In this issue, we present a series of papers addressing, in a variety of ways, the general subject of optomechanical design. That this is an interdisciplinary subject has long been recognized by many of those scientists, designers, and engineers engaged in the evolution of optical instruments. Indeed, Donald H. Jacobs voiced his conviction on this matter way back in 1943 with the words, "In the design of any optical instrument, optical and mechanical considerations are not separate entities to be dealt with by different individuals but are merely two phases of a single problem."1
Optical systems often have to operate over a wide temperature range. The effects of temperature changes on the performance of some typical optical systems are described in this paper. Methods used to counteract such variations in optical properties range from servo-controlled motion of the components and bimetal mounts with reciprocating motions to, as this paper describes, a simple choice of appropriate optical and mount materials. The optical systems considered range from single lenses to high quality multielement imaging systems.
A 36-inch f/5.0 lens and a 24-inch f/3.5 lens used for aerial reconnaissance missions are described. During design, these lenses were analyzed over t heir full operating temperautre range of 20 to 60 C. Their performance at ambient conditions and at the maximum operating temperature is reported. The results indicate that at steady state the performance of each lens is affeted only modestly over the operating temperature range when the image is held in focus by a thermal comensating lens mount.
Predicting performance of electro-optical systems that operate while being subjected to thermal/mechanical loadings has been accomplished by integrating computer-based numerical tools. Honeywell has interfaced thermal, structural, and optical computer programs on both CDC 6600 and Honeywell 6080 computers into a Thermal/Structural/ Optical (TSO) evaluation process. The TSO process integrates the separate analyses by automatizing data transfers among the individual technology programs to permit rapid evaluation of optical systems undergoing thermal/mechanical loadings. The design/analysis process involves iterating the following: thermal/ mechanical error budgets, TSO evaluations of electro-optical systems, and comparisons of TSO results with error budget line items. This paper presents how the TSO process has interfaced the individual technology programs, examples of TSO applications to Honeywell electro-optics systems, and test data from systems that have been subjected to thermal/mechanical loadings. The thermal/mechanical loadings include cryogenic loads, steady state acceleration, random vibration, and decaying dynamic loads. The examples show how the process has been effectively used during the design/analysis stages of projects to evaluate alternate design concepts. The resulting process has resulted in a cost-effective methodology for predicting performance of electro-optical systems undergoing theral/mechanical loadings.
Tolerancing plans range in complexity from those in which all parameters are investigated, documented, and controlled, to those that rely solely on whatever quality of optics, mechanical parts, and assemblies is present. The level of complexity desired depends not only on technical considerations but also on cost, schedule, etc. An outline is presented which is applicable not only to the more complex tolerancing plans but also to more modest efforts. The various activities and documents of the complete tolerancing plan are described and illustrated with a view toward clarifying their functions. The outline together with the activities and documents should provide a point of departure for establishing an effective tolerancing plan in a given situation.
It is the task of an optomechanical engineer, starting with a lens design provided by the optical designer, to devise a structure which holds various components of a lens in proper axial and radial alignment. This structure, the lens barrel, must provide a means of interfacing with the customer's system, and must be designed so as to maintain optical and mechanical integrity under a multitude of environmental conditions. This discussion encompasses the design and analysis efforts undertaken by the optomechanical engineer to comply with this requirement. Additionally, some special areas of concern to the optomechanical engineer such as various centration and assembly techniques, cementing of optical components, sealing and leak rate analyses, and reliability estimates of lens assemblies are discussed.
The ability to produce strain free mounts for metal mirrors is shown to be feasible by the application of four principles: - Mounting strain isolated from mirror surface - Mirror stiffer than mount - Mirror figured in "as mounted" strain condition - Mount tolerances equal to surface tolerances The application of precision diamond machining is shown to be advantageous in applying these principles. Several real mirrors are shown as examples.
Abstract. The design of an operational mount to rigidly secure the primary mirror to its baseplate without the introduction of figure error always proves to be a major task on diffraction limited optical systems. A summary of the design of the Infrared Astronomical Satellite (RAS) primary mirror mount is given. The mirror was designed to be aligned and tested at room temperature and operated in a zero "g"field at temperatures of 2 Kbo minimize overstressing, a stiffness requirement of greater than 150 Hz was required for cold launch and room temperature vibration acceptance testing. Additional isolation was required to minimize strains, introduced via the mounting base, due to thermal and mechanical distortions.
Room temperature alignment and evaluation techniques for the Infrared Astronomical Satellite (IRAS) telescope which has a primary mirror figured to correct for surface distortions at the 2 K operating temperature will be discussed. Interferometric cryogenic testing of the 0.6 meter, f/1 .5 light-weighted beryllium primary mirror at its intended operating temperature revealed surface distortions that could be modeled with Zernike polynomials. With this model, it was possible to derive the -inverse- of the cryo wavefront error (ideal cryo mirror) and figure the cryo correction into the primary mirror using Perkin-Elmer's Computer Controlled Polisher. It was recognized that during room temperature assembly of the system, misalignment of the secondary mirror could introduce additional unwanted aberrations that would cancel or distort the wavefront errors purposely intro-duced by the cryo figuring. To avoid this possible degradation and to ensure optimum telescope performance, the system Zernike polynomial coefficients and wavefront maps generated from the in-process alignment interferograms were monitored and compared to Zernike coefficients and wavefront maps for the cryo corrected primary mirror. Using Zernike polynomials to monitor the optical quality of the telescope enabled figure and alignment errrors to be monitored, and demonstrated that the alignment tolerance was achieved.
The U. S. Army's new M1 9 binocular, which incorporates an unusual modular assembly concept for simplified maintainability, is currently being produced at the rate of 2,000 per month. In succeeding sections of this paper, the origin and development by the Army of the modular concept for this binocular are reviewed briefly and performance requirements are summarized. Following this, the manufacturing engineering approach and implementation developed and carried out by the Optical Division of Bell & Howell Company in producing the M19 binocular are presented.
Historical background is presented of the U. S. Army's requirement for a high performance, lightweight, night vision goggle for use by helicopter pilots. System requirements are outlined and a current program for development of a third generation image intensification device is described. Primary emphasis is on the use of lightweight, precision molded, aspheric plastic optical elements and molded plastic mechanical components. System concept, design, and manufacturing considerations are presented.
"Ebsicon" is the generic name for any camera tube which contains a photoelectron-bombarded silicon diode array target. Following a description of the motivation for and the development of a large-format ebsicon (one containing an 80 mm photocathode and a 32 mm silicon target), the features of the device are presented. Emphasis is placed on the point-source performance of the tube in terms of the achieved point-source image cell density and the point-source response fall-off away from the center of the scanned area. Photocathode requirements are discussed in the context of the expected per-formance of the Air Force's upcoming Ground-based Electro-Optical Deep Space Surveillance (GEODSS) system. Then, field measurements for exposure times of 0.6 and 1/30 second, using G-type stars, are described and compared to the projected performance of a GEODSS electro-optical sensor. Finally, a list is presented of additional, important, and measured features of delivered, large-format ebsicons.
A versatile optical instrument capable of all-sky auroral imaging at low light levels is described. The All-Sky Imaging Photometer uses as a detector an image dissector photomultiplier tube operating in a photon-counting mode. A miniprocessor interprets commands entered interactively by the operator through a terminal, and controls data acquisition and display. A motorized filter wheel holding up to six interference filters permits monitoring of auroral emis-sions at monochromatic wavelengths.
Refractive index changes in all types of optical media induced by an optical field through resonant and nonresonant mechanisms with submicrosecond responses are surveyed in this paper. Relevant data for over 100 representative media have been compiled and tabulated, and numerical examples have been worked out for several important media. For room-temperature operation, solid polydiacetylenes, CS2 liquid, and N2-buffered 12 vapor are found to be roughly comparable in sensitivity for self-induced phase shift for a given transmission loss. Nitroaniline compounds are somewhat less sensitive but also interesting. For operation in the 10 µm region, n-InSb is most sensitive. If operation at somewhat elevated temperature (100 to 200 C) is acceptable, then N2-buffered alkali-metal vapors are the best with about two orders of magnitude higher sensitivity. At liquid nitrogen temperature, a thin film of CdS could be as sensitive as a 105 times thicker sample of PTS polydiacetylene if the signal frequency is near the intrinsic exciton lines of CdS.
A transmission holographic microscope is described. The technique consists of using a suitable holographic beamsplitter associated with the condenser of the microscope. An imaging system ensuring optical paths of equal length from the beamsplitter to the recording plane allows the use of this technique in nonmonochromatic light (spectral or arc lamps).
The production of cylindrical holographic stereograms, or multiplex holograms, requires the use of a large, low f/number cylindrical lens to form a line image on the holographic film. To have an image of reasonable size for display purposes, the f/number of the lens must be quite small, on the order of f/1, and the dimensions of the lens must be reasonably large, on the order of eight inches in width and height. The optical quality of the lens must also be quite good to prevent interference fringes in the image and to minimize the number of multiple exposures in the multiplexing process. For economic rea-sons, adjustable, oil-filled plastic lenses are commonly used for this purpose instead of conventional optics. Considerable difficulty is usually encountered, however, in adjusting the oil lens to minimize aberrations. Making the oil lens adequately adjustable, while at the same time maintaining the oil seal, also presents mechanical difficUlties. We have eliminated these problems with the use of an off-axis, holographic cylindrical lens. The lens is easy to make, requires no adjustment, and has excellent optical quality. Techniques for producing this lens and its use in making multiplex holograms are described.
The image width in cylindrical holographic stereograms has been limited to about one-third the diameter of the display drum. An analysis of the optical system shows that producing an image which fills two-thirds of the drum diameter or more requires a cylindrical lens with an f/number of 0.5 or smaller. Cylindrical lenses of such small f/number and adequate optical quality are not commonly available. These optical characteristics can be achieved readily, however, with a holographic element on a curved surface. A system designed for increasing image width making use of such a holographic lens is described. The requirement for an extremely low f/number cylindrical lens can be eliminated by another technique which involves curving the holographic film over a short radius platen. This technique is also described. It is shown that both these techniques compensate the nonlinear horizontal magnification distortion in cylindrical holographic stereograms.
A method for automatically measuring the three-dimensional (3-D) deformations of a diffuse surface is studied, using a real-time holographic interferometer and a television-computer system. The object surface is illuminated from three different directions. The scattered waves are recorded on a thermoplastic hologram. Real-time holographic interference patterns are observed through the hologram in a fixed direction by sequentially applying the three illuminating beams. The three fringe patterns are put into the computer using a television (TV) camera. The relative fringe order numbers are determined over the whole surface. Calculations for obtaining 3-D deformation distributions are performed, and the results are displayed on a cathode-ray tube (CRT) monitor.
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.
Optics has had a significant impact in the development and implementation of medical acoustical imaging. Principles of optical systems theory and optic instrumentation have played an important role in the conception, design, and development in new ultrasonics research tools for diagnostic imaging and tissue characterization; this is ex-emplified in the paper with a few acoustic imaging systems. A potential imaging system whose success relies on the interface between the optical subsystem and the acoustic subsystem is described. This system would have the advantage of operational flexibility and electronic simplicity. The present obstacles and possible solutions are discussed.
Temperature distributions and species densities can be determined in cylindrical plasmas by using the Abel inversion technique to obtain the volumetric emission coefficient from lateral radiance measurements on optically thin spectral lines. These diagnostics are especially useful for studying arcs and glow discharges. Extensive spectroscopic measurements and data analysis routines are required for each determination, and user-interactive judgments are required at several points in the analysis. We have interfaced a Polymorphic 8813 microprocessor-based computer with our spectroscopic instruments for this task. The computer speaks BASIC and has 56 kbytes of user-available RAM. An S-100 compatible analog interface board is used for control of an optical spectrometer and a translation stage, as well as for digitization of the data in real time. Software was written for filing the data on mini-floppy disks, performing data analysis, and printing or plotting the results with a small line printer or with an X-Y recorder. We were able to obtain a reliable and productive facility without large capital equipment outlays because of the modest cost of the microprocessor-based computer and its ability to interact with the expensive equipment that was already on hand.
A new modified bootstrap approach to sensitometry is presented which provides H and D curves that show almost exact agreement with those obtained using conventional methods. Two bootstrap techniques are described; both involve a combination of inverse-square and stepped-wedge modulation of the radiation field and provide intensity-scale sensitometric curves as appropriate for medical radiography. H and D curves obtained with these modified techniques are compared with those obtained for screen-film combinations using inverse-square sensitometry as well as with those obtained for direct x-ray film using time-scale sensitometry. The stepped wedge of the Wisconsin X-Ray Test Cassette was used in the bootstrap approach since it provides sufficient exposure latitude to encompass the useful density range of medical x-ray film. This approach makes radiographic sensitometry quick and convenient, allowing accurate characteristic curves to be obtained for any screen-film cassette using standard diagnostic x-ray equipment.
The application of the Kolmogorov-Smirnov, non-parametric statistical tests to image processing is presented. Examples are shown for image segmentation and target detection in a series of thermal infrared (8 to 14m) images. Advantages of real-time operation are discussed.
Frequently an image may be blurred by a point spread function whose details are not known exactly. In such a case, it is necessary to estimate the point spread function before deconvolving the blurred image. This paper presents a new technique for estimating a zero phase blurring function when its optical transfer function is smooth. The estimate is obtained by smoothing the spectral magnitude of the image and comparing it to an average magnitude that is also smoothed. The average magnitude is obtained by averaging over an ensemble of similar images. The estimate can be extended to degradations such as a defocused lens by thresholding the estimation magnitude to obtain zero crossings and adjusting the phase accordingly. In particular, this technique can be applied to a circularly symmetric Gaussian blur or a defocused lens with a circular aperture.
A helium-cooled telescope of 15 cm aperture is being designed and constructed jointly by the University of Arizona, the Smithsonian Astrophysical Observatory, and the Marshall Space Flight Center for high sensitivity infrared astronomical observations from Spacelab 2. A focal plane array of ten detectors provides a total field of view of 3° and covers the wavelength regions 4.5-8.5 um, 6-7 um, 9-16 um, 18-30 Am, and 60-120 um. A highly redundant all-sky survey will be conducted by repeated scanning of the sky during many orbits of the spacecraft. High redundancy will allow discrimination among variable and constant celestial sources and several types of variable nearby sources. The principal astronomical result of the survey will be the absolute flux measurement of low surface brightness, large scale celestial infrared (IR) emissions, but it will also extend existing IR sky surveys by a factor of 10 in point-source sensitivity. The experiment will also make significant engineering measurements of contaminants in the Shuttle environment, test the technology of storage and utilization of large quantities of superfluid helium in space, demonstrate techniques for sensitive infrared measurements from space, and test mechanical designs for future infrared telescopes for the Space Shuttle.
An instrument to measure inhomogeneity of optical materials in the 3 to 5 um as well as in the 8 to 12 pm region is described. It measures the deviation caused by inhomogeneous areas when a light beam passes through. A line spread function is formed with an auxiliary lens, and in its slope a fixed measurement slit is positioned. Deviation caused by inhomogeneities will shift the spread function, and the measurement slit will detect variations in intensity. With this technique the gradient of the refractive index, as well as the variation of the refractive index, can be measured. Typical measurement results are shown.
The Advanced X-ray Astrophysics Facility (AXAF) is to be a free-flying national x-ray observatory that is Shuttle-launched (in mid-1988), maintainable on-orbit, and retrievable. The design lifetime is > 10 years. The AXAF is conceived as an x-ray telescope with 6 nested Wolter type I mirrors (maximum aperture of 1.2 m), a focal length of 10 m, and interchangeable and replaceable focal plane instruments. The optics will provide 0.5 arcsecond imagery over a several arcminute field and somewhat reduced resolution over 1 degree in the x-ray band from 0.1 to 8 keV. The performance requirements and design of the facility will be discussed and comparisons made with an existing x-ray observatory. The scientific objectives of the AXAF will also be discussed briefly.
A new method for dynamically deforming a thin mirror to correct the phase aberration function for defocus and astigmatism is presented. Three piezoelectric-type actuators, attached to the back edges and parallel to the front surface of the mirror, induce edge moments that bend the mirror to its desired shape for correction of the aberrated wavefront. A three-actuator deformable water-cooled mirror breadboard has been designed and built. Major features, design constraints, and performance expectations of the deformable mirror design are described.
A discrete actuator deformable surface device, which provides as much as 12 pm of surface deformation using ±1 kV, has been developed at Itek. The discrete actuator device, made from bonded layers of piezoelectric discs, has been continuously exercised for a period of several hundred hours. No change in surface figure was observed even using a dilatation level of 6 microns. By employing both optical and electrical techniques, the fundamental mechanical resonance has been measured and found to depend upon the boundary condition in a complicated manner.
The laser speckle velocimeter based on the zero-crossing rate of the spatially integrated speckle intensity variations is studied under various optical configurations of illumination and detection. The eliminating method of the additional noise is also experimentally investigated by using Schmitt trigger circuits for the counting of zero-crossings.
A simple CO2 laser can be caused to exhibit a specific sequence of five rotational lines or "colors" with cavity length tuning. The sequence, useful in multicolor interferometric distance measurement, is predicted to appear only near certain discrete laser cavity lengths. Three different length breadboard lasers are described in which a desired sequence is found.
In keeping with my desire to make editorial decisions openly and to seek reader response to those decisions, I want to announce a policy on the citation of military classified information in Optical Engineering. The problem, is a vexing one. If the purpose of a paper is to convey the maximum amount of information about a topic, should it trouble your editor that otherwise-useful references are inaccessible to some of the readers? Should he deliber-ately suppress the information that related material is available because some of the readers cannot use that material? Should the editor ban references to an obscure Dutch journal (for example) because some of the readers cannot use that material? Yet, there is something distasteful about citing classified material. Does it make Optical Engineering American and not international? Could it become a Department of Defense outlet for unclassified information? Would it be elitist?
The program presented here is written for the Texas Instruments TI-59 calculator with PC-100 printer. It provides a means for evaluating the third-order surface contributions to the aberrations of an optical system. The program can handle a system of up to 16 surfaces, and up to two of these can be aspheric.