Most equipment used for the machining of diamond turned optical components is developed using custom designed components. These components include spindles and slides which are created specifically for the design at hand. They have no other application. Careful design can, however produce machine components which have many uses without any sacrifice in performance. In fact, by designing modular slides and spindles with an eye towards a number of potential applications, the overall performance of these devices can be improved. An example of this is a new, multi-axis diamond turning machine which uses modular construction and has a resolution of 1.27 nanometers. This machine has two identical hydrostatic slides which can be assembled in a number of configurations to create different machines. The work spindle can be used as a flycutting spindle or as the wheel spindle on a grinder.

Applied Physics Specialties, a small optical component manufacturer has invested in a diamond turning machine. This article reviews the reasons for obtaining the machine, staff preparation and selection, site preparation, a discussion of the initial work plan and a listing of miscellaneous equipment required.

Commercially available diamond turning machines offer high levels of accuracy where the full potential of the machine is realised. Unfortunately, surface form accuracy and roughness are dependent on the limiting stiffness of the machine/workpiece environment. Vacuum chuck methods offer a high degree of stiffness combined with the opportunity of mounting substrates in a stress free manner. Thin substrates (4-12 mm) are relatively easily stressed and the application of vacuum chuck mounting for such components, present many problems. These include deformations due to internal material stress, vibration, and the print-through effect. We have measured the reproducability of deformations caused by the print-through effect and have developed techniques for its elimination. The feasibility of using this print-through mechanism for machining non-rotationally symmetric forms is also discussed.

This paper outlines the underlying philosophy of, and reports preliminary results from, experiments with three nominally identical diamond turning machines. Identical tools,specially fabricated from the same diamond, were used to machine mirrors from blanspks cut from the same base material using previously specified process parameters; parts produced are compared.

The manufacturing processes used to refine the surfaces of large annular conical mirrors began with the application of a nickel plating to machined substrates, proceeded through diamond-turning, and concluded with polishing operations establishing fractional wave-length accuracy. The task of polishing such surfaces required the construction of specialized equipment and the application of procedures which would assure the preservation of an established radical aspheric contour, yet allow the removal of those errors remaining after completion of the previous diamond-turning operations. These requirements were met by the application of polishing machines employing flexible belts, and the various errors encountered on the asturned surfaces are discussed and classified by spatial frequency. The presence of significant azimuthal errors led, ultimately, to the development of a dual-head belt polishing machine having a computer-controlled rotary table. This device allowed automated removal of azimuthal errors by varying angular velocity of the table so as to apportion dwell time of the polishing heads according to the azimuthal profile. The application of the computer-controlled belt polishing machine to the correc-tion of non-axisymmetric azimuthal errors, and the results obtained, are presented.

The purpose of this project is to produce a generic high precision computer numerical controller (CNC) for use on microinch- and sub-microinch-resolution machine tools at the Lawrence Livermore National Laboratory. In order to fully utilize the potential of these machine tools, the CNC must include the ability to use multiple feedback sensors on each machine axis, incorporate corrections for quasistatic geometric errors (such as straightness, and squareness), be able to function over a relatively large range of motion (in excess of 60 inches per axis), and be able to produce motion updates at a rate sufficient to take advantage of the high bandwidth of the servo systems. At present, no commercially available CNC can presently meet all of the resolution, feed rate, and length of travel requirements of these machines. In order to minimize the complexity of the system, and thereby increase its reliability and maintainability, the programming was done in a high level language. The number of processors was kept as small as possible while still maintaining the performance requirements. We also used commercially available hardware in preference to building, in order to increase both reliability and maintainability. Special emphasis was given to making the CNC's operator interface as friendly as possible. We have completed a prototype control. We plan to install and test it in 1988.

One of the most challenging optical components to fabricate is a non-axisymetric part. We at Lawrence Livermore National Laboratory recently used the Large Optics Diamond Turning Machine, (LODTM), to make a part called a phase corrector. The Phase corrector is an annular opical component that is used to generate a known spectrum of time varying aberration. If the corrector has the proper distribution of spatial frequencies and amplitudes it will function correctly. Since the frequencies and amplitudes were the important requirement on the surface figure, the surface of the part was specified in the Fourier domain. A surface profile was generated from the spectrum which contained spatial frequencies as high as 40 cycles per revolution. The spatial frequency maps into a time domain frequency for the z- axis tool bar that is dependent on the spindle speed. At 40 cycles per revolution, any reasonable spindle speed taxed the band width limits of the z-axis tool bar. In order to decrease the errors in the surface figure due to machine dynamics, a technique for compensating for the dynamics in the Fourier domain was developed. The non-axisymetric phase corrector was directly machined out of brass on the LODTM. Test measurements of the surface figure were made with an LVDT on LODTM and compared to the commanded profile both in the spatial and frequency domains. The surface quality was measured with a Wyco Model 1000P surface analyzer.

Over the last decade a wide variety of processes applicable to ultraprecision contouring and polishing have evolved. Examples of these processes include float polishing, elastic emission machining, erosive jet, ion milling, plasma assisted chemical etching, and precision ductile grinding. These processes are reviewed with the intent of comparing their removal rates, resultant surface roughness, demonstrated contour accuracy, and applicability to the manufacture of large optical components. The incentive for this study is the evolution of a deterministic manufacturing process able to lower the cost of fabricating large precision optical components by an order of magnitude.

During recent years, economic and technological pressures have driven research for higher performance optical fabrication techniques. Among the candidate figuring technologies is ion beam sputtering in which material is removed from the optical surface by the kinetic interaction of ions and atoms or molecules of the surface. The first use of sputtering as a means for optical figuring occurred in the mid 1960's [1,2], and the technique has been investigated by several groups since that time. The prior work was done primarily with ion sources producing high energy (20KeV and above), low current (fraction of a milliampere), narrow (usually less than one millimeter) ion beams. The low current directly translates to low removal rates, while the high energy contributes to radiation damage, ion implantation, and other effects. In the present work the low current, high energy source is replaced with a Kaufman broad-beam ion source[3]. These sources produce higher ion currents at lower energies, thus giving faster removal with minimal surface damage. The ion beam produced by a Kaufman ion source consists of a number of ions traveling in a (typi-cally) slightly diverging beam, along with an equal flux of lower energy electrons. The electrons are injected into the ion beam to reduce electrostatic repulsion in the beam, but also to prevent the charging of dielectric targets.

We present experimental results of an ongoing investigation demonstrating that Plasma Assisted Chemical Etching (PACE) can rapidly and controllably figure and smooth optical surfaces without mechanical contact; thus, removing the constraints on the design of optical elements imposed by mechanical processes, and, allowing higher quality optical surfaces. This process employs a plasma etch process originally developed to pattern micro-electronic circuits by etching through a relatively non-erodable lithographically patterned mask. The PACE process shapes the optical surface by removing material in a small area under a confined reactive gas plasma moved over the surface. Rates of removal as high as 10 m per minute are obtainable with accurate control. The removal footprint can be varied during the process. PACE inherently smooths or polishes while removing material, exposing a virgin surface free of process generated contamination and subsurface damage. Although other materials can also be figured by a PACE process, for this study, apparatus and processes were developed to explore the figuring of fused silica. Results will be shown demonstrating: repeatability and control of removal rate and footprint; predictability of material removal with plasma "tool" motion; and smoothing.

We describe an application of Plasma Assisted Chemical Etching (PACE) to rapid and controllable figuring and smoothing of optical surfaces without mechanical contact. This removes the usual constraints on the design of optical elements imposed by mechanical pro-cesses, such as substrate deformation, edge distortion and subsurface damage or contamination. This process employs a process originally developed to pattern microelectronic circuits by ion enhanced chemical etching of a solid (Si02, Si, Al, Au, etc.) through a relatively nonerodeable photolithographically patterned mask1,-2. The PACE process shapes the optical surface by removing material in a small area under a confined reactive gas plasma (a "puck") moved over this surface. Rates of removal of such processes in microelectronic applications are as high as 10 pm per minute and are very accurately controllable and repeatable. The removal "footprint" of PACE may be varied during the process and it inherently smooths or polishes while exposing a virgin surface free of process generated contamination and subsurface damage. It can operate in two modes: (1) in "contact" with the plasma, where the chemical reaction is driven by the kinetic energy given up at the reacting surface by short lived species such as ions; and (2) downstream of the plasma, by the stored energy freed at the surface by longer lived species such as excited metastable neutrals. Since control of this process is so important to this application, we sketch the generic physics and chemi hi stry1,2 of the PACE figuring and smoothing process, identifying the quantitative relations between the plasma and chemical parameters that control it:rf power density reactive gas pressure reactive gas flow the reactor surface temperatures and the pertinent transport chemistry.

We study the smoothing behavior of PACE using a differential equation which describes the temporal evolution of a solid surface subject to any etch (or deposition) process. The differential equation explicitly exhibits the evolution of any surface to be a product of a geometric factor, common to all such processes, and a rate factor that depends on the process physics. We take the rate factor to be a combination of isotropic and anisotropic processes. In general, it must be derived from first principles or deduced by comparing the topography predicted by the surface evolution equation with the observed etch topography for a particular physical hypothesis. An example of this is shown for the etched shape of microelectronic "deep isolation trenches" fabricated by a purely anisotropic process. Good agreement with observation is achieved when the rate coefficient is taken to have a local surface curvature or local electric field dependence. Finally, the surface evolution equation is used to explore the ability of PACE to smooth and polish an initially rough surface by obtaining the time dependence of the spatial Fourier coefficients of the surface shape from the differential equation. This analysis provides a vivid exposition of the PACE smoothing process. Both the anisotropic and isotropic etching regimes of PACE are considered.

Ductile-regime grinding is a new technology made possible by the use of real-time control and precision engineering in the grinding process. By ensuring that the abrasive grinding forces do not exceed a threshold value, it is possible to grind materials that are normally considered "brittle" in such a way that the material removal takes place through plastic deformation rather than fracture. The material surfaces produced by ductile-regime grinding exhibit excellent contour accuracy along with surface finishes that previously could only be achieved through polishing or lapping. This paper describes an analytical and experimental investigation of the machining parameters and material parameters that influence grinding ductility.

There is an ongoing need for economical, lightweight, stable mirror substrates which are capable of high optical performance in the visible and the infrared. Metal matrix composite (MMC) materials were selected as one class of materials suitable for meeting such needs. The economical fabrication of MMC materials into lightweight mirror structures requires unique machining and heat treating methods. These methods were developed for the fabrication of a high quality MMC lightweighted mirror which is described below.

The purpose of this paper is to provide a basic understanding of the fundamentals and uses of ultrasonic impact grinding (UIG) and how it can apply to the fabrication of optical components. Emphasis will be placed on the basics of UIG, examples of applications, and capabilities of the machine tools available. Because UIG has the capability to generate complex 3-D shaped in virtually all hard, brittle materials, it has many applications in the fabrication of optical surfaces as well as heat transfer surfaces in high energy components.

In typical interferometric testing the part under test is measured against a reference standard. The measured result is the difference between the errors in the test and reference surfaces plus any additional errors introduced by the interferometer. For accurate qualification of the reference surface it is necessary to employ a technique that can measure the part absolutely. This paper examines an existing technique) for absolute testing of spherical surfaces which produces a map of the entire surface. The capabilities of this technique, error sources, and experimental data will be examined.

The precision machine tool industry has developed processes that produce rotationally symmetric surfaces, both spheres and aspheres, with form errors on the order of 5 microinches (1/5 wave or 0.125 p.m). Precisionmachined diamondturned surfaces can have surface finishes better than 100 angstroms Ra; these surfaces may be intended to be used as an optic, or the surface may be intended to be used to meet a mechanical requirement. Regardless of their intended use, surfaces of this quality can be tested using optical test techniques such as interferometry. This paper reviews the advantages and disadvantages of the methods that have been used to measure aspheric surfaces in the Aspheric Technology department of Kodak Apparatus Division. These techniques include Fizeau and Williams interferometry, holography, stylus and optical profilometry, and null correctors.

Over the past few years the Aspheric form has become a commonly used geometric shape, primarily in the optical industry for components such as contact lenses and compact disc laser focusing optics. This paper discusses the function of an aspheric measuring system and highlights applications where it's unique capabilities alleviate previous metrology problems. In addition an indication will be given as to how by . the use of interactive feedback, significant improvements can be obtained in the accuracy of the fmished component

Recent advances to the WYKO TOPO-2D and TOPO-3D surface profilers provide new analysis techniques for the measurement of diamond turned surfaces. Very high spatial resolution is made possible by the introduction of a phase shifting Linnik interference microscope objective where spatial resolutions less than 0.5 μm and height resolutions of less than 0.01 nm are possible. Additional new software has been developed to analyze localized slopes, power spectrum, and roughness along and perpendicular to the lay. Analyses of diamond turned samples measured at 200X are included.

A simple system geometry using a low power laser has been designed to measure the surface curvature of a lens or a mirror or the refractive index of a slab of a transparent material by using the Fresnel reflection from its surfaces. By comparing our measurements of the surface curvature to those using a precision spherometer, we found this method accurate to ±0.1 mm for curvatures from 25 to 75 mm. If the thickness of a parallel plate can be measured, this technique can determine the refractive index of the plate without resorting to demounting or cutting a sample to be measured. Measurements of fused and crystalline quartz flats determined the refractive indices of the samples to ±0.001. The application of this technique to in situ measurements of optical systems and its limitations will be discussed.

A scanning CO₂ laser interferometer is described, in which the test sample itself forms the interference cavity. Results for plane parallel plates of germanium and of galliumarsenide are presented and discussed. Samples with perfectly plane surfaces allow to evaluate the uniformity of the refractive index across the sample.

A design philosophy for polygon scanners is described. A scanner is designed as a whole rather than simply specifying a polygon which is attached to a standard motor and bearings. The following components are considered: bearings, polygons, housings, motors and synchronisation devices. Methods of production and testing are described. The assembly methods are outlined, particularly those that can reduce the effects of misalignment, distortion and even the component errors themselves. Finally, the testing of the complete scanner is described.

A system to measure the static geometric slide errors of a Coordinate Measuring Machine is described. The system uses a 36" x 36" optical reference flat and four plane mirror interferometers to measure the six possible components of rigid-body motion of the machine probe relative to the machine table. Multiple traces are taken in each of the 3 axis directions to produce a map over the measurement volume. Error compensation techniques based on the interpolation between traces to enhance accuracy are discussed. An auxiliary method is described which is used to measure slide axis squareness. The error map is then adjusted for slide squareness. The control or compensation of sources of non-repeatability and its impact on mapping and compensation accuracy is also discussed.

An array of four telescopes has been fabricated to sufficient precision and stability to serve as a testbed for phased array imaging experiments over a wide field of view. The overall optical and mechanical design philosophy is given as well as the analysis of fabrication and assembly tolerances. Finally the fabrication, assembly and alignment methods are described.

This paper will review some applications of design and manufacture that allow an optical fabricator to incorporate functional mounting, alignment, and test surfaces into diamond turned optics. A design example has been manufatured to demonstrate the concepts presented in this paper.

This paper presents the results of diamond-turned surfaces of a wide range of aluminum alloys. The alloys machined included a sand-cast A201 alloy manufactured by Specialty Aluminum Inc., conventionally extruded plate alloys 2024, 3003, 5052, 6061, 7075, and for comparison as a best and worst case possible a high-purity aluminum single crystal, and tooling plate. The surfaces were obtained by diamond single-point machining using an interferometrically controlled two-axis, air-bearing lathe. The effect of tool-rake angle and machining fluid on surface quality is examined. Surface characterization was performed by Nomarski microscopy and noncontact optical surface profilometry. The optical properties measured included absolute reflectance at 3.8 μm, total integrated scatter at 752.5 nm, and bidirectional reflection distribution function measurements at 632.8 nm. The dimensional stability of the aluminum alloys subject to thermal cycling is examined.

Attenuation screens of different types are used frequently in interferometer cavities when one wishes to control the intensity of one arm with respect to another arm, to achieve good fringe contrast. A study of attenuation screens for use in interferometer cavities was performed to determine the optimum attenuation screen mesh frequency, orientation, and cavity location, theoretically and experimentally. A commercially avaliable Fizeau type interferometer was used for the investigations. Screen frequencies of 500, 400, 325, 230, and 100 wires per inch were used. Experimental results with these screens of different test configurations are presented. The durable, inexpensive, and versatile attenuation screen provides an excellent alternative to coated or metallized pellicles used as attenuation filters.

The need for increasingly larger diameter mirrors is met by using segments to build up a large mirror surface. The segmentation of the mirror surface results in the deterioration of its optical properties, most notably those caused by the diffraction effects. The presence of the segments also introduces the additional complexity in the mirror assembly and alignment procedure. A precise segment alignment is based on the optimization of the Strehl ratio for the segment using a laser beam. An expression for the Strehl ratio for an off-axis square parabolic segment is obtained. It is shown that a segmented mirror is most effectively utilized in an optical system with a large F-number.

Creep and strength of candidate glass contact refractories for honeycomb casting molds were measured at 1200 C. Based on performance and cost, one material, Rex Roto Corp.'s R1162-17 speciality fiber mix, was chosen for the Steward's first 3.5m casting mold. More extensive measurements of firing shrinkage, thermal expansion, room temperature Young's Modulus, bulk density, and creep were carried out on R1162-17 samples cut from hexagonal box preforms. Test results indicate that R1162-17 hex boxes have acceptable creep resistance and the potential strength to withstand hydrostatic loading up to 66cm of borosilicate melt. In November of 1987, blocks of a low-expansion borosilicate glass, Corning Code 7761, was spin cast into a 1.2m honeycomb for the Smithsonian Astrophysical Observatory. The casting contained a relatively high density of small-scale striae and small bubbles along the remelted block surfaces. Origin of the small bubbles was traced to graphite particles imbedded in the glass surface during the forming operation. In spite of small-scale striae, the measured expansion coefficient variation over spacial scales greater than 1mm was less than t7x10-9/C.

For use in large mirrors in outer space, where low mass is a critical need, 3 D-CFK developments are under our investigation since 8 years. Precision replication future technologys taken from a negative form are our candidates for the ESO, VLT monolithic primarys. In our option we use a Nasmyth Focus, because of mirror stability.

Low expansion glasses offer many advantages as mirror blank materials due to their thermal and mechanical properties as well as the flexility they offer in design and fabrication. Fused Silica, Corning Code 7940 and ULE titanium silicate, Code 7971, produced by the flame hydrolysis process, are high purity and homogeneous glasses. Determination of the average and the variation pattern of ghe Coefficient of thermal expansion (CTE) within ULE mirror blanks (nominally 0 x 10 /°C over the 5°C to 35°C temperature interval) is readily accomplished to an accuracy of + 2 parts per billion per degree centigrade (ppb/°C) by ultrasonic measurements. The ability to fusion seal each of the glasses offers mirror manufacturing design freedom of shape, size and weight. Solid monolithic mirror blanks have been successfully manufactured by the hex-seal method up to 4 meters diameter and 10 meter blanks are an extension of the proven fusion techniques. Lightweight fusion bonded ULE mirrors, such as the primary used in the Hubble Space Telescope, are fabricated by first "welding" selected glass pieces together to form a structurally rigid core and then fusing it between two plates. Ultralightweight (10% solid weight) low expansion mirrors produced by "frit bonding" a fusion core between two precision machined plates, maintain an optical figure when exposed to thermal cycling and mechanical abuse environments.

A 3.5 meter diameter, f/1.75 focal ratio, telescope primary mirror blank was spuncast in May 1988. This paper describes the materials, processes, and methodology used to construct the mold which shaped this lightweight honeycomb borosilicate mirror.

A 3.5-meter-diameter telescope primary-mirror blank was cast from E6 borosilicate glass at the University of Arizona, Steward Observatory Mirror Lab. A light-weighted-hollow design was made with a faceplate and backplate separated by a middle volule of ribs in a honeycomb pattern. The curvature of the F/1.75-mirror face was formed by spinning the melted glass at 8.54 RPM. A telescope on Apache Point in New Mexico will use this mirror.

Hextek Corporation is an optics design and manufacturing firm located in Tucson, Arizona. Our primary efforts have been in the refinement of our Gas Fusion process that renders lightweight mirror blanks in a fraction of the time required by conventional methods. Our borosilicate lightweight mirrors have found applications in large laser systems, astronomical telescopes, and system test benches. This paper describes the design and construction of an 84 cm Gas Fusion, center-plane-mounted, secondary mirror blank. This blank was purchased by the Astrophysical Research Consortium for incorporation into the 3.5 meter telescope located at Apache Point, New Mexico. Work on the secondary began in May 1988 and was completed the following month and then delivered to an optics shop for generating and polishing.

A general method of analyzing fringe data from interferometric testing of optical surfaces is described. The method combines the surface optimization routine with the lens design software to simulate the optical testing and to reconstruct the testing surface. With this method the residual error requirement on null lens design may be relaxed; some alignment ambiguities can be removed; and the final surface figures and tolerances can be defined. Sources of error are discussed.

In late December of 1987, the Optical Sciences Center at the University of Arizona completed a seventh primary mirror for the Multiple Mirror Telescope (located on Mt. Hopkins in southern Arizona). The spare mirror allowed astronomers to maintain a six-mirror configuration while one mirror was down for realuminizing or when repairs to its support system were being carried out. Weather at the southern Arizona site is so ideal that a higher-precision mirror was needed to take advantage of these atmospheric conditions. 'When the specifications were considered, it became apparent that standard fabrication techniques would have to be altered somewhat to achieve a successful mirror. The problems considered were print through, or quilting of the mirror's ribs onto the optical surface, the possibility of astigmatism developing (tests indicated the blank lacked uniform strength across the back), and the necessity to maintain a precise focal length.

The figure-quality specifications for the seventh Multiple Mirror Telescope (MMT7) mirror were unusual in that they were defined in terms of rms differences. Recognizing that the atmosphere can be the limiting factor in telescope performance, the specifications for the MMT7 mirror, a 1.8-m, f/2.7 parabola, were derived from analysis of the wavefront irregularities induced by the atmosphere on a nominally perfect planar wavefront from a star. This approach to mirror specifications apparently was first taken with the 4.2-m Herschel Telescope primary mirror, fabricated at Grubb-Parsons.

Numerical analysis and simulation of simultaneous determination of misalignment and mirror surface figure error of an optical system (three mirror off-axis telescope) by Hartmann ray measurements and reverse optimization (without using any special auxiliary optical component) were carried out. In the Hartmann method, a laser beam was shone through Hartmann holes into a roughly aligned optical system from several different angles (multiple fields) to separate misalignment of each component (mirror) from the others, and several separated detection planes around focus were used to measure both the relative ray positions and relative ray angles. The measured relative ray positions and relative ray angles were fed into a optical system optimization routine (ACCOS V) as optimization targets. Then, the optimization was set forth starting from the ideal optical system defined in the design prescription to find the final best-fitted optical system to the measured ray data by varying alignment and mirror surface figure variables (tilts and separation of each component and detecting plane and spline function of mirror surface figure). The optical system best-fitting the measured ray data shows misalignment and mirror surface figure error of the optical system under test. The numerical analysis and simulation showed that the combined method of the Hartmann technique using multiple fields and multiple detecting planes and the reverse optimization using both the ray positions and ray angles as optimization targets provides a very reliable (large capture range and no trapping in a local minimum during optimization) and easily realizable (measurement tolerances are quite large) way for the simultaneous determination of misalignment and mirror surface figure error of optical system without using any special auxiliary optical component.

A new long-trace optical profiling instrument is now in operation at Brookhaven National Laboratory measuring surface figure and macro-roughness on large optical components, principally long cylindrical mirrors for use in synchrotron radiation beam lines. The non-contact measurement technique is based upon a pencil-beam interferometer system. The optical head is mounted on a linear air bearing slide and has a free travel range of nearly one meter. We are able to sample surface spatial periods between 1 mm (the laser beam diameter) and 1 m. The input slope data is converted to surface height by a Fourier filtering technique which distributes the random noise error contributions evenly over the entire trace length. A number of optical components have been measured with the instrument. Results are presented for fused silica cylinders 900 mm and 600 mm in length and for a fused silica toroid and several electroless nickel-plated paraboloids.

We recently had two occasions to qualify optical flats of moderate size. Because of the mounting geometry, it was convenient to try measuring them with a Fizeau test against a liquid surface. In a preliminary literature search, we found few writings on the application of liquid flats. In this report, we briefly review the literature before describing our experiences and results.