisica con Specchi a Tecnologia Replicante Italiana).

Precision glass molding (PGM) is an optical manufacturing process used to hot press optical glass into a specified lens shape. This is done by taking the glass to a temperature above T_g and exerting force using an upper and lower mold. These molds will, together, give the pressed lens its shape. This study focuses on the high temperature interactions between the mold tooling material and two optical oxide glasses, Ohara’s L-BAL35 and Schott’s N-FK5. Flat molds were used to press flat glass work pieces at high temperature and force; key post process parameters such as sample and mold surface contamination using EDS and visible degradation via SEM were catalogued and analyzed. The molds used were bare tungsten carbide (WC) and silicon carbide (SiC) with an amorphous SiC chemical vapor deposition (CVD) coating. The results showed that raw WC molds suffered the most degradation including physical damage as well as chemical adherence and reaction. The Ti binder used in the WC as well as some the tungsten itself transferred to both glasses and caused a white reflective layer to appear on the molded glass surface. Severe damage was evident after only 2 pressing cycles with potassium from N-FK5 being the most prominent chemical contaminant. N-FK5 proved to be the more corrosive of the two glasses in all occasions. The SiC coated molds fared better in terms of degradation than the WC, however sticking of glass to mold was a problem.

The properties of Kummer beams propagation and transformation in optical metamaterials are studied. The possibility is established and conditions are determined for unidirectional and opposite directional propagation of Kummer light beams phase and the longitudinal component of its energy flux in metamaterials. The reflection and refraction coefficients of arbitrary Kummer beam are represented as superposition of linear combinations of reflection and refraction ones of TM- and TE- polarized Kummer beams. These properties are studied in the LG (Laguerre-Gaussian) beams and in Bessel beams. The main goal is to compare these three beams and to show the Kummer´s advantage. To use these mathematical functions a Computer Algebra Software has been used, specifically Maple.

Due to their economical and easy-manageable advantages, POFs (polymer optical fiber) are going to replace traditional communication media such as copper and glass step by step within short distance communication systems. POFs are already used in various fields of optical communication, e.g. the automotive sector or in-house communication. Though single channel communication systems are state of the art technology, using of only one channel/wavelength for communication limits the bandwidth. For future scenarios this traditional technology is the bottleneck of bandwidth, particularly for HDTV with IP-TV. One solution to breakthrough this limitation is to use more than one wavelength over one single fiber, this is called WDM (wavelength division multiplexing) and is well-established for GOF communication. This technique will be adapted for the visible spectrum for POF. However this multiplexing technology requires two more key-elements: a multiplexer, which combines the multiple wavelengths signals into one fiber, and a demultiplexer at the end of the network to separate the colored signals. In this paper, the development of this key-element based on a Rowland spectrometer will be shown. It starts with the simulation, this is done by means of raytracing. Also the next process steps and solutions for injection molding are described.

The preliminary results in the fabrication of off-axis optical surfaces are presented. The propose using the conventional polishing method and with the surface under mechanical stress at its edges. It starts fabricating a spherical surface using ZERODUR® optical glass with the conventional polishing method, the surface is deformed by applying tension and/or compression at the surface edges using a specially designed mechanical mount. To know the necessary deformation, the interferogram of the deformed surface is analyzed in real time with a ZYGO® Mark II Fizeau type interferometer, the mechanical stress is applied until obtain the inverse interferogram associated to the off-axis surface that we need to fabricate. Polishing process is carried out again until obtain a spherical surface, then mechanical stress in the edges are removed and compares the actual interferogram with the theoretical associated to the off-axis surface. To analyze the resulting interferograms of the surface we used the phase shifting analysis method by using a piezoelectric phase-shifter and Durango® interferometry software from Diffraction International™.

In this paper, we propose a Quasi Common-Path Interferometer based on a two beams configuration using simultaneous phase shifting interferometry modulated by polarization. Due to the fact that the configuration is capable of obtaining two beams whose separation can be varied, according to the characteristics of the grid used, to obtain the interference patterns. It can be used to implement a quasi-common path interferometer that allows the measurement of dynamic events with high accuracy. For demodulate the fringe patterns generated by the optical system we using the conventional four step phase shifting method. Experimental results are also given.

The French Laser MégaJoule (LMJ) will include 176 square beams involving hundreds of large optical components. Wavefront performances of all these components are critical to achieve the desired focal spot shape and to limit hot spots that could damage the components. These specifications are usually checked with interferometric setups. This can be uneasy to achieve for specific components such as multi-dielectric mirrors or gratings because one has to use the exact nominal configuration (wavelength, incidence, geometry of the incident beam) to perform the measurement. For the smallest spatial periods, classical techniques like interferometric microscopes fail to measure the wavefront and propose a "surface" measurement that can lead to misinterpretations. We present in this paper measurement methods based on a laser beam diffraction interpretation that can efficiently replace the usual techniques. The first technique consists in measuring intensity level of the dim scattered "corona" around the focal spot. The second one is based upon image processing of near-field acquisitions by the means of Fourier analysis and the Talbot effect theory. Those techniques do not lead to a phase map as classical techniques do but they give access to the Power Spectral Density of wavefront defects over a large spatial frequency bandwidth. For many applications, this is enough information to estimate the component performance. We present results obtained by this way on LMJ components and a comparison with Fizeau interferometer measurement.

The absolute testing method can be used to test the freeform lens. There are some spatial frequencies terms can’t be getting by the traditional absolute testing method such as even and odd functions method, rotation shear method, rotated equally spaced position method. In this paper we will show the losing terms in the traditional method. In this paper the freeform surface is created by 300th Zernike polynomials. The freeform lens is based on the flat lens. We use the Zernike polynomial to simulate the two flats and use the freeform surface as the three flat. According to the three flat absolute testing methods, we can simulate the testing result. The freeform flat which we use is polishing by the ion figuring machine of NTG.

Infra-Red (IR) objective achieves a few micrometers of spatial resolution with high Numerical Aperture (NA) of about 0.75, for example, in mid-IR. However, submicron resolution is hard to achieve in Mid-IR because of the long wavelength compared to the visible range. To overcome the limitation, a solid immersion lens (SIL) is incorporated into the conventional objective so that the high refractive index of SIL contributes to obtain the high spatial resolution image of sample immersed in SIL. Germanium is a typical material of SIL in the infrared wavelengths because of the high refractive index and the high transmittance. In our study, we fabricated a Germanium-SIL using the quantified parameters of the ultra precision machining. The parameters are tool rake angle, cutting speed, feed rate, and depth of cut. The surface shape of the fabricated SIL was measured with the accuracy of 0.0376 μm in RMS and 0.3159 μm in P-V. We applied the fabricated SIL to a custom IR objective to investigate the improvement of its spatial resolution. Optical performance of the IR objective was evaluated with and without SIL. As results, the IR objective with SIL achieved 1.23 μm of the spatial resolution from the 3.9 μm of IR objective without SIL

Freeform and conformal optics represent the next generation of optical systems where their utilization leads to more compact, lighter, and higher performance systems for solar collectors, consumer optics, and defense applications. Optical coordinate measuring machines present one option for accurate metrology of freeform components but have two limitations: metrology system errors and optical probe errors. In this work, we address the latter of the two by demonstrating a compact optical probe capable of fiber delivery and fiber detection to remove potential heats sources away from measured optic. A bench top demonstrator has yielded a displacement resolution below ±10 nm and has a noise floor of approximately ±18 μrad for surface slope in two orthogonal directions. In this Proceedings, we discuss our probe concept, operating principle, and preliminary measurements with a bench top proof-of-concept system. The goal of this work is to ultimately integrate this probe into OptiPro’s UltraSurf, a 5-axis optical coordinate measuring machine for measuring freeform and conformal optics.

For the assembly of any kind of optical systems the precise centration of every single element is of particular importance. Classically the precise alignment of optical components is based on the precise centering of all components to an external axis (usually a high-precision rotary spindle axis). Main drawback of this timeconsuming process is that it is significantly sensitive to misalignments of the reference (e.g. the housing) axis. In order to facilitate process in this contribution we present a novel alignment strategy for the TRIOPTICS OptiCentric® instrument family that directly aligns two elements with respect to each other by measuring the first element’s axis and using this axis as alignment reference without the detour of considering an external reference. According to the optical design any axis in the system can be chosen as target axis. In case of the alignment to a barrel this axis is measured by using a distance sensor (e.g., the classically used dial indicator). Instead of fine alignment the obtained data is used for the calculation of its orientation within the setup. Alternatively, the axis of an optical element (single lens or group of lenses) whose orientation is measured with the standard OptiCentric MultiLens concept can be used as a reference. In the instrument’s software the decentering of the adjusting element to the calculated axis is displayed in realtime and indicated by a target mark that can be used for the manual alignment. In addition, the obtained information can also be applied for active and fully automated alignment of lens assemblies with the help of motorized actuators.

High precision optics depend on precisely aligned lenses. The shift and tilt of individual lenses as well as the air gap between elements require accuracies in the single micron regime. These accuracies are hard to meet with traditional assembly methods. Instead, lathe centering can be used to machine the mount with respect to the optical axis. Using a diamond turning process, all relevant errors of single mounted lenses can be corrected in one post-machining step. Building on the OptiCentric® and OptiSurf® measurement systems, Trioptics has developed their first lathe centering machines. The machine and specific design elements of the setup will be shown. For example, the machine can be used to turn optics for i-line steppers with highest precision.

The adjustment of opto-mechanical components in manufacturing processes often requires precise motion in all six degrees of freedom with nanometer range resolution and absence of hysteresis. Parallel kinematic systems are predestined for such tasks due to their compact design, low inertia and high stiffness resulting in rapid settling behavior. To achieve adequate system performance, specialized motion controllers are required to handle the complex kinematic models for the different types of Hexapods and the associated extensive calculations of inverse kinematics. These controllers often rely on proprietary command languages, a fact that demands a high level of familiarization. This paper describes how the integration of fieldbus interfaces into Hexapod controllers simplifies the communication while providing higher flexibility. By using standardized communication protocols with cycle times down to 12.5 μs it is straightforward to control multiple Hexapods and other devices by superordinate PLCs of different manufacturers. The paper also illustrates how to simplify adjustment and alignment processes by combining scanning algorithms with user defined coordinate systems.

Gallium Phosphide (GaP) is widely used semiconductor material, but can be also used as a material for visible and infrared optical elements. Combination of its optical and mechanical properties such as high mechanical durability, transparency from visible to infrared wavelengths and high refractive index makes it very interesting material for design of high performance optical systems in NIR and MWIR. Manufacturing of optical elements for such wavelength ranges is shifting from traditional grinding and polishing techniques to a more versatile SPDT machining. It is therefore useful to employ SPDT in production of optical surfaces on GaP. As the GaP is similar to GaAs, but harder and more brittle, all all the problems already known for GaAs are present. Here we report results of experiments with SPDT machining of optical surfaces on GaP substrates and comparison with classical machining methods.

Careful characterization of the removal function of sub-aperture polishing tools is critical for optimum polishing results. Magnetorheological finishing (MRF®) creates a polishing tool, or “spot”, that is unique both for its locally high removal rate and high slope content. For a variety of reasons, which will be discussed, longer duration spots are beneficial to improving MRF performance, but longer spots yield higher slopes rendering them difficult to measure with adequate fidelity. QED’s Interferometer for Stitching (QIS™) was designed to measure the high slope content inherent to non-null sub-aperture stitching interferometry of aspheres. Based on this unique capability the QIS was recently used to measure various MRF spots in an attempt to see if there was a corresponding improvement in MRF performance as a result of improved knowledge of these longer duration spots. The results of these tests will be presented and compared with those of a standard general purpose interferometer.