Substantial improvements in the properties and performance of optical coatings have been obtained by retrofit of a 96-inch vacuum evaporation coating chamber with a high-current, low-voltage ion gun for ion-assisted deposition. Improved optical coatings for large laser optics, astronomy mirrors, or batch production of small or midsize optics are now available, without the need for substrate heating. This paper presents the technical approach and the earliest results for recent successful ion assist implementation in Itek''s largest coating chamber. Optimal use of ion assist in harmony with the evaporation process is described, and chamber geometry, ion gun installation, and related technical issues are briefly discussed. Property enhancement data are presented for several classes of coating materials, including oxides, fluorides, and sulfides. Improvements in refractive index, density, abrasion resistance, adhesion, mechanical stress, and stability to temperature and humidity exposure are included. Results for large optics coated to date are presented

Programmed motion of a tool which removes material by plasma assisted chemical etching (PACE) gives controlled, deterministic figuring. The process has been automated to correct arbitrary figure errors on aspheric surfaces directly from the measured surface data. A system is now operating for figuring aspheric surfaces up to 0.5 m diameter. PACE can greatly reduce the time and cost of figuring large optics by its rapid convergence to the final figure requiring only two to three measurement/figuring cycles to reach 1/50 wave surfaces. PACE intrinsically smooths high frequency roughness with material removal leaving a surface free of subsurface damage

Plasma assisted chemical etching (PACE) and ion milling (IM), originally developed for microelectronic fabrication, are now finding a new use to shape (figure) and smooth (polish) optical and other surfaces without mechanical contact. Using a recent theory of the temporal evolution of surfaces during arbitrary additive or subtractive processes, the predicted and observed smoothing of PACE and IM are critically compared in this paper to provide insight into their fundamental behavior

The National Optical Astronomy Observatories has been working to extend existing fabrication techniques necessary to polish and figure large, steeply curved, structured borosilicate glass mirrors to exceedingly close tolerances. This paper describes the generation, grinding, and polishing techniques used to transform a 3.5 m diameter, f/1.75, glass casting into a precision spherical surface. The accuracy of the finished sphere was 0.52 (lambda) peak- to-valley and 0.066 (lambda) (42 nm) rms

The stress polishing technique is a powerful tool for fabrication of off-axis mirror profiles. The inherent smoothness that can be achieved from polishing spheres can now be applied to asymmetric profiles. This smoothness, combined with the need for the mirror to be thin and flexible, can be coupled to active mounting systems which readily correct low order shapes to produce a near ideal system. This technique will allow the fabrication of complete off-axis telescopes within the same basic cost range as on-axis systems, if not for less. The strength of this statement comes from the fact that both the primary and secondary mirror can be fabricated and mounted using the same techniques, affording less stringent global profile requirements during fabrication. The components are literally bent into final shape with minimal high spatial residual error in the telescope, making the system function at optimum

The first two mirrors for the Advanced X-Ray Astrophysics Facility have been successfully fabricated and tested. The methodology developed has demonstrated figure convergence rates previously unseen on large area, precision optics. These results were based on developing a unified systems approach to fabrication and testing aided by the extensive use of analytical models. This paper presents a summary of the optic requirements, an overview of the fabrication process, the metrology used, and a summary of the results

Silicon carbide (SiC) has become a legitimate competitor to beryllium (Be) for large lightweight mirrors due to its high stiffness to weight ratio and low thermal expansion. However, there are many kinds of SiC and some are better suited for mirrors than others. After a comparison of the various SiC types we described one type of reaction bonded SiC that can be near-net-shape fabricated into very lightweight mirrors in sizes ranging from a few centimeters to greater than two meters. Lightweight spherical mirrors of 0.18 and 0.50 m diameter have been fabricated and polished to very low surface roughness. The blank and optical fabrication techniques are described, and characterization data are presented for uncoated polished surfaces. These mirrors have surface roughness of 8 - 15 angstroms rms and (lambda) /10 figure

A program to fabricate a large, optically fast, aspheric lightweight Be mirror was initiated in order to demonstrate state-of-the-art technology. The mirror blank was fabricated as a 1.0 m diameter, f/0.58 ellipse directly from IP-70 grade powder using near-net-shape hot isostatic pressing (HIPing) and a patented tooling approach that produced a closed back, honeycomb- cored mirror weighing less than 18 kg. Details of the mirror design and of the assembly for HIPing are given. The blank was HIPed, leached, and machined to final shape with all design goals met. The as-HIPed blank was within +/- 0.5 mm in all dimensions and the radius of curvature was within 0.2 of target. The mirror was loose-abrasive ground using plunge grinding with a full-size tool, then polished using a full-size flexible pitch lap. In-process metrology utilized a special-purpose swing-arm profilometer with demonstrated accuracy and repeatability of

Optical system designers in the 1990s will require many unique solutions to the issues involved in high quality ground-based and space-based optical systems. To meet the scientific needs of the future, many optical systems will require large apertures which can use segmented, ultralightweight elements. Eastman Kodak Company has developed a number of manufacturing processes for ultralightweight, off-axis optical elements. These processes include mirror core fabrication with an abrasive water-jet system, computer-controlled contour surface grinding, computer-controlled small tool grinding and polishing, and ion beam surface figuring. To allow the engineered design of mirror blanks, a computer-controlled abrasive water-jet system is being used to fabricate ultralightweight mirror cores economically. This paper reviews some techniques for mirror substrate fabrication and lightweighting, including an approach being developed at the Eastman Kodak Company using a computer-controlled abrasive water-jet system

This paper describes optical testing procedures used at the National Optical Astronomy Observatories (NOAO) for testing large optics. It begins with a discussion of the philosophy behind the testing approach and then describes a number of different testing methods used at NOAO, including the wire test, full-aperture and sub-aperture Hartmann testing, and scatterplate interferometry. Specific innovations that enhance the testing capabilities are mentioned. NOAO data reduction software is described. Examples are given of specific output formats that are useful to the optician, using illustrations taken from recent testing of a 3.5- meter, f/1.75 borosilicate honeycomb mirror. Finally, we discuss some of the optical testing challenges posed by the large optics for the Gemini 8-meter Telescopes Project

Interferometry is not adequate for surface measurement of large mirrors during the early stages of figuring. Edges tend to roll off with errors of many waves, and these errors are undetectable with interferometry. The Hartmann test has become very important in providing surface information during these early stages, but unfortunately, data reduction is quite slow. Itek now has an instrument to automate the Hartmann test using a scanning laser beam and a solid state sensor. A narrow laser beam scans the testpiece in an appropriate raster. A solid state detector senses the reflected spot in the vicinity of the center of curvature. Knowing the positioning of the beam, and the position of the reflected spot is sufficient information for a mirror slope determination of that raster position. A computer program integrates the slope data to produce a surface wavemap of the testpiece. This wavemap can be displayed on a contour plot within a few minutes or routed to a computer controlled Milacron robot to appropriately refigure the testpiece. A null lens is unnecessary. The measurement accuracy of the instrument is about 1/5 to 1/2 waves surface rms

A ten meter astronomical telescope is being constructed using a phased array of two meter segments. This requires manufacture of a large number of off-axis segments and emphasizes the desirability of rapid manufacture and smoothness of finish of the segments. These two requirements have been met at Itek by combining surface figure measurement of a mirror using a multiple probe mechanical bar profilometer and fabrication of that mirror by stressed mirror polishing. Through the use of the multiple probe bar profilometer, a mirror segment can be measured to an accuracy of 0.047 microns rms surface error in a period of less than 90 minutes, including data processing time. This test has allowed us to manufacture 12 off-axis segments with a final surface error, after low-order correction by the in-use mount, of approximately .02 microns rms. The average rate for the entire grind and polish fabrication cycle is six weeks per mirror

In this paper we have used the method of finite element analysis to study some candidate composite materials - carbon fiber reinforced epoxy and glass fiber reinforced epoxy. These composites may have real applications in the design of the optical support structures of very large telescopes where stringent thermomechanical stability are much needed. The lightweight property of these materials allow one to build very stiff members for the optical support to withstand the structural deflections due to wind vibration and gravity. We have run finite element models of these composites using ABAQUS on a VAX VMS computer. Simple beams with rectangular crosssections were computed for the composites with structural steel as a comparison. The static properties of these beams were studied.

This work is a new approach for the design of start optical systems and represents a new contribution of artificial intelligence techniques in the optical design field. A Knowledge-Based Optical-Systems Design (KBOSD) based on artificial intelligence algorithms first order logic knowledge representation rules and heuristics on lens design is realized. This KBOSD is equipped with optical knowledge in the domain of centered dioptrical optical systems used at low aperture and small field angles. This KBOSD generates centered dioptrical on-axis and low-aperture optical-systems which are used as start systems for the subsequent optimization by existing lens design programs. This KBOSD produces monochromatic or polychromatic optical systems such as singlet lens doublet lens triplet lens reversed singlet lens reversed doublet lens reversed triplet lens and telescopes. In the design of optical systems the KBOSD takes into account many user constraints such as cost resistance of the optical material (glass) to chemical thermal and mechanical effects as well as the optical quality such as minimal aberrations and chromatic aberrations corrections. This KBOSD is developed in the programming language Prolog and has knowledge on optical design principles and optical properties it is made up of more than 3000 clauses. Inference engine and interconnections in the cognitive world of optical systems are described. This KBOSD uses neither a lens library nor a lens data base it is completely based on optical design knowledge.