Until now, the development of an Electro-Optics Manufacturing Technology Plan has been primarily passive. That is, specific projects were selected from submitted Manufacturing Technology Proposal Briefs, (NAVMAT Form 4800/2) on the merits of each individual project. While some valuable projects came about as a result of this procedure, such an approach does not necessarily identify and address the most critical Navy needs in the area of Electro-Optics manufacturing. This paper has been prepared to: Disseminate to the Navy E-0 community, information on all E-0 MT projects, either fund-ed or submitted for funding. Solicit comments on and prioritization for these existing E-0 MT projects. Solicit additional E-0 MT projects or other valuable information (via a simple form).
The Antares CO2 laser system is being constructed at the Los Alamos Scientific Laboratory (LASL) to investigate inertial confinement fusion. Antares will be a very large laser system, with 72 beams and a total beam area of some 6 square meters. There will be thousands of optical components, predominantly copper-plated mirrors and sodium chloride windows. To coordinate the specification, procurement, evaluation, and disposition of these components, a centralized Optical Evaluation Laboratory (OEL) is being set up. The OEL is principally a quality-control facility for routinely evaluating the optical performance of components and assemblies with apertures of up to 18-inch diameter. However, the OEL has a much broader involvement and responsibility for the Antares optics. Virtually every piece of optics in Antares will be specified and ordered through the OEL. After acceptance, the OEL will be responsible for tracking the history of each optical com-ponent via a computerized data base. This paper describes the Optical Evaluation Laboratory facility and its operation.
Techniques for assessing the performance of optical components for infrared high energy laser systems are described. The techniques include photometry and interferometry of large aperture components, diffraction grating efficiency measurements, absorption calorimetry, and reflectometry. A brief summary of the methodology of each type of measurement is presented.
This paper describes an automatic pattern processor which can be utilized for reducing both simple and complex interference patterns derived from high quality optical surfaces. The complex patterns may be produced either by optical interference phenomena or by contour patterns obtained from either holographic or Moire techniques. The rapid, accurate measurement and analysis of even simple interference patterns has heretofore been tedious and time consuming due to the unavailability of objective, affordable instrumentation. In practice, many interference patterns can have poor contrast, such as in some Moire or holographic tests; large fringe deviations, such as in aspheric testing; and high spatial frequency deviations, as with diamond turned surfaces. For these cases, the measurement problems become significantly more formidable.
Two high-speed, multi-actuator deformable mirrors have been characterized in terms of their abilities to provide low order Zernike mode shapes. Both mirrors are piezoelectrically activated with one having 61 actuators in a concentric circular array and the other having 52 actuators in a cornertruncated square array. Tilt, focus and astigmatism modes have been imposed with good linearity and fidelity. Superposition of multiple modes has also been successfully demonstrated. Problems encountered are listed.
A method has been developed for evaluating interferograms using portable, inexpensive equipment. The method involves least square fitting the Zernike polynomials to interferogram data. An interferogram Can be data reduced typically within 15 minutes, yielding information about the optical aberrations present.
Mirrors are tested at the Thermal Distortion Test Facility (TDTF), Kirtland AFB, Albuquerque, NM, using a rastered electron beam (E-beam) to thermally load the mirrors. Typical test results and their implications are presented. The capabilities and accuracies of the facility are discussed. Verification tests performed with a CO2 laser confirm the validity of using a rastered E-beam to simulate a HEL beam thermal loading.
The use of axicons and related types of optical components is of increasing importance in high energy laser systems. To aid in the acceptance testing of these optics, a program for the development of diagnostic tools and techniques for axicon evaluation has been undertaken by the Developmental Optics Facility at the Air Force Weapons Laboratory. Analytical models describing both the wavefronts and far-field patterns of systems containing axicons have been developed. These models have been used to derive methods for testing axicons in the laboratory. They have also been used to develop suggestions for the initial parameter specifications of axicons. Finally, methods for the correction of certain types of axicon aberrations due to fabrication errors are discussed.
Techniques for evaluating the diffraction efficiency of infrared gratings have been developed and utilized at the Air Force Weapons Laboratory as part of the high energy laser component development effort. The key to accurate infrared diffraction efficiency measure-ments is good angular alignment and linear detection. The AFWL OMiGA diffraction code has proven to be very useful in determining the expected efficiencies of various coated and uncoated grating designs. Successful use of this program requires a good method of determining the groove profile of the grating. One successful method that we have developed will be discussed.
Axicon elements are used in cylindrical optical systems such as high-power chemical lasers. Interferometric tests of such elements cannot be interpreted by standard methods. Axicon aberrations of cone error and decenter error are defined to help interpret such interferograms. A preprocessing option was added to FRINGE to treat axicon data. An example interferogram has been analyzed.
In the fabrication of fast aspheric mirrors having diameters in the 20-30 inch range, it ceases to be practical to introduce the required correction by polishing alone. One is faced, therefore, with aspheric figure control of a surface which cannot be tested optically. To overcome this problem we have adopted the use of precision profile monitors which can provide a prepolishing surface having an accuracy of better than one micron. Upon reaching the polished stage we have found that a wire tester provides the most convenient means for figure control. However, for the final stages of polishing, where local hand correction may be required, it is desirable that the wire tester be replaced by a full aperture interferometric technique; usually a null lens. Described in this paper is a three stage monitoring procedure which uses a profile monitor, a wire tester and a null lens. Accuracy and convenience of each technique are discussed. Also, suggestions are made concerning the optimum point at which one instrument should be exchanged for another.
The angular distribution of light scattered from optical surfaces is best described by a Bidirectional Reflectance Distribution Function (BRDF). Scattered light in spaceborne optical systems may be induced by surface contaminants that are present only under the combined conditions of extreme cold, high vacuum, and strong ultraviolet radiation. An instrument is described that gqnerates surface contaminants and measures BRDF in situ. Measurements are performed at 10-0 Tarr pressure and at 77K for angular scatter ranging from one degree away from the specular reflected beam to sixty degrees away from the specular reflected beam. Measured BRDF intensity ranges from 10-° watt per incident watt per steradian to 10-6 watt per incident watt per steradian.
A surface contour measuring machine is described which can measure general aspheric or axi-symmetric aspheric surfaces repeatably to .000005 inches or better in most cases. The computer system which controls the measuring machine and which performs the data analysis is discussed. Aspheric production applications are shown in which the measuring machine plays a vital role.
A unique and versatile laser interferometer has been jointly developed by Honeywell, Tropel and the University of Arizona. The system is designed for routine non-contact testing of aspheric optical surfaces (using a Computer-Generated Hologram [CGH] to provide the aspheric component of the reference wavefront) while retaining the features and capabilities of the standard Tropel Vertical Interferometer. Thus it is capable of measuring radius and/or optical figure of spheres, flats, conics and general aspherics. The instrument provides convenient interchangeability among Fizeau, Twyman-Green, CGH and Lateral Shearing modes of operation in a single compact unit. It is also capable of direct inter-facing with a computer for wavefront measurement or analysis. The operation of the system is described and data is presented from a CGH test of an f/2 paraboloid (using a spherical test wavefront) for which independent comparative data is also given.
Small grinding and polishing tools are useful for certain applications since they can closely follow the curve of an aspheric surface and are less affected by workpiece distortion than larger tools. Also, the use of a computer to control the action of grinding and polishing tools can increase the efficiency and accuracy of the process. The computer controlled polisher (CCP) takes advantage of both features, moving a tool assembly with small pads over the workpiece under computer control. By varying the amount of time the machine works any region, a controlled amount of material may be removed. Using computer modeling, the best tool configurations are developed to perform any figuring operation. Based upon experimentation, the proper operating parameters for the CCP have been obtained. The machine has been used to fabricate a number of difficult mirrors. As a result of this work, the CCP will be used on important fabrication efforts.
A simple method is described which permits the rapid fabrication of nickel plated aspheric metal mirrors for infrared optical systems. The method employs precision machining of the substrate and the plated mirror with a calculated series of tangent radii designed to closely approximate the desired aspheric curve. The process described has several advantages; it removes irregularities from the substrate and the plating, it provides an even plating layer, it produces a smooth machined surface close to the desired shape and ready for polishing and figuring, and it can be done on most precision machine lathes. Since most of the asphericity is machined into the surface at the start, a considerable reduction in fabrication time can be realized over conventional methods.
A development program involving the design, fabrication and testing of low-efficiency, low-absorption grating beam samplers is described. Two different basic designs were selected for development. The first design is a low-efficiency grating with a high reflectivity multi-layer dielectric coating. The second design is a "buried grating", which consists of a blazed grating under a ZnSe spacer layer, with a high reflectivity multilayer overcoat. The fabrication problems associated with each type of beam sampler are discussed. The comparison of experimentally measured absorptivity and efficiency with values obtained from computer cal-culations are presented. An additional effort currently underway to make very low absorptivity beam samplers by generating periodic refractive index variations in the dielectric stack is also discussed.
Antares is a large carbon-dioxide laser system presently under construction at the Los Alamos Scientific Laboratory (LASL). Antares will be part of the LASL High Energy Gas La-ser Facility (HEGLF). Its purpose will be to investigate inertial confinement fusion with light of 10.6-μm wavelength: Most of the optics comprising Antares will be reflectors and, for many reasons, copper is the material of choice. The mirrors range in size from 2.5 cm in diameter to 45 cm in diameter. The copper must be very pure to help maximize damage threshold, making plated copper an attractive solution. The final mirror should be very stable, i.e., characterized by very low microcreep. This makes an alloy a more suitable substrate candidate than pure copper. For Antares, all of the smaller mirrors will be made of copper plated onto an aluminum-bronze substrate, and all of the larger mirrors will be made of copper plated on-to aluminum alloy 2124. This paper discusses how this design was arrived at and the methods used to assure a satisfactory mirror.
Typical mirrors used in high power gas laser applications are of molybdenum construction and employ thin faceplates which overlay a multitude of narrow gauge cooling channels. Since such mirrors are extremely costly, it is desirable that they be refurbished rather than replaced when their surfaces are burned by laser radiation. However, the faceplates are quite thin (0.010 - 0.020 inch); allowing only a limited number of refurbishments by straightforward grinding and polishing techniques. To overcome this lifetime restriction, we have adopted a refurbishment procedure which employs the sputtering of pure molybdenum upon the damaged surface prior to grinding. In this manner it has become possible to resurface mirrors without reduction in structural integrity. Described are details of the techniques currently employed together with the precautions necessary for the production of defect free sputtered coatings.
Nonlinear holographic gratings developed for high energy laser systems have led to new possibilities in large, lightweight primary mirror designs. The beam sampling technique has made the concept of local loop adaptive optics correction much more attractive because all optical distortions including those in the primary mirror can be corrected.
A dichroic (or multichroic) beam splitter operating in the high energy laser HEL environment is called a shared aperture component and is becoming an increasingly desirable component in the design of HEL systems. At present, there are four basic types: Buried Short Period (BSP) grating, Buried Long Period (BLP) grating, Dichroic Beam Splitter (DBS) and Compound Interlaced (CI) grating. The BLP grating and CI grating are new types of grating which have recently been proposed and are currently under development. This paper describes the four basic types and their characteristics. Their design and fabrication issues and present technology status are also discussed.
The production technique used for high homogeneity, fluorophosphate laser glass is reviewed. Different types of inhomogeneities are discussed and methods of prevention are given. An experiment on the effect of annealing on homogeneity is investigated.