This paper is not a prognostication of the future, but rather a discussion of those aspects of the art, science, and technology of ultraprecision machining of optics critical to the continued development along paths already clearly defined. Visible and near-infrared applications require higher quality surfaces than can be produced ordinarily. The complexity of the finishing process, the materials, the characterization of the resultant surface, and the development of realistic functional specifications are all involved. This paper discusses specific aspects of the problem, including scattered light implications of surface finish/figure, subsurface damage/stability, tool and process improvements, as well as characterization techniques. A substantial effort must be expended in education, as many of the requisite pieces actually already exist--ready to be put into place.

A wavefront corrector (WFC) is a component in an optical system Which corrects for errors of an earlier optic which is imaged onto it. WFC's can be used in two-stage optics in which a primary mirror with large surface errors can be incorporated in the "fovea] mode" to make an ultra-wide-field system and yield an upgraded high acuity image. WFC's, therefore, offer significant cost advantage for fabricating large telescope primaries. We report the JPL-LLNL first embodiment of this concept which includes a non-axisymmetric WFC containing greater than a wave of astigmatism and two waves of coma (1 wave = 0.63 μm). The 6 cm diameter WFC was diamond turned on a super invar substrate covered with 13% phosphorous electroless nickel. Metrology of the WFC with this great an error to 10th wave accuracy was challenging.

Contrast in large flight-simulator screen displays can be significantly enhanced, and power requirements much reduced, by concentrating projected light into a small solid angle around the viewer's line of sight. This is accomplished by the use of a multiplicity of holographic optical elements, all of the same efficiency and of a size below the resolving power of the viewer's eye. If the number of elements is very large, however, automated hologram replication becomes essential. This paper describes the development of a high-gain projection screen consisting of over 10 million holographic elements embossed in aluminized mylar. The design of the holographic master and the replicating technique are discussed.

Single Point Diamond Turning can produce adequate accuracy in figure and roundness for most x-ray grazing incidence optics. It cannot produce adequate smoothness, necessitating the subsequent polishing operation discussed here.

In response to a broad expression of customer interest, Rogers and Clarke Manufacturing Company has recently developed its first-generation CNC spherical generator. This paper presents some theoretical aspects of the design, and some of the obstacles we had to ad-dress. The fundamentals of manual generator setups are well known. The only mathematics involved was to solve a simple equation for the generator head angle, given the rough cutting diameter of the cup wheel, and the work radius to be achieved. Subsequent "cut and try" refinement of the setup is normally an "art" unsullied by mathematical analysis. But the computer requires more precise instruction. Our theoretical considerations, mathematical models, and applications experience are discussed. With the factor of diamond wheel radius wear, it is not possible to finish every lens with computer control. Therefore, the operator of a Rogers and Clarke CNC Spherical Generator has the availability of manual controls for individual machine functions. CNC Spherical Generators are designed specifically for the shop with numerous short runs and perhaps a low diamond wheel inventory. The computer controls system permits much faster setup times, particularly for less experienced operators.

This paper discusses the generation of a scan mirror -- a critical component in a novel Fourier transform spectrometer that is being developed at the Naval Weapons Center. The instrument is a double-beam interferometer that uses rotational motion to change path length. The major component in this interferometer is a scan mirror that is locally spherical but has a continually changing (spiraling) radius. When the mirror is rotated around the axis of the spiral, the path length of one of the interferometer beams is changed. Since this interferometer uses rotational instead of linear motion to change the path difference, very accurate alignment during scanning is possible as well as higher scan speeds. The major drawback is that the scan mirror cannot be made by conventional optics fabrication techniques. The theory and design of the interferometer and scan mirror are discussed. The design details of the machine producing the scan mirror, the actual mirror fabrication, and the preliminary surface evaluation and test of a scan mirror are also discussed.

The slides or carriages used to provide high precision translational motion for measuring machines or optical quality machine tools present special challenges to the design engineer. In order to achieve the extreme accuracy of motion required, a great deal of attention must be paid to the smallest details of the design. This paper will concentrate on the principles of slide design and will more or less ignore the selection of feedback devices and drive mechanisms. Particular attention will be paid to the selection and design of the slideways and their bearings, as these have a profound effect on the performance of the completed mechanism.

The Large Optical Generator (LOG) of the University of Arizona's Optical Sciences Center recently celebrated its second birthday.1,2 During these two years several projects have been completed with the LOG, the most important being the three molds for the Sub-Millimeter Telescope. The accuracies achieved with LOG are discussed as well as the work under way to shift machine operation to a three-axis mode of operation. The use of a toroidal cutting wheel is suggested for solving some problems presented by application of spherical wheels to upcoming work.

Computer Aided Manufacturing, CAM systems for optical fabrication are emerging. As the technology advances optical surface manufacturing will move away from its present labor intensive status and allow the U.S. optical industry to regain an advantage in optical manufacturing. This paper describes a specific CAM Optical Fabrication System, CAM OFS, suitable for the manufacture of spherical surfaces. We also discuss the advantage optical CAM systems present to the optical designer in terms of accurate modeling of a manufactured optical system prior to its actual manufacture.

A new technique for the testing of generalized rotationally-symmetric aspheric surfaces is presented. The technique utilizes commercially available interferometric equipment and unique aspheric compensating components. For each test, the aspheric compensating component is designed as a null reflective end-mirror in the interferometric cavity containing the aspheric surface under test. The aspheric compensating component can be produced by diamond-machining techniques. The design methodology, limitations of the technique and examples are presented.

A non-contacting method is being employed to measure the form of optical surfaces to nanometre accuracy. Slope values obtained by laser autocollimation are integrated with respect to distance to obtain profile height. A single-axis laser profilometer based on this principle was initially developed to monitor profiles along axial generators of conicoid mirrors for x-ray microscopes. The instrument was further modified to enhance the spatial resolution in order to detect surface waviness caused by imperfections in the lapping processes and in the slideways of diamond turning machines. This paper also includes measurement results obtained from a diamond machined optical flat and from silica flats produced by teflon and pitch polishing methods. The instrument has been used further to measure large radii of curvature of spherical mirrors and to investigate the damage caused in a ceramic material when bombarded with a high energy ion beam. A second profilometer is being developed to measure optical flatness over an extended area in two dimensions. The profiles obtained using both instruments along a 50 mm diameter of an optical flat are compared.

The diamond machining machine possesses the attributes of a measuring machine when machining is not taking place. Considering that the disturbances produced by machining will affect the tool workpiece relationship, one may expect this disturbance will disappear when the process is complete. Systematic errors may be eliminated by complementary measurements on the same machine structure in the absence of machining disturbances. In-process measurements may be real time if segregation in the frequency domain is possible. Effective measurements may also be made with little time lag between machining and measuring. Diamond machining opens the process to the use of interferometry on the workpiece as a measuring means. Ordinarily flats and spheres may be checked against easily produced wave front references. Advent of the chordal aspherical generator makes it possible to check aspherical surfaces of revolution in many cases. Examples of in-process configurations and techniques are presented with analysis of the capabilities and limitations which ensue. Key elements are air bearing machine elements, diamond tools, and interferometry with data reduction by micro-computers.

Space-based astronomy at x-ray wavelengths has steadily progressed over the past 25 years. These advances have been made possible through the use of telescopes with increasingly higher resolution and collecting area, along with corresponding improvements in detectors, focal plane instrumentation, and pointing systems. In this paper, we discuss an in-process metrology system designed to provide sufficiently accurate data to the polishing process to allow fabrication of a half-arc second glancing angle of incidence telescope operating in the 1 to 7 KeV spectral region. This measurement system was developed in anticipation of, and applied to, the Advanced X-ray Astrophysics Facility (AXAF) Technology Mirror Assembly(TMA). The metrology instruments represent a considerable advance in the state of the art for measurements of large, thin, aspheric cylindrical optical elements. They allowed measurement of surface figure errors over a very wide range of spatial surface frequency with unprecedented accuracy during each phase of fabrication -- from coarse grinding through figuring and final polishing.

The requirements on figure quality of large optics, particularly in the mid to high spatial frequen-cies have pushed beyond the limits of resolution of some common wavefront analysis methods such as the reduction of interferograms. The smoothness requirement for some large mirrors on spatial scales of a few centimeters can be on the order of 0.01 χ rms, making fabrication and testing of these mirrors difficult. The advent of direct phase measuring interferometry with the use of high density CCD or photodiode arrays can provide the means to achieve the needed spatial resolution.

The nature of the chip formation process during precision diamond turning has been studied via scanning electron microscopy of the chips turned from a polycrystalline copper workpiece. The chip geometry indicates that the material flow is non-uniform and made up of lamellae whose spacing is related to the chip thickness.

Experiments have been performed to measure cutting forces for slow speed turning of aluminum 2024-T361 with diamond tools. A measurement apparatus. was designed and incorporated into an existing precision lathe. Both specimen preparation and cutting force measurements were performed with the lathe. Cuts of 12 mm (0.5 in) in length were made and average forces obtained for a variety of cutting depths, speeds, rake angles, and lubricants. The results of this work show that (a)cutting force and area are linearly proportional to each other, (b)cutting force increases but surface finish improves as the rake angle is varied from 5 to -15 degrees, and (c)cutting force decreases with improved surface finish at higher speeds if a lubricant is used. Finally, agreement between these results and those of a numerical analysis has been achieved.

This paper describes an experimental set-up to perform cutting tests on different materials using single-crystal diamond tools. The method uses a plunge cut into the edge of a rotating disk to approach two-dimensional or orthogonal cutting at realistic cutting speeds. Preliminary results of this method are reported.

An investigation was conducted to develop a set of criteria that would allow the typical user to preselect a diamond-turning tool for the most critical optical finishing operations. A wide variety of tools used in this study had their edge quality evaluated by Nomarski and scanning electron microscopy methods, and the diamond crystal orientation and quality were determined by Laue x-ray methods. One of the tools was subjected to a long-term machining test to evaluate the tool wear process and to correlate the wear observed with changes in the scattering properties of the surface.

Material interactions during use alter the cutting edge of diamond tools and thereby alter tool performance. Commonly observed modes of deterioriation are discussed and related to tool characteristics, to material properties and to the process enviroment.

Wear data are presented for diamond tools cutting electroless nickel (eNi) for cut lengths up to 70,000 ft (13 miles). Two tools having different infrared absorption characteristics were used to cut an eNi preparation that had yielded minimum values for surface roughness and tool wear rate in a previous study. The data include Talystep measurement of the rms amplitude of the feed-marks versus cumulative cutting distance, representative examples of shape changes for the feed-mark profiles, SEM and optical micrographs of the tool rake and flank face wear zones, and measurements of the cutting edge profile and edge recession distance by a tool-nose replication technique. Feed-mark roughness values were found to increase from 5 to 90 A rms over the duration of the test, with an associated edge recession of about 1000 A and the development of a periodic tool edge grooving indicative of burnishing of the part surface. The IR absorption data successfully predicted the order of the two tools in terms of wear rate and fracture toughness.

This paper discusses models for the topographic finish of single-point machined surfaces which involve the randomization or "jittering" of one or more machining parameters. Results are described in terms of the two statistical properties of finish which are important for optical surfaces: its root-mean-square surface roughness and its power spectral density. Analytic examples are presented to illustrate general results and to provide a touchstone for more realistic numerical computations. These results are also directly applicable to the discussion of ruling errors in diffraction gratings.

The design and operation of a near-angle scatterometer that measures the total integrated scatter (TIS) from bare and coated diamond-turned surfaces are described. The scatterometer is designed to make TIS measurements from 0.06 out to 4 deg from the specular beam. Both bare and coated diamond-turned surfaces generated on two different machines were measured. The effect of machine control on minimizing near-angle scatter is discussed.

Surface roughnesses of 1 angstrom rms were measured on low reflectance polished Zerodur and silica substrates by quantitative analysis of Nomarski differential phase contrast images with a fast digital image processor. A measure of roughness was obtained from the standard deviation of intensities in the Nomarski image observed by a vidicon tube with linear response and digitized in real time. The images were averaged over 256 video frames in order to eliminate vidicon noise since the signal-to-noise ratio required to see 1 angstrom roughnesses is 60 dB. Image subtraction was very effectively used to eliminate unwanted intensity variations due to dirt on the surfaces, spurious reflections from optical surfaces and vidicon shading. Work is ongoing to perform the image processing on a generic micro-computer and to reconstruct the surface profiles.