This PDF file contains the front matter associated with SPIE Proceedings Volume 8838, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Light scattering metrology has become more and more important with the development of cutting-edge optical components and systems. Light scattering is also a very versatile tool for the characterization of nanostructures and defects. While optical engineering and manufacturing are striving for ever increasing resolution of optical devices and lowest optical losses, the demands for highly resolved light scattering metrology have become extremely challenging. In this sense, “highly resolved” means: (i) measurements with high angular resolution, not just in one plane but within the entire scattering sphere, (ii) small near-angle limits, (iii) highest sensitivities and lowest instrument signatures close to or even below the Rayleigh scattering limit, as well as (iv) at-wavelength operation and, more recently, spectral resolution. Instruments for scatter measurements developed at Fraunhofer IOF to meet these demands are presented together with practical examples of application comprising roughness, sub-surface damage, and defects of polished surfaces and thin film coatings. Compact tools like a table-top 3D scatterometer and a CMOS-based scatter sensor are presented. Finally, we report on the development of a new instrument for spectroscopic angle resolved scatter measurements based on an OPO tunable laser.

In the mid-1970’s it became apparent that incident plane scatter data could be represented by simple two or three parameter expressions. This realization made possible the generation of stray light estimation codes which are used on everything from military weapons, to telescopes, to car headlights to flat panel display systems. Almost all of these applications estimate hemispherical scatter from incident plane measurements. The authors’ 2012 review of this process was limited to samples scattering just from surface roughness. In this paper hemispherical measurements are compared to calculations made from incident plane measurements using isotropic samples that scatter from bulk irregularities as well as surface scatter. The issue of non-isotropic samples is briefly introduced. The data is also analyzed to investigate reciprocity.

The Rayleigh Rice vector perturbation theory has been successfully used for several decades to relate the surface power spectrum of optically smooth reflectors to the angular resolved scatter resulting from light sources of known wavelength, incident angle and polarization. A similar relationship should be available for the situation of a beam transmitting from a region of index greater than 1.0 into a region of unit index through an optically smooth surface. This paper presents such a relationship and compares the result to measured scatter data at two light wavelengths.

The Rayleigh Rice vector perturbation theory has been successfully used for several decades to relate the surface power spectrum of optically smooth reflectors to the angular resolved scatter resulting from light sources of known wavelength, incident angle and polarization. While measuring low frequency roughness is relatively easy, the corresponding near specular scatter can be difficult to measure. This paper discusses using high incident angle near specular measurements along with profile generated surface power spectrums as a means of checking a near specular scatter requirement. The specification in question, a BRDF of 1.0 sr^-1 at 2 mrad from the specular direction and at a wavelength of 1μm, is very difficult to verify by conventional scatter measurements. In fact, it is impractical to directly measure surface scatter from uncoated Zerodur because of its high bulk scatter. This paper presents profilometer and scatterometer data obtained from coated and uncoated flats at several wavelengths and outlines the analysis technique used to check this tight specification.

It is considered challenging to evaluate the sparse microdefects of large optical surfaces because the microdefects are usually of microns while the test samples are of hundreds of millimeters. Most of the existing methods encounter problems such as uncertainty and inefficiency in eyeballing, inconsequence between laser source and international standard, limitation of detecting area, qualitative but not quantitative nor standard measurement of defects, etc. In this paper, a dark-field microscopic scattering imaging system for microdefects evaluation is introduced. The principle of the proposed surface microdefect evaluation system will be presented and the experiment results on evaluating numerous of test samples will be given.

The software configurable optical test system (SCOTS) is an efficient metrology technology based on reflection deflectometry that uses only an LCD screen and a camera to measure surface slope. The surface slope is determined by triangulations using the coordinates of the display screen, camera and test mirror. We present our recent SCOTS test results concentrated on high dynamic range measurements of low order aberrations. The varying astigmatism in the 91 cm diameter aspheric deformable secondary mirror for the Large Binocular Telescope (LBT) was measured with SCOTS, requiring no null corrector. The SCOTS system was designed on axis with camera and screen aligned on the optical axis of the test mirror with the help of a 6 inch pellicle beam splitter. The on-axis design gives better control of the astigmatism in the test. The high dynamic range of slope provided a measurement of astigmatism with 0.2 μm rms accuracy in the presence of 231 μm peak-to-valley (PV) aspheric departure. The simplicity of the test allowed the measurements to be performed at multiple elevation angles.

We describe a systematic procedure developed for surface characterization of super polished x-ray optical components with an interferometric microscope. In this case, obtaining trustworthy metrology data requires thorough accounting of the instrument’s optical aberrations, its spatial resolution, and random noise. We analyze and cross compare two general experimental approaches to eliminate the aberration contribution. The reference surface approach relies on aberration evaluation with successive measurements of a high quality reference mirror. The so called super smooth measurement mode consists of subtracting two surface profiles measured over two statistically uncorrelated areas of the optics under test. The precisely measured instrument’s modulation transfer function (MTF) and random noise spectrum allows us to correct the aberration-amended surface topography in the spatial frequency domain. While the developed measurement procedure is general and can be applied to various metrology instruments, the specific results presented are from a Zygo NewView™ 7300 microscope.

The measurement of large departure aspheres and windows is a challenge for the optics community. OptiPro systems has developed a non-contact measuring system called UltraSurf to overcome these difficulties. The UltraSurf system utilizes a single point non-contact sensor coupled with high accuracy air bearings to scan optical surfaces. Five air bearing axes allow for the optical probe to maintain normal angles with the surface under test, and provide a smooth and accurate scan. The axes of motion allow scanning of rotationally symmetric parts such as spheres and aspheres, but also give it the freedom to perform areal surface scanning and freeform metrology. By maintaining a tangent angle with the surface, this technique allows for large surface slopes and deviation from best fit sphere to easily be measured. Several commercial non-contact sensors have been integrated into UltraSurf. The sensors operate with different optical principles, allowing for greater flexibility of the types of surfaces to be measured. One sensor applies white-light confocal chromatic aberration for high resolution, single surface measurement. Another sensor that uses low-coherence interferometry with a 1310 nanometer light source is able to see through materials, enabling multiple surface and thickness measurements simultaneously. Measurement of large departure aspheres and windows will be demonstrated. Cross comparison of UltraSurf data with current metrology techniques will be shown on surfaces that can be measured with multiple methods.

Together with the group of interferometry based systems, coordinate measurement machines are an essential part of the metrology in the modern optical industry. Coordinate measurement machines commonly consist of a multi axes framework. They are designed to operate in a defined three dimensional work zone, where every possible point can be reached by the measurement tool tip. This basic design principle leads to some interdependent challenges. A detailed measurement result needs a large amount of measurement points to detect even minor irregularities and short-wave errors. However, a rising of the amount of measurement points increases the corresponding measurement time analogous. On the other hand, the extended operation time increases the access of undesired thermal and dynamic influences, which cause multiple errors to the measurement result. Furthermore, modern production processes need rapid metrology systems to aid the machining time. This paper discusses results obtained by operating with three different measurements in order to find an agreement between speed and certainty of the coordinate measurement machine. The topographic coordinate measurement system TII- 3D had been re-developed at the University of Applied Sciences Deggendorf in the laboratory of optical Engineering and it is equipped with three different measurement strategies. The first mode, the Track-Mode operates in concentric circles on top of the surface of the object to be measured. The Spiral-Mode measures along a dynamic moveable spiral line and the Section-Mode produces multiple cross-sections.

Increasing demand for highly accurate freeform aspheric surfaces requires accurate and efficient measurement techniques. One promising possibility uses a sub-aperture scanning system that measures local curvature variations across the part. In this paper, we develop and demonstrate two different data processing algorithms, a zonal approach using Southwell integration method and a modal approach leveraging Zernike curvature basis, that reconstruct the surface 3-dimensional profiles from the curvature data. The performance of suggested methods and the sensitivity to noise is diagnosed for various SNR (Signal-to-Noise Ratio) cases.

Sub-aperture testing methods are widely used in optical shops to test surface deformations of large diameter, high numerical aperture, or aspherical lens surfaces. We are proposing a novel 4 axis vibration modulated interferometer for subaperture testing. This interferometer takes advantage of the rotationally symmetric property of the optical lens and measures the lens surface against its symmetry axis rotationally. By adapting a synchronous random phase modulation measurement, interferometric data is acquired on the fly when the lens is being rotated. The vibration modulated interference phase is then calculated and stitched into a complete lens surface map by least squared fitting. This method has advantages over the prior methods in that it acquires the interferogram in a much shorter acquisition time, even with lower requirements on the optics and mechanical hardware. The stitch error is then significantly decreased by increasing both the lateral resolution of sub-aperture and the reduced position uncertainty of the stitched sub-aperture phase maps. A measurement on a mild asphere is demonstrated to prove the feasibility of the proposed interferometer.

Subaperture stitching extends measurements such as interferometry by combining several overlapping measurements into a single, high-accuracy estimate of the overall image. In designing a subaperture measurement regimen, there are several tradeoffs related to size, quantity and locations of subapertures within the full aperture of the test optic. Understanding how individual subaperture measurement noise couples through these parameters into errors in the final stitched map is important for estimating overall system performance. In this work, we explore parametric rules for estimating the accuracy of stitched results based on subaperture geometry parameters and noise characteristics for a self-calibrating system where both a test optic and reference optic are simultaneously determined. From these rules, we examine types of errors introduced by stitching which enables confidence estimates for the final stitched map surface quality.

In the field of precision optics the interferometry is the most applied measurement method to test spherical and flat objects. In principle, a standard interferometer setup is limited to these surface geometries, but interferometric systems may be modified with the aid of CGH’s or the stitching technology. As a consequence aspherical shapes and even freeform optics are measurable up to a certain extent. In an interferometric measurement the measured variable is the optical path difference (OPD) between the reference wave and the test wave. Based on the detected OPD the surface error of the test object is calculated by phase shifting methods for instance. It is evident, that the error from the reference surface affects the determination of the test object surface error. One option to face this problem is the calibration of the system prior to the measurement. For this the determination of the reference surface error may be realized with the aid of a two sphere test or a random ball test e.g. [1]. In the well-known SSI-technology from QED technologies the reference surface error is calculated on the basis of the sub-measurements. Due to the self-calibrating nature of the QED stitching principle [2-4] a calibration of the system prior to the measurement is not necessary. The University of Applied Sciences Deggendorf has implemented a similar algorithm to estimate the reference wave front error, or to be exact the error of the whole optical system, based on a multiple set of sub-measurements. This paper describes the applied algorithm in detail and discusses the results. To verify the implemented tool the results are compared to the outcomes of the QED stitching software.

Refinements in computer controlled optical surfacing allow efficient grinding and polishing of meterclass optics to accuracy limited only by the surface metrology. We present a categorization of metrology methods and their implementation for meter-class optical components. Interferometry with computer generated holograms provides nanometer accuracy for full surface measurements of a wide range of convex and concave aspheric surfaces. For measuring off-axis and freeform aspheric surfaces, the holograms include features that provide references for alignment. Very high spatial resolution is achieved with subaperture interferometric measurements which can be stitched together to provide a full-aperture map. Scanning systems complement the capabilities of interferometry by achieving larger dynamic range and providing independent corroboration. Optical coordinate measurement machines (CMMs) provide non-contact measurements of surfaces in their ground state to guide figuring, as well as highly accurate measurements of finished optics. Scanning systems for measuring flat mirrors provide excellent resolution and absolute accuracy. The performance and practical issues for this full array of measurement techniques are presented to show the relative strengths of each method.

The High Efficiency and Resolution Multi Element Spectrograph (HERMES) for the Australian Astronomical Observatory (AAO) uses four large aperture, high angle of incidence volume phase holographic gratings (VPHG) for high resolution ‘Galactic archaeology’ spectroscopy. The large clear aperture, the high diffraction efficiency, the line frequency homogeneity, and mosaic alignment made manufacturing and testing challenging. We developed new metrology systems at the AAO to verify the performance of these VPH gratings. The measured diffraction efficiencies and line frequency of the VPH gratings received so far meet the vendor’s provided data. The wavefront quality for the Blue VPH grating is good but the Green and Red VPH gratings need to be post polishing.

Interferometry with computer generated holograms (CGHs) has become the industry standard for accurate measurements of aspheric optical surfaces. The CGH is a diffractive optical element that can be designed to create virtually any phase or amplitude distribution, and can be accurately manufactured using methods and equipment developed for integrated circuit production. Surface measurements with nanometer level precision can be performed using accurately wellcalibrated equipment. This paper provides a systematic analysis of all significant sources of error for CGH metrology, including encoding error, pattern distortion, substrate irregularity and calibration, and system alignment.

We evaluate a method for testing the radius of a spherical surface with a hologram that consists of a pair of nested Fresnel zone lenses. The hologram is positioned in the collimated test beam of a Fizeau interferometer. The inner zone lens generates a focus at the test part surface, whereas the wavefront of the first diffraction order of the outer zone lens is confocal with the test part. When the test part radius is equal to the nominal radius, the fringes in both zone lens areas are nulled at the same distance of the test sphere from the zone lens. The radius error of the spherical surface can be calculated from the test sphere displacement between interferometer null positions for the inner and outer zone lenses, or from the defocus term of the outer (confocal) lens at the position of zero defocus of the inner (cat’s-eye) zone lens. The primary benefits of the nested zone lens method are its ease of use, and that it enables radius measurements of spherical surfaces with large radii. We describe the radius measurement of a precise convex sphere with a nominal radius of 80mm.

In experiments of inertial confinement fusion (ICF), the thickness uniformity of capsule and the density uniformity of deuterium-tritium (DT) ice are both key to successful ignition, while the cross-grating lateral shearing interferometer (CGLSI), which is accurate and insensitive to disturbance, can be employed to test the density distribution of DT ice precisely. In this paper, a wavefront retrieval method for CGLSI based on differential Zernike polynomial fitting is presented. Fast Fourier Transform technique (FFT) is employed to get the frequency spectrum of the interferogram obtained by CGLSI. By performing Inverse Fast Fourier Transform (IFFT) of the +1 order spectrum in both X and Y directions, it is possible to extract shearing wavefronts from the interferogram in both two orthogonal directions. Utilizing differential Zernike polynomial fitting method, we are capable of integrating two shearing wavefronts in both X and Y directions together and retrieving the wavefront under testing. In the process of solving Zernike coefficients, the characteristics of differential Zernike orthogonal polynomials should be taken fully into account in mathematical modeling. To avoid the retrieval error introduced due to matrix mutation, the determination of discrete grid number and aperture shape must be in line with the theory that Zernike polynomials are orthogonal over a unit circle as well. The result of simulation analysis shows that the wavefront retrieval method for CGLSI based on differential Zernike polynomial fitting is correct and accurate, and the root-mean-square error of this method is less than λ/15.

We report on the first-ever demonstration of grinding and polishing full-size, off-axis aspheric, mirror segments as prototypes for an extremely large telescope, processed entirely in the final hexagonal shape. We first describe the overall strategy for controlling form and mid spatial frequencies, at levels in the vicinity of <10nm RMS surface. This relies first on direct CNC grinding of the base-form of these 1.4m segments, using the Cranfield BoX™ machine. The segments are then mounted on a custom designed (Optic Glyndwr Optoelectronic Engineering Group) three segment hydraulic support, and CNC polished on a Zeeko IRP 1600 machine using a variety of custom tooling. We overview the fullaperture and sub-aperture metrology techniques used to close the process-loop and certify quality, all of which operate with the segment in-situ on the IRP1600. We then focus on the pristine edge-definition achieved by the combination of tool-lift and smoothing operations; results never previously demonstrated on full-size pre-cut hexagonal segments. Finally, the paper discusses the feasibility of scaling the process to deliver 931 segments in seven years, as required for the E-ELT project.

The Decadal Survey stated that an advanced large-aperture ultraviolet, optical, near-infrared (UVOIR) telescope is required to enable the next generation of compelling astrophysics and exoplanet science; and, that present technology is not mature enough to affordably build and launch any potential UVOIR mission concept. Under Science and Technology funding, NASA’s Marshall Space Flight Center (MSFC) and Exelis have developed a more cost effective process to make up to 4m monolithic spaceflight UV quality, low areal density, thermally and dynamically stable primary mirrors. A proof of concept mirror was completed at Exelis and tested down to 250K at MSFC which would allow imaging out to 2.5 microns. The parameters and test results of this concept mirror will be shown. The scale-up process will be discussed and the technology development path to a 4m mirror system by 2018 will also be outlined.

Aspheric optics can pose as a challenge to the manufacturing community due to the surface shape and level of quality required. The aspheric surface may have inflection points that limit the usable tool size during manufacturing, or there may be a stringent tolerance on the slope for mid-spatial frequencies that may be problematic for sub-aperture finishing techniques to achieve. As aspheres become more commonplace in the optics community, requests for more complex aspheres have risen. OptiPro Systems has been developing technologies to create a robust aspheric manufacturing process. Contour deterministic microgrinding is performed on a Pro80 or eSX platform. These platforms utilize software and the latest advancements in machine motion to accurately contour the aspheric shape. Then the optics are finished using UltraForm Finishing (UFF), which is a sub-aperture polishing process. This process has the capability to adjust the diameter and compliance of the polishing lap to allow for finishing over a wide range of shapes and conditions. Finally, the aspheric surfaces are qualified using an OptiTrace contact profilometer, or an UltraSurf non-contact 3D surface scanner. The OptiTrace uses a stylus to scan across the surface of the part, and the UltraSurf utilizes several different optical pens to scan the surface and generate a topographical map of the surface under test. This presentation will focus on the challenges for asphere manufacturing, how OptiPro has implemented its technologies to combat these challenges, and provide surface data for analysis.

Freeform surfaces provide more design freedoms to imaging system without introducing new types of aberrations, therefore better performance can be expected. In this paper, the design of a four-mirror telescope with freeform surfaces was introduced and issues such as tolerancing , manufacturability were discussed; Based on that, fabrication and testing of freeform surfaces were discussed; Particularly direct CNC generation, deterministic polishing techniques including CCOS, MRF and IBF Polishing were presented in detail. Since testing is critical to make high accurate freeform surfaces, the paper focused on Computer Generated Hologram (CGH) design and implement to measure large freeform mirrors. In particular, correction of detector to mirror mapping distortion was discussed in detail. Finally, the full field alignment results were given to show the feasibility of using large freeform surfaces in space optics.

This article describes the progress in the area of modern centration technology by using digital image processing. This work is motivated by the continuously increasing demand for high-end optics. During the last years the surface lens quality has been continuously improved. Today the image quality is more determined by the manufacturing tolerances for the mechanical interface which is responsible for decenter and tilt of the lenses respectively the subgroups. Some of the aberrations are directly linked to the decenter of the lenses, Coma for example. Hence it is necessary to realize the subgroups with tolerances below lpm. To determine the decenter of a lens an auto collimation telescope is used to image the reflex of the lens surfaces onto a detector, commonly a half covert photodiode. Rotating the lens generates a sinusoidal signal, which is evaluated by a lock-in amplifier to drive two actuators to adjust the alignment chuck. Typical internal reflections caused by stray light for example disturb the current procedure in such a way that it is impossible to get a stable alignment process. Digital image processing allows us to fix these problems with image recognition. We will demonstrate how a modified auto collimation telescope in combination with the developed software algorithms made the manufacturing process more accurate, faster and useable for a broad spectrum of lenses. It has been proofed by some thousand diverse lenses that with these new technique subgroups can be centered within 0.25μm.

On one hand, the “float polishing” process consists of a tin lap having many concentric grooves, cut from a flat by single point diamond turning. This lap is rotated above a hydrostatic bearing spindle of high rigidity, damping and rotational accuracy. The optical surface thus floats above a thin layer of abrasive particles. But whilst surface texture can be smoothed to ~0.1nm rms (as measured by atomic force microscopy), this process can only be used on flat surfaces. On the other hand, the CNC “fluid jet polishing” process consists of pumping a mixture of water and abrasive particles to a converging nozzle, thus generating a polishing spot that can be moved along a tool path with tight track spacing. But whilst tool path feed can be moderated to ultra-precisely correct form error on freeform optical surfaces, surface finish improvement is generally limited to ~1.5nm rms (with fine abrasives). This paper reports on the development of a novel finishing method, that combines the advantages of “fluid jet polishing” (i.e. freeform corrective capability) with “float polishing” (i.e. super-smooth surface finish of 0.1nm rms or less). To come up with this new “hybrid” method, computational fluid dynamic modeling of both processes in COMSOL is being used to characterize abrasion conditions and adapt the process parameters of experimental fluid jet polishing equipment, including: (1) geometrical shape of nozzle, (2) position relative to the surface, (3) control of inlet pressure. This new process is aimed at finishing of next generation X-Ray / Gamma Ray focusing optics.

This paper reports on an improvement of the surface roughness in A-FJP by utilisation of a perforated polishing pin. The University of Applied Science Deggendorf is currently working on the A-FJP process to investigate the effects on the resulting surface roughness on optical lenses.

While post-polish has previously been shown to greatly enhance the surface quality, surface roughness, and surface figure of single-point diamond turned Aluminum mirrors, the field of bare Aluminum polishing continues to advance. New results demonstrating improvement in mid-spatial frequency errors and methods for adapting to a wider range of Aluminum materials constitute the next generation of polished Aluminum mirrors. These results show new levels of surface finish, correlated with BRDF measurements. Complimentary enhancements have been made by achieving new levels of precision in the placement of the optical axis relative to datum features, enabling significant alignment time savings.

Modern advanced optical systems often require challenging high spatial frequency surface error control during their optical fabrication processes. While the large scale surface figure error can be controlled by directed material removal processes such as small tool figuring, surface finish (<<1mm scales) is controlled with the polishing process. For large aspheric optical systems, surface shape irregularities of a few millimeters in scale may cause serious performance degradation in terms of scattered light background noise and high contrast imaging capability. The conventional surface micro roughness concept in Root Mean Square (RMS) over a very high spatial frequency range (e.g. RMS of 0.5 by 0.5 mm local surface map with 500 by 500 pixels) is not sufficient to describe or specify these surface characteristics. For various experimental polishing conditions, we investigate the process control for high frequency surface errors with periods up to ~2-3mm. The Power Spectral Density of the finished optical surfaces has been measured and analyzed to relate various computer controlled optical surfacing parameters (e.g. polishing interface materials) with the high spatial frequency errors on the surface. The experiment-based optimal polishing conditions and processes producing a super smooth optical surface while controlling surface irregularity at the millimeter range are presented.

UltraForm Finishing (UFF) is a deterministic sub-aperture computer numerically controlled grinding and polishing platform designed by OptiPro Systems. UFF is used to grind and polish a variety of 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 accurately measure the dynamic coefficient of friction (μ), how it changes as a function of belt wear, and how this ultimately affects material removal rates. The coefficient of friction has been examined in terms of contact mechanics and Preston’s equation to determine accurate material removal rates. By accurately predicting changes in μ, polishing iterations can be more accurately predicted, reducing the total number of iterations required to meet specifications. We have established an experimental apparatus that can accurately measure μ by measuring triaxial forces during translating loading conditions or while manufacturing the removal spots used to calculate material removal rates. Using this system, we will demonstrate μ measurements for UFF belts during different states of their lifecycle and assess the material removal function from spot diagrams as a function of wear. Ultimately, we will use this system for qualifying belt-wheel-material combinations to develop a spot-morphing model to better predict instantaneous material removal functions.

Conventional or chemo-mechanical polishing represents the polishing technology most often applied for manufacturing precision glass optics. It is applied on various machine types and for all kinds of geometries. But it still represents the manufacturing step with the lowest process stability. This work deals with the analysis and descriptive modeling of contact conditions occurring in the process area. The polishing process is assumed as a hydrodynamic system. The model aims for a qualitative description of the formation of a fluid film between pad and surface. The models enable the theoretical discussion of the effects of major process parameters on the fluid film thickness. Secondly, the theoretical considerations are validated by experiments on a tribometer. With this test bench the effects of the polishing parameters as well pad properties on the contact conditions are investigated. Additional experiments are conducted on a polishing machine for validation the results. It is found, that the hydrodynamic theory describes the formation of fluid film in polishing. Under typical polishing conditions, the friction regime is in the range of mixed friction. That means pad asperities and polishing grains are not completely separated from the surface by a fluid film. The transition into erosive wear and pure liquid friction was not reached. But an analysis of the surface quality in dependence on the relative speed showed, that the quality starts decreasing after a minimum, far before reaching the transition point. Based on the derived qualitative description, the effects of process parameters and pad properties on the fluid film can be discussed.

Four-axis single point diamond machining is a diamond machining technique recently introduced as a higher speed alternative to 3-axis micro-milling for the fabrication of arrays of spherical miniature lenses. For some applications of lens arrays, aspheric lenses are preferred over spherical lenses. In this study, an array of aspheric lens surfaces that were designed for an array microscope for digital pathology were fabricated, and the surface quality was found to have the same surface accuracy as previous experiments with 4-axis SPDM with an “open loop” tool path correction process. The open loop process demonstrated here will lead to additional time savings when fabricating an array microscope compared to the more common closed loop compensation processes. This study also shows that the 4-axis SPDM is capable of producing arbitrary surfaces with high surface quality, enabling technologies such as array microscopy.

There are over one hundred types of glass that are sold as moldable grades. These moldable glasses are manufactured by a limited number of suppliers; each manufacturer with their own grade and designation. Many of these grades can be found to have groupings across the manufacturers, indicating possible equivalency. Equivalency of materials is an important consideration for an optical system as it would eliminate dependency on a single source, and generate cost competition. In order to establish optical equivalency it is necessary to establish significant similarity between materials. This paper compares moldable glass grades from several equivalent glass types from different manufacturers both theoretically and experimentally. Experimental data is based on precision glass molding of the same lens using different but equivalent grades of glass and using standard lens criteria for comparison. Conclusions on whether specific glass types are truly equivalent are then established.

In this research, ultra-precision slow tool servo (STS) diamond turning technique has been adopted to generate a freeform surface. In the previous studied, we have developed a model of three-dimensional (3-D) tool shape compensation for generating 3-D tool path in STS diamond turning of asymmetrically freeform surface. However, the form error is not acceptable when the surface sagitta or tangential slope variation too large. Therefore, the surface form error compensation method has been developed in this studied. The surface form error has been compensated from 3μm to less than 1μm by the compensation method.

Lens molding has become the promising technique to conduct mass produce of aspheric glass lens. It overcomes some disadvantages of traditional grinding or turning methods, such as high cost, low efficiency, unstable accuracy, and so on. Up to now, the lens molding process has been looked on as one of the reliable methods in fabrication of aspheric glass lens. However, in real production, one has found that it’s hard to control the molding parameters, e.g. molding temperature, molding period, molding speed and pressing pressure, etc. Therefore it’s necessary to develop the specific molding processes for a certain glass material. In this paper, SCHOTT P-SK57 is adopted to carry out the lens molding analysis in order to achieve the relative processing parameters. The molding cases are analyzed based on three different temperatures of 510°C, 520°C, and 530°C, higher than transition point 493°C of P-SK57. Through continuous heating and pressing simulation, the results show that the best pressing temperature could be about 530°C, at which the residual stress is only 5.22MPa (with the molding speed of 0.1mm/s).

We have been working in a method for testing fast aspheric convex surfaces with flat null screens in an array of LCD’s, based on the null screen principles accordingly; i.e. we have demonstrated qualitatively that using three LCD’s forming a triangular prism, we can evaluate aspheric fast surfaces instead of using the traditional test with a cylindrical null screen. This setup of LCD’s has the advantage of display a series of 3 null screens for sampling an optical surface simultaneously, where in the ideal case, the position of the drop-shaped spots should be forming a regular square array of points in the image plane. However, due to typical problems of illumination and directionality with the transmitted light through the LCD's, some spots on the image are missing which complicates the correspondence between centroids and coordinates of the null screens; this is important for the numerical integration procedure used for the quantitative evaluation . In this paper we propose the design of null screens with reference marks, which provide unambiguous correspondence. Specific designs include some strategic color and position coding to ease the image spots identification. We show the method as used during the quantitative evaluation of a spherical steel ball.

The Remote sensing instrument ( RSI ) under developing is a Cassegrain telescope with clear aperture of 450 mm. In order to meet specifications for thermal distortion, self-weight deformation of the mirror and weight budget of the system, the primary mirror has been lightweighted at the ratio about 50 % with hexagon cell structures from a Zerodur blank. For this mid-large lightweight mirror, the optical performance test is challenging during both the manufacture and assembly phases. While in the optical measurement, there are some unexpected errors caused erroneous judgments for the mirror induced by the external force or environmental deviation. For example, it’s difficult to specify the measured astigmatism caused from the form error after polishing or surface deformation by the external force from the supporter or mechanical mount. In this paper, the optical performance test called bench test to get the absolute measurement result for the lightweight mirror is presented. After measurement, a novel algorithm is adopted to analyze the astigmatism caused from the gravity effect and form error from manufacture and the deformation from the mounting or supporter. Also, the measurements with different supporter compared with vertical and horizontal setup are compared in the end of this article.

A new absolute surface metrology scheme based on comparison of transversely-shifted frames from a commercial phase-shifting interferometer (PSI) will work well even when shifts are incommensurate with pixel size. When shifts span multiple pixels, interleaved data sets can, somewhat counterintuitively, still preserve the spatial resolution of component PSI frames, and furthermore non-integer-pixel shifts are easily handled with little loss of fidelity. While obviously useful in characterizing laboratory optics, where the new approach appears simpler and more sensitive than the classical three-flat technique, there are also interesting applications in adaptive optics systems, such as diagnosing non-common-path errors. This and other illustrative applications are briefly described.

Characterizing surface roughness is important for predicting optical performance. Typically, this is accomplished by taking multiple statistically independent measurements and averaging. But, this approach assumes that the statistical distribution of the roughness has a Gaussian (normal) probability distribution. Our analysis shows that this assumption is wrong. Real data acquired from two different sets of telescope optics indicates that roughness of highly polished surfaces is skewed and is best described by a largest extreme value probability (LEV) distribution. Assuming a normal distribution and simply averaging overestimates the most probable surface roughness and could result in the expenditure of unnecessary polishing effort.

In this paper, the cutting effect of Al-alloy using a single diamond turning machining is applied to make on aerospace spherical mirror. The ultra precision cutting has been done in the thermal vacuum chamber and the experimental tryout was minimized using the optimum processing conditions which were determined design of experiments. In this study, we considered three influenced factors on the surface roughness such as cutting speed, feed rate and depth of cut. The purpose of this research is to find the optimum machining conditions for cutting reflector apply the SPDTM technique to the manufacturing of ultra precision optical components of Al-alloy spherical reflector. The cutting force and surface roughness are measured according to each cutting conditions. We achieved the spherical mirror in the 300mm diameter with the surface roughness and the shape accuracy. We also show that the values can be applied to make the Al-alloy spherical reflector using diamond turning machine to perform cutting processing. the abstract two lines below author names and addresses. The abstract summarizes key findings in the paper.