bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical investigation of photonic microwave generation in an optically pumped spin-VCSEL subject to optical feedback
Authors: Huang Yu , Gu Shuangquan , Zeng Yao , Shen Zhenye , Zhou Pei , Li Nianqiang
Published: February 2023

Photonic microwave generation based on period-one (P1) dynamics of an optically pumped spin-polarized vertical-cavity surface-emitting laser (spin-VCSEL) is investigated numerically. Here, the frequency tunability of the photonic microwave generated from a free-running spin-VCSEL is demonstrated. The results show that the frequency of the photonic microwave signals can be widely tuned (from several gigahertz to hundreds of gigahertz) by changing the birefringence. Furthermore, the frequency of the photonic microwave can be modestly adjusted by introducing an axial magnetic field, although it degrades the microwave linewidth in the edge of Hopf bifurcation. To improve the quality of the photonic microwave, an optical feedback technique is employed in a spin-VCSEL. Under the scenario of single-loop feedback, the microwave linewidth is decreased by enhancing the feedback strength and/or delay time, whereas the phase noise oscillation increases with the increase of the feedback delay time. By adding the dual-loop feedback, the Vernier effect can effectively suppress the side peaks around the central frequency of P1, and simultaneously supports P1 linewidth narrowing and phase noise minimization at long times.
Tuning-free and self-supervised image enhancement against ill exposure
Authors: Li Lu , Li Daoyu , Wang Shuai , Jiao Qiang , Bian Liheng
Published: February 2023

Complex lighting conditions and the limited dynamic range of imaging devices result in captured images with ill exposure and information loss. Existing image enhancement methods based on histogram equalization, Retinex-inspired decomposition model, and deep learning suffer from manual tuning or poor generalization. In this work, we report an image enhancement method against ill exposure with self-supervised learning, enabling tuning-free correction. First, a dual illumination estimation network is constructed to estimate the illumination for under- and over-exposed areas. Thus, we get the corresponding intermediate corrected images. Second, given the intermediate corrected images with different best-exposed areas, Mertens’ multi-exposure fusion strategy is utilized to fuse the intermediate corrected images to acquire a well-exposed image. The correction-fusion manner allows adaptive dealing with various types of ill-exposed images. Finally, the self-supervised learning strategy is studied which learns global histogram adjustment for better generalization. Compared to training on paired datasets, we only need ill-exposed images. This is crucial in cases where paired data is inaccessible or less than perfect. Experiments show that our method can reveal more details with better visual perception than other state-of-the-art methods. Furthermore, the weighted average scores of image naturalness matrics NIQE and BRISQUE, and contrast matrics CEIQ and NSS on five real-world image datasets are boosted by 7%, 15%, 4%, and 2%, respectively, over the recent exposure correction method.
Manipulation of sub-terahertz waves using digital coding metasurfaces based on liquid crystals
Authors: Zhang Guozhen , Fang Qirui , Li Ying , Yang Jun , Hu Minggang , Li Jian , Deng Guangsheng , Yin Zhiping , Lu Hongbo
Published: February 2023

This paper presents a novel sub-terahertz liquid crystal (LC) phase shifter based on digital coding metasurfaces. The proposed structure consists of metal gratings and resonant structures. They are both immersed in LC. The metal gratings function as reflective surfaces for electromagnetic waves and electrodes for controlling the LC layer. The proposed structure changes the state of the phase shifter by switching the voltage on every grating. It allows the deflection of LC molecules within a subregion of the metasurface structure. Four switchable coding states of the phase shifter are obtained experimentally. The phase of the reflected wave varies by 0°, 102°, 166°, and 233° at 120 GHz. Due to the presence of the transverse control electric field, modulation speed is approximately doubled compared to the free relaxation state. This work provides a novel idea for wavefront modulation of phase.
Optical Fabrication and Testing of the X-Ray Mirrors for the HEAO-2 Telescope
Authors: Young Peter S.
Published: February 2023

The large X-ray mirrors for the HEAO-2 telescope were shaped, ground, polished, metallized, tested, assembled, and aligned by Perkin-Elmer under contract to American Science and Engineering (AS&E). These X-ray mirrors, when assembled into .their flanges formed the X-Ray Telescope High Resolution Mirror Assembly (HRMA) designed by Smithsonian Astrophysical Observatory (SAO) and AS&E. This paper describes the optical fabrication and testing of these X-ray mirrors.

Particular emphasis is placed on the support of the optics during the three critical fabrication phases: loose abrasive grinding during which the circumferential variation in slope, Δ(ΔR), was achieved; optical testing, during the optical figuring phase; and optical alignment, during final assembly. Also discussed are the optical figuring, surface smoothing via submerged polishing and figure measurement using a semiautomatic fringe scanner and modular interferogram analysis computer programs. The pertinent specifications for the X-ray mirrors and the achievements of the program are summarized.
Scattering and Surface Finish of Unconventional Mirror Materials
Authors: Bennett J. M. , Archibald P. C. , Klugman A.
Published: February 2023

In many systems applications, mirror materials are needed that have, in addition to a good optical surface, high thermal conductivity, light weight, a low thermal expansion coefficient, rigidity, toughness, or other combinations of properties not available in conventional glass or fused quartz optics. Metals, ceramics, semiconductors, and other materials have been considered for mirror substrates. The requirement of an extremely smooth, low scatter surface has spurred a large effort to learn how to polish several unconventional materials, and good results have been achieved in some cases. We will describe in detail the polishing of two of these materials, silicon and molybdenum, and will also mention others. Differential interference contrast (DIC) micrographs and surface profiles of selected materials will be shown, along with rms roughness values obtained from total integrated scattering (TIS) measurements and roughnesses measured directly with a surface profiling instrument.
The Surface Dynamics of Liquid Metal Fusion Reactor Mirrors
Authors: Bacon John B. , Tariello Jean
Published: February 2023

The prospect of using laser-driven nuclear fusion reactions to provide an energy source for electric power generation has resulted in a number of engineering challenges. Not the least significant of these is the so-called "first wall problem," or the extreme thermal and atomic dislocation stresses resulting from the implantation of energetic alpha particles, deuterons, tritons, and x-rays in the top few microns of any solid material directly exposed to the target reaction1. (See Figure 1). While a variety of methods have been proposed1, 2, 3 to protect the structural sections of the reactor from this bombardment, only two options are considered feasible to protect the final optical elements which turn and/or focus the laser beams onto the target.
Diamond Turning Of Aspheric Infrared Optical Components
Authors: Wender David C.
Published: February 2023

Manufacturing infrared optical components, up until the recent past, usually meant optical surfacing by conventional methods. Grinding and polishing have been the primary surfacing processes for both spherical and aspheric optics. Recent advances in both diamond turning and forging of infrared materials is providing a new competitive platform for surfacing which, in turn, is substantially changing design and manufacturing strategies. It is hoped that by informing users of recent advances in diamond turning, forward thinking in the design area will be encouraged. This paper is divided into two parts - a review of diamond turning fundamentals, followed by a presentation of selected turning results in I.R. materials.
Manufacture Of Large Aperture Rear Projection Screens
Authors: Nelson John C.
Published: February 2023

Efficient rear projection systems are made manufacturable by utilizing diamond turning technology and compression molding techniques. Present manufacturing methods allow a variety of refractive surfaces and diffusers to be molded in thermoplastic. Screens can be designed to have specific light distributions that maximize light output into a given viewer space. Use of rear projection for demanding applications such as large aperture television systems is increasing. It is likely that rear projection will continue to replace front projection systems as the cost, performance and size of the rear projection screens are improved.
History Of Replication
Authors: Wahl Harro W. D.
Published: February 2023

Although replication has been around for nearly 60 years, it is still not a very widely known or accepted technique. Outside of replicated diffraction gratings, market penetration of replicated general optics has been marginal at best.
Alignment of Off-Axis Conic Mirrors
Authors: Parks Robert E.
Published: February 2023

The theory and practice of alignment of off-axis mirrors of conic
section are discussed in terms of third order optics. The departure of
a symmetric conic mirror from a sphere of the same vertex radius is
derived. By a transformation of coordinates, this departure is applied
to an off-axis section. It is shown that the off-axis section may be
thought of as a surface containing astigmatism, coma, and spherical
aberration when compared to a bestfit sphere. With this insight, we
show how to determine the location of the optical axis when looking at
the off-axis section from its center of curvature. Once this is known,
the mirror may be placed in an autocollimation test and final
alignment may be performed by observing the shape of the image.
Large Five-Axis Mounts
Authors: Vukobratovich Daniel
Published: February 2023

A mount was designed at the Optical Sciences Center for testing a 750-mm diam, 318-kg center axicon. Several design restrictions were considered: The mount must be capable of translating about three orthogonal axes over a range of 2 mm in submicrometer steps and rotating about two of the above axes in a range of 6 mrad in 0.001 mrad steps. The entire clear aperture of the center axicon must be accessible for testing, and vertical access is required for removal of the axicon from its mount. The mount is to be used atop a vibration isolation system, in a small Class 10,000 clean room, thus imposing size limitations; in addition, the mount must be remote controlled from outside the clean room.
Polishing Rate of Optical Glass
Authors: Izumitani Tetsuro
Published: February 2023

Papers on the polishing mechanism can be classified into wear theory, flow theory, and chemical theory. A fourth concept, based upon the combined actions of the three, is also known. None presents a full explanation of or justification for what occurs during the polishing process, the main reason being that the concepts were developed using only one or a very limited number of glasses; only Kaller used as many as five different types of optical glass. No consideration has as yet been given to the recently developed lanthanum borate glasses, some of which are much harder than pure silica.
Trends in Fabrication of State-of-the-Art Optics
Authors: Parks Robert E.
Published: February 2023

To put the trends in fabrication processes into perspective, it is necessary to look briefly at the requirements of state-of-the-art (SOTA) optics. There is great interest in working toward both shorter and longer wavelength regions. This requirement calls for making smoother surfaces and for greater use of aspherics, respectively. At both wavelength extremes the optics must be reflecting rather than refracting because of the lack of transmitting materials. Other requirements call for optics capable of withstanding high power levels, for larger optics, and for lightweight optics. All these demands have more to do with material properties and mechanical engineering than with optics per se. We will look at the impact of these demands on the methods of optical fabrication.
Observations on Glass Polishing
Authors: Silvernail Walter L.
Published: February 2023

Despite the various theories of the mechanism of glass polishing that have been proposed over the years, there can be little doubt that both chemical and mechanical interactions between the glass surface, the polishing agent, water, and the polishing pad take place. In the following discussion some observations supporting this theory will be presented as well as some other observations of interest to the practicing optician. Before proceeding, however, a word about the measurement of polishing activity is in order. As described elsewhere (1), we subscribe to the belief that polishing of glass involves stock removal and that the stock removal rate as determined by weight is the same whether measured on a fine-ground or on a polished surface. This conviction is based on experiments in which previously fine-ground glass blanks were polished in a sphere machine and corresponding weight loss, thickness loss, and light transmittance measurements were determined as polishing progressed. It is significant that when such observations are made, the weight loss is linear with respect to time; that it remains so during the time the surface is progressing from the ground to the polished state; and that it remains linear after the polished state is reached. On the other hand, the thickness loss as measured with a thickness gauge has a steeper initial slope that decreases with time and finally runs parallel to the weight loss slope after the surface is completely polished. The transmittance measurements increase rapidly to a value of about 90% of that of a previously polished surface used as a standard, and then approach the polished surface value of 100% in a nonlinear manner. Accordingly, these observations and many similar ones made over the years justify using weight loss as a measure of polishing rate, although for purposes of comparison (convenience), we convert the weight loss to a thickness loss by dividing the measured weight loss by the density and the surface area of the glass blank.
Sub-Micron, Agglomerate-Free Aluminas for Polishing Precision Optical Surfaces
Authors: Yancey Paul J.
Published: February 2023

Alumina has been used extensively as an abrasive in the metallographic and precision optical industries. The utility of alumina is derived from its relative low cost, high hardness, chemical inertness, and toughness in lapping and polishing applications. In lapping operations where stock removal and rough shaping are sought, the lower purity, graded Bayer process alumina is used. For final polishing applications, the high purity, submicron, alum derived alumina is generally used. The purpose of this discussion is to point out the general differences between Bayer process and alum derived alumina, and to introduce a new type of alum derived alumina with substantially improved polishing characteristics.
Manufacture of a Reflecting Slit Optical Element
Authors: Page Norman A. , Lam Philip S. , Parks Robert E. , Rodgers J. Michael
Published: February 2023

The requirement for a reflecting slit optical element resulted from design of a visual/IR imaging spectrometer optical system for an earth remote sensing instrument. In this optical system, the reflecting slit is located at the focus of a Schmidt telescope and serves as a field lens, field flattener, and entrance aperture to a two band visual/IR imaging spectrometer. These multiple functions make the reflecting slit a critical element in the optical design. This and concern for the ability to manufacture such an optical element dictated that a breadboard slit be manufacturer and verified before proceeding further with the development of the optical design. The configuration of the optical system is shown in Fig. 1. Unlike the usual spectrometer arrangement, radiation at the focus of the telescope (fore-optic) is reflected, instead of transmitted, by the slit into the spectrometer.
Surface Damage in Cadmium Sulfide
Authors: Hall R.L. , Foschaar J.A. , Gunning W.J.
Published: February 2023

A new type of birefringent filter, called a dispersive birefringent filter (DBF), has been described by Yeh1. A DBF requires a material whose birefringence is dispersive in the wavelength region of interest. In the region from 5300 to 5500 Angstroms (Å), cadmium sulfide (CdS) has this property. Early calculations showed that a DBF made from CdS could be made to have a very narrow passband (approximately 2 Å) and very wide field-of-view (80 to 90 degrees half-angle). At a wavelength of 5320 Å (doubled Nd:YAG) this filter would require flat and parallel CdS plates as thin as 35 microns. When such plates were made, it was found that the absorption coefficient was several orders of magnitude larger than expected. This excessive absorption was traced to mechanically induced surface damage of the CdS. As a result, the ability to produce thin, parallel, and relatively damage-free CdS plates became crucial to the success of the DBF development effort.
Stressed Mirror Polishing of a Two-Meter Diameter Off-Axis Paraboloid.
Authors: Richardson John H.
Published: February 2023

The method of stressed mirror polishing(1,2,3) has been applied during the fabrication of a 2-meter non-axisymmetric segment whose parent paraboloid is nominally 15 meters in diameter. The 2-meter disk of Cer-Vit is a 75mm thick meniscus. This configuration has withstood the applied stressing loads(3) plus ordinary grinding/polishing loads during fabrication.
Interferometric Surface Metrology of Magnetic Recording Materials
Authors: Perry David M.
Published: February 2023

Surface roughness of magnetic recording media has been experimentally and theroetically related to the performance of the media (ref. 1). A computerized three-dimensional interferometer (ref. 2) has become an invaluable aid in the development of current and next generation recording products. Correlations of −0.95 and better are routinely achieved between the measured RMS roughness and magnetic performance measures such as rf output in dB.
Conic Constant and Paraxial Radius of Curvature Measurements, for Conic Surfaces.
Authors: Díaz-Uribe R. , Cornejo-Rodríguez A. , Pedraza-Contreras J. , Cardona-Núñez O.
Published: February 2023

A technique was developed1 to find the profile of a conic surface, along one diameter. In this method it is necessary to - determine a set of values of the longitudinal aberration2, X, - and the corresponding angles, θ. For this method one assumes - that the values of the paraxial radius of curvature, r, and the conic constant, k, are known, and they are related by X = -kz, and tan θ = s/ (r−z(k+1)); where z is the sagitta, and s the distance to the optical axis.
New Stigmatic XUV Plane Grating Devices
Authors: Pouey M.
Published: February 2023

To improve the resolution of grazing incidence XUV devices precise evaluation of the broadening parameters of the Line Spread Function are required. In this respect, transverse ray aberrations must be first evaluated for an oblique exit pupi1-aperture stop not centered al the grating pole-geometrical optical criterion clearly shows then the competitive action of the defect of focus vs astigmatism and astigmatic coma.
A new method for obtaining high resolution mirror figure estimates from interferograms
Authors: Roddier C. , Roddier F. , Richardson J.
Published: February 2023

Obtaining accurate measurements for regions of a workpiece to be tested, spaced closer than about D/25 (D = workpiece diameter) is typically not easy to do with current test methods. Yet, there are occasions when such data would be meaningful. The limitations arise from practical considerations, i.e., how many holes one can put across a Hartmann mask diameter, or how many fringes one can have in an interference pattern and still be able to distinguish unambiguously between them in the digitizing stage, or how many lenslets can be squeezed into a pupil plane array. Of the several approaches, however, improving the analysis of interferograms may be the best approach because all of the workpiece surface is tested at the same time.
Moire Deflectometry Utilizing "ZYGO" Automatic Pattern Processor System
Authors: Sharma D.K. , Delisle C.
Published: February 2023

Moire deflectometry1,2 provides a viable alternative to interferometry for the measurement of ray deflections from a phase object. Being an incoherent technique it is free from stability problems associated with interferometry. Among the other advantages is the simplicity of the setup and use of low quality optics.
Multiple Subaperture Interferometric Testing of Full Spheres
Authors: Williams Rick A. , Kwon Osuk Y.
Published: February 2023

The objectives of this work are to develop nondestructive, optical test techniques to estimate optical path difference (OPD) errors of full spheres (e.g., gyroscopes, ball hearings, micro-balloons). We propose to use a multiple subaperture interferometric test modeled after analogous techniques used in full aperture testing of large optical systems1. A spherical harmonic base set of polynomials for full sphere descriptions is developed, together with the numerical methods for fitting these polynomials to obtain the aberration coefficients over the spherical surface. The physical interpretation of the lower order terms with respect to OPD errors for a spherical body are discussed and demonstrated using three-dimensional graphics representations. A computer simulation of the multiple subaperture technique for full spheres is utilized in an analysis of test accuracy as a function of various test design parameters (subaperture size, number of subapertures, subaperture tilt errors, inter-subaperture phasing errors, etc.). The results of the simulation suggest that optical testing of full spheres is feasable and has the potential for increased speed, accuracy, and surface preservation as compared to direct physical methods.
Microprofiling Precision Optical Surfaces Using Differential Interference Microscopy
Authors: Bristow Thomas C. , Arackellian Kevork , Eastman Jay M. , Bennett Jean M. , Zavislan James M.
Published: February 2023

This paper presents a description of the design and testing of a precision surface microprofiler. The instrument's basic design has been reported at previous conferences (References 1 and 2). This paper will emphasize more specific details of the microprofiler's optical and other system components. Emphasis will be made on describing the elements that influence the resolution of the instrument.
Subaperture Interferometric Testing of Aspheric Optics
Authors: Williams Rick A. , Kwon Osuk Y.
Published: February 2023

Aspheric optical surfaces fill the need to generate non-standard wavefront profiles in many modern optical systems. Interferometric tests have been developed to measure the extreme phase errors, relative to a spherical reference, which occur near the outer regions of the aperture. Several null compensation techniques have been described. For example, a null lens designed to generate an aspheric reference wavefront can be used to negate the effect of the surface figure resulting in measurement of deviations from the desired asphere. Alternatively, computer generated holograms have been used in two-beam interferometers such that the wavefront from the aspheric test surface is compared to a "perfect" wavefront generated by the hologram. A second class of techniques based on shearing interferometry have also been described. For example, a lateral shear interferometer, in which two displaced wavefronts from the same test surface are interfered, does not require compensating optics or a reference surface to measure aspheric figure errors.
Real-time Holographic Phase-Shifting Interferometry
Authors: Creath Katherine , DeVore Scott , Wyant James
Published: February 2023

Holographic interferometry enables the measurement of object deformations due to stress induced by pressure, heat, or applied force. Real-time double-exposure holographic interferometry and phase-measurement interferometry have been combined to measure both static and dynamic changes in objects.1-2 However, quantitative measurements are still not used much in the field of holographic nondestructive testing. Quantities such as fringe density, fringe contrast, speed of data taking, and being able to relate the phase to specific areas of the object have slowed down the spread of this technique. In this paper, we will discuss the state of the art in quantitative holographic nondestructive testing, and show results which we have obtained using our techniques.
Measurement and Analysis of Near Specular Scatter
Authors: Stover John C.
Published: February 2023

Reduction of near specular scatter in optics has become increasingly important in the last few years. Scatter measurement is often confined to the region outside of a 1° or 2° cone centered about the specular beam. Scatter measured as a function angle generally increases without apparent limit as the specular beam is approached. [1] This paper reviews the importance of near specular scatter, examines measurement, and presents some data that illustrates how some of these fundamental limitations can be reduced. Two examples of problems with near specular scatter are presented here.
Some Comparisons of Non Contact Surface Profiling Instruments
Authors: Brown Norman J. , Eickelberg William K.
Published: February 2023

The LLNL, Zygo (mod 5500), WYKO (Topo - 2 D, Topo - 3 D), and Photographic Sciences (MP-2000), non contact optical profilers were compared and found consistent within their common band limits.
Non-Linear Effects in Optical Surface Metrology
Authors: Church E. L. , Feng S. C. , Takacs P. Z.
Published: February 2023

This paper examines non-linear effects which appear in the measurement of surface topography by phase-shifting interference microscopy due to the non-linear relationship between the measured profile, Zm(x), and the true profile, Zt(x). To lowest order this is where P(x) is the point-spread function of the measurement. In an ideal system P(x) = δ(x), the non-linear functions Arg and Exp cancel, and Zm(x) = Zt(x). In real systems, however, P(x) has a finite width which upsets this proportionality. In earlier studies we developed comprehensive models for P(x) by comparing optical and mechanical measurements of smooth surfaces [1,2]. Here we use these models to explore the nature and magnitudes of the non-linear effects which arise in the measurement of rough deterministic and random surfaces for which the linearization of Eq. 1 is not possible. This is done both analytically and via Monte-Carlo simulations.
A Grating Interferometer For Testing The Zone Plate
Authors: Lin J.A. , Yeh W.T.
Published: February 2023

The zone plate is a diffraction optical element which images by interference, rather than by reflection or refraction. The applications of the zone plate include X-ray microscopy, focusing and coupling elements in opto-electronics, X-ray astronomy and etc. The focusing profile of the zone plate has been studied quite well. However, the wavefront aberration of the zone plate was less tested or evaluated by the interferometer1. We use a sinusoidal grating in the Ronchi interferometer to split the wavefront under test into three. The wavefront aberration for both amplitude and phase zone plate may be calculated by taking a few measurements from the three-beam interferograms. The accuracy of the test will be discussed. Since the grating is also a diffraction optical element, it may live together with the zone plate in the region of various radiations.
Metrology of Large Cylinder Mirrors with a Scanning Optical Profiler
Authors: Takacs Peter Z. , Church Eugene L.
Published: February 2023

It is often difficult to measure the figure of cylindrical optics and off-axis segments of conic sections by conventional interferometric techniques. Mirrors designed for extreme grazing incidence applications, e.g., x-ray astronomy or synchrotron radiation beamlines, usually present a highly-foreshortened aperture to a conventional optical test system, making it nearly impossible to interpret the resultant interference pattern. As an end user of a large number of cylindrical aspheric optics, all with different surface figure parameters, and manufactured by a large number of different vendors, the National Synchrotron Light Source at Brookhaven National Laboratory has found it necessary to develop other techniques for characterizing the surface figure of such optical components. In order to be sufficiently versatile to handle a large variety of optical surfaces, we have developed a scanning interferometer system1 based upon the pencil beam interferometer principle2 that is capable of traversing a one meter distance, with a minimum step size dependent upon the laser beam diameter, which is currently one millimeter.
Brittle to Shear Grinding Mode Transition for Loose Abrasive Grinding*
Authors: Brown Norman J. , Fuchs Baruch A.
Published: February 2023

SiC, BK-7 and fused silica were abraded with diamond, CBN and B4C loosely applied. The shear mode behavior is consistent with an elastic penetration model.
Polishing with a Stressed Lap
Authors: Martin H. M. , Angel J. R. P.
Published: February 2023

We describe an actively stressed lap for polishing fast aspheric mirrors to high accuracy. The lap is being used to polish a 1.8-m f/1 paraboloid.
Versatile Profilometer for Aspheric Optics
Authors: Anderson David S. , Parks Robert E. , Shao Lian-zhen
Published: February 2023

In the manufacture of rotationally symmetric optics, it is often cost effective to grind in the asphericity prior to polishing. The larger and faster the asphere, the more this is so. In almost all cases, the aspheric departure from a vertex sphere is a small fraction of the sagitta (sag) of the surface. Since virtually all measuring instruments have an accuracy that is proportional to their total range, a nearly ideal device for measuring aspheric sag would measure just the departure from the vertex sphere.
Fabrication of 2-D Glass Lens Arrays by a Photolithographic Technique
Authors: Borrelli N. F. , Bellman R.H. , Mann L.G.
Published: February 2023

The method of preparing glass microlenses by a photo-thermal process has been described in prior publications. (1-4). In brief, it involves the photonucleation of a phase within the glass. The physical density of the photonucleated phase is larger than that of the unexposed virgin glass. Thus an exposure through an appropriate exposure mask,(opaque dots on an otherwise clear background), followed by heating to 600°C, forms cylindrical regions of soft unexposed glass which are squeezed beyond the surface during the thermal treatment, forming the spherical shaped protrusions.
Fabrication of Large Off-axis Optics
Authors: Jones Robert A.
Published: February 2023

The construction of very large optical telescopes can be prohibitively costly due to the massive weight of conventional primary mirrors. The cost of such telescopes can be reduced by the use of a segmented lightweight primary mirror. An Itek process, computer controlled optical surfacing (CCOS), is ideally suited for manufacturing the off-axis aspheric segments. During CCOS operations, a subaperture tool is moved across the optic surface under accurate computer control. By altering the time that the machine grinds or polishes each surface region, accurate and rapid figure progress can be achieved. This CCOS technology has fabricated seven thin, 2-meter, off-axis, aspheric optics and a lightweighted, active, off-axis mirror. Also, a large active off-axis aspheric is presently being manufactured.
Metrology Cross-checks - a fundamental aspect of the Advanced X-ray Astrophysics Facility (AXAF) Optics Fabrication Program
Authors: Gordon T.E. , Patterson J.S. , Reid P.B. , Zweig D.A.
Published: February 2023

The AXAF observatory is the third of NASA's four planned "Great Observatories"1. It is designed to image cosmic x-rays in the energy regime of 0.1 to 10 keV (124 - 1.24 Å). The mirror assembly consists of four concentric, confocal, Wolter type I telescopes. Each telescope includes two conical grazing incidence mirrors, a paraboloid followed by a hyperboloid.
Ion Beam Milling As Part of a Deterministic Approach to Optical Fabrication
Authors: Egert C. M. , Hylton K. W. , Gooch J. G. , Carnal Charles
Published: February 2023

Ion beam milling is a deterministic optical fabrication process which allows precise control over the removal of material from the surface of an optical component. A deterministic fabrication process is a well characterized and controllable process capable of directly achieving final figure with minimum number of metrology-fabrication iterations. Examples of more deterministic processes are diamond turning and ductile grinding; polishing is considered less deterministic due to the frequent polishing-metrology iterations that are required during polishing. Several investigators have developed and demonstrated ion milling as a deterministic process for glass and glass-ceramic optical components.1,2 While ion milling is more deterministic, it must be used in conjunction with other processes, typically as the final fabrication step, because of its relatively low material removal rates and inability to reduce surface roughness. Early studies of ion milling relied on polishing processes to prepare the optical surface prior to the final deterministic ion milling operation. These demonstrations of ion milling were also limited to amorphous, glass-like optical materials. A complete manufacturing process based on this approach would therefore be limited by the less-deterministic polishing operation. In this paper we present the results of experiments which relied completely on the deterministic processes of single point turning and ion milling to fabricate gold coated, aluminum mirrors. These experiments produced approximately a factor of two improvement in optical figure for both flat and spherical aluminum mirrors in a single ion milling iteration. Besides demonstrating a deterministic approach to optical fabrication involving ion milling, these experiments also indicate that it is possible to ion mill metallic mirrors provided the mirror is overcoated with a material which can be ion milled. The integration of ion milling with other deterministic fabrication processes, combined with recent ion milling-material studies,3 suggest similar highly deterministic manufacturing processes can be developed for many important optical materials including: electroless nickel, silicon carbide, and several IR transmissive optical materials.
Calibration of Surface Damage by the Comparator Method
Authors: Wojtowicz T
Published: February 2023

The growing volume value of trade in optical and opto-electronic components, which is influenced by localised surface quality, has highlighted the need for harmonization of the different approaches for its measurement currently in use around the world.
“Improving the Robustness of Curve Fitting in Figure and Finish Metrology”
Authors: Sullivan Paul , Evans Chris
Published: February 2023

Curve fitting has many applications in topographic characterization including areas such as datum definition, modelling, and filtering e.g. the use of Zernike polynomials in figure metrology and the removal of tilt and curvature in finish measurement. However, topography measurement data does not represent a purely theoretical manufacturing process and contains events which are part of the "true" surface such as scratches and digs (also referred to as pits and troughs or cosmetics), and include erroneous data which are not part of the "true" surface resulting from measurement errors (e.g. signal noise). These events and measurement errors may result in outliers in the measured surface data. The general treatment of outliers is subject to functional considerations but essential to a comprehensive characterization system is the ability to identify outliers and determine their significance on subsequent characterization. Specifically, the presence of outliers within surface data limits the robustness of conventional curve fitting algorithms and thus limits subsequent characterization fidelity.
Modified three-flat method using even and odd functions
Authors: Ai Chiayu , Wyant James C.
Published: February 2023

In a Fizeau interferometer, two flats face each other and form a cavity. The interference fringes detected reveal the flatness of the cavity. In the traditional three-flat method,1,2 the flats are compared in pairs. By rotating the flats with respect to each other, the exact profiles along several diameters of each flat are obtained. A method with more flats and more combinations has been proposed.3 However, with both methods, only the profiles along some straight lines can be solved. Several methods4-8 have been proposed to measure the flatness of the entire surface. These methods involve tremendous least squares calculations. Thus, the fine structure of the surface tends to disappear.
Fixed Abrasive Grinding of CVD SiC to Optical Quality
Authors: Bifano Thomas , Yi Yuan , Kahl W. Keith
Published: February 2023

Chemically vapor-deposited silicon carbide (CVD SiC) is a leading candidate material for large, space-based high energy mirror applications. Because of its large specific stiffness, 99.9999 percent purity, and structural stability, CVD SiC is also being used in less exotic applications, such as in the production of lens molds and replicated optics. Polished CVD SiC is an excellent reflector, particularly for 11-12.5 μm wavelengths [1]. It is, however, an extremely difficult material to polish, because of its low polishing rates (compared to glass). This paper describes a high-precision, fixed abrasive diamond grinding process aimed at eliminating the need for post-polishing for this material. Aside from poor polishing performance, CVD SiC could replace glass in high-technology optical applications because of its toughness, stiffness, and large critical-depth-of-cut with regard to damage-free machining. Table 1 compares some of the relevant material properties of CVD SiC with those of a high-performance optical glass (ULE) made by Coming.
Zerodur Polishing Process for High Surface Quality and High Efficiency*
Authors: Tesar A. , Fuchs B.
Published: February 2023

Zerodur [1] is a glass-ceramic composite of technical importance in applications where temperature instabilites influence optical and mechanical performance. For example, it has been extensively used for earthbound and spaceborne telescope mirror substrates. Polished Zerodur surfaces of high quality have been required for laser gyro mirrors. Recent studies of optics in high power laser applications have indicated that the polished surface quality of substrates affects performance of high reflection coatings [2,3]. Thus, the interest in improving Zerodur polished surface quality has become more general. Beyond eliminating subsurface damage, high quality surfaces are produced by reducing the amount of hydrated material redeposited on the surface during polishing [4]. With the proper control of polishing parameters, such surfaces exhibit roughnesses of <1Å rms. It has been our goal to study Zerodur polishing to recommend a high surface quality polishing process which could be easily adapted to standard planetary continuous polishing machines and spindles. This summary contains information on a polishing process developed at LLNL which reproducibly provides high quality polished Zerodur surfaces at very high polishing efficiencies. A continuation of work is planned to more fully understand the polishing behaviors.
Modeling of interferometric errors in non-null configurations
Authors: Lowman Andrew E. , Greivenkamp John E.
Published: February 2023

Testing an aspheric surface in a conventional phase-shifting interferometer requires use of a null lens to match the test surface. A null lens may consist of refractive, reflective, holographic (CGH) and/or binary optical elements, and it serves to keep the wavefront normal to the test surface.1 Such a null configuration allows the test wavefront to retrace its path through the interferometer, as illustrated by the diverger lens of a Twyman-Green interferometer (Figure 1). Since the diverger lens is corrected for infinite conjugates, no additional aberrations are introduced into the test beam. The time and expense of using a null lens can be eliminated by testing in a non-null configuration, but the test wavefront will no longer retrace itself (Figure 2). Only one zone of the asphere may retrace itself. In Figure 2, the marginal rays are normal to the asphere, but the rest of the reflected wavefront becomes aberrated. These aberrations will change as the test beam propagates through the interferometer optics. The interferometer must then be calibrated if useful measurements of aspheres are to be made. To study the feasibility of calibrating an interferometer for non-null aspheric testing, a Twyman-Green interferometer has been modeled using lens design code.
IN-PROCESS ELECTROCHEMICAL DRESSING: how could you, but the bigger question is should you?
Authors: Polvani Robert S. , Evans Chris J.
Published: February 2023

WHY ? Grinding is, at best, an inefficient cutting process. In general, effective grinding depends on using free cutting wheels - wheels properly graded and preconditioned beforehand and then maintained in-process in a working condition. This is especially true for ductile regime grinding of engineering ceramics. To avoid surface fracture or markings, the 1 to 8 micrometer diamond grit wheels must be kept unloaded with swarf, running true within one to two tenths of a micrometer, and worked using "sharp" diamond grits. Insuring a free cutting wheel from either a choice of wheel grade or the usage of conventional dressing practice is difficult with resinoid wheels and unworkable with metal bonds - bronzes and steels. For ductile regime grinding of glass and especially engineering ceramics - Reaction Bonded SiC, Chemical Vapor Deposited SiC and silicon nitride, we use 2 to 10 um diamond grit, and increasingly rely on electrochemical machined (ECM) metal bonded wheels.
Deconvolution Algorithm Applied to Ion Figuring
Authors: Drueding Thomas W. , Bifano Thomas G. , Fawcett Steven C.
Published: February 2023

An important step in the fabrication of an optical component involves the imparting of a precise contour on the optic, which can be expensive and time consuming. Ion beam figuring is the imparting of a contour on an optical component by removing material through the impingement of a broad beam of accelerated neutral particles, and provides a highly deterministic method for the final precision figuring (or correcting) of optical components with advantages over conventional methods. The high predictability allows the possibility of single step figuring, resulting in significant time and cost savings. And unlike grinding, polishing and lapping, ion figuring is non-contacting and so avoids several problems including: edge roll off effects, tool wear, and loading of the work piece. It has previously been demonstrated that ion figuring is effective for the correcting of large optical components [1][2]. The work discussed here is directed toward the development of the Precision Ion Milling System (PIMS) at NASA's Marshall Space Flight Center, designed for the processing of smaller (8 cm diameter) optical mirrors.
Polishing Studies to Achieve Supersmooth Finishes on Convex Single Crystal Silicon Optical Components
Authors: Gunnarsson Gunnar , Platt Royce L.
Published: February 2023

The ability to grow large single crystal silicon substrates and their potential applications in high energy laser systems has provided the need for application of advanced fabrication capabilities to this material. Diamond turning, diamond grinding and other non-conventional fabrication methods for piano and aspheric optics are candidates for processing single crystal silicon. Diamond turning of such materials1,2are providing an economical means of producing these optics.
Evaluation of Bound Abrasive Media for Fabrication of Ring Tool Polishers
Authors: Ng W. , Puchebner B. E. , Jacobs S. D. , Currin J. L. , McAvoy B. , Yungk D. , Gracewski S.M. , Funkenbusch P. D.
Published: February 2023

The objective of this research is to develop a ring tool polisher for deterministic finishing of optical glass parts on Opticam® machining centers at the Center for Optics Manufacturing (COM). To be successful, the ring tool must reduce rms roughness from 100-200Å to 10-20Å, remove 2-4μm of residual subsurface damage, and preserve the surface figure of the glass part. The medium used to fabricate the polisher must satisfy several criteria. It must contain and be able to release polishing agent to the glass surface in an aqueous environment. It must be capable of being formed or machined into a ring (solid or segmented) with a sharp edge. It must maintain its physical integrity at high tool velocities without exhibiting catastrophic failure under load, and it must not show excessive wear during use. It must not require the assistance of additional polishing slurry. These are formidable requirements.
Fabrication of optical surfaces by laser pattern generation
Authors: Bowen John P. , Blough C. Gary , Wong Vincent
Published: February 2023

In contrast to conventional optical fabrication techniques, a single-point laser pattern generator (LPG) provides a flexible, deterministic method of manufacturing optical components with a microrelief pattern. The generated elements function by diffraction and interference effects resulting from light striking a micro-structured surface. The structured or diffractive surfaces can be designed with commercially available lens design software.
Predicting the effects of vibration in phase shifting interferometry
Authors: de Groot Peter
Published: February 2023

The objective of this study is to find an analytical means of calculating the measurement error in phase-shifting interferometry1 (PSI) due to mechanical vibration. The mathematical approach is inspired by linear systems theory and Fourier methods recently developed by Freischlad and Koliopolous2 and by Larkin and Oreb.3 The sensitivity of the interferometer to vibration is reduced to a phase-error transfer function, which includes such factors as the data sampling characteristics of the PSI algorithm, the video camera frame rate and integration time.
Nanometer Sized Alpha Alumina Polishing Slurry
Authors: Rostoker David
Published: February 2023

Seeded Gel (SG) abrasives have made a major impact on traditional abrasive applications. The structure of SG is one of 100 to 300 nm crystallites tightly sintered to a zero porosity polycrystalline α - alumina body.
New Developments in Bound Abrasive Polishing of Optical Glass on Opticam® Machining Centers
Authors: Gillman Birgit E. , Jacobs Stephen D. , Snyder Shane E. , Atwood Mark A.
Published: February 2023

Several in-house bound abrasive polisher compositions have been developed which remove subsurface damage (SSD) and reduce the rms microroughness of a variety of optical glass types to ≤10 Å in a 30 minute polishing cycle. The polisher manufacturing method is consistent and reproducible.1 The majority of the work to date has been done on a single spindle machine by polishing flat optical glass parts against a molded pellet lap using deionized water as the coolant.1,2 Recently, the Opticam®SX machining center at the Center for Optics Manufacturing (COM) became a second experimental testbed for evaluating polisher performance. The machine was utilized for evaluating polishers of the same composition as the molded pellet polishers, but in the ring tool configuration. Surface microroughnesses of <10 Å rms were obtained on BK7 glass. A new polisher formulation also removed the cutter marks which are typically introduced during the grinding cycle. The ring tool polisher was used as the last tool in a series of automated tools for final finishing of a microground lens surface.