This paper describes the development of an infrared tunable acousto-optic filter. A Te02 noncollinear filter was designed, constructed and tested for operation in the range of 2.5 to 5.5 micrometers. The filter has a measured spectral resolution of 16 cm-1 at a f/2.5 aperture. Application of the filter to optical coherence detection in the infrared is described.
In an ideal infrared optical system, all available energy in the wavelength region of interest would be transmitted to the detector. But, every surface in an optical system distributes incident energy into reflected, transmitted and absorbed portions. The usefulness of interference coatings is based on their potential for altering the properties of surfaces to provide optimum use of available energy. Interference coatings are discussed here with respect to their influence on energy distribution at surfaces. The discussion will include coatings for reflecting and transmitting components, as well as filters and beamsplitters. Theoretical data and measured performance are used to show how well available coatings utilize the energy incident on them.
A modified Ebert-Fastie spectrometer has been designed for use as an atmospheric temperature sounder. It uses a fixed grating, and the first four orders are imaged onto a set of rigidly mounted detectors. Some fundamental properties of the design are reviewed, and some interesting imaging properties are discussed.
Historically, FLIRs have usually utilized single-FOV or dual-FOV optical systems. The advantages of using a zoom optical system and thereby continuously varying the FOV coverage or scene magnification are numerous. Until recently, however, infrared zoom optical systems were considered to be impractical and incapable of providing acceptable image quality unless an excessive number of optical elements were used. A mechanically compensated, parallel-scan, 5:1 continuous zoom FLIR optical system has now been designed, debugged in the prototype stage, and is in production. Although the optical design was severely restricted by the packaging requirements, only six refractive elements are used, a number that is sufficient to ensure almost diffraction-limited image quality, especially toward the shorter focal lengths of the zoom range. Since two lens surfaces are convex paraboloids, special problems had to be solved to allow manufacture in production quantities. Thermal compensation, especially in the presence of temperature transients and gradients, was effected by using an analog computer to control the motion of one lens element in order to maintain focus.
There are three major computer programs for optical design and analysis which are available to anyone through purchase, lease, or royalty usage arrangements. These programs are ACCOS V from Scientific Calculations, Inc., the David Grey programs available through Genesee Computer Center, Inc., and CODE V from Optical Research Associates. This paper will discuss the relative merits of each of these three programs in dealing with the various types of specialized problems involved in the design of FLIR type optical systems. These problems are specialized in the sense of being different from those normally encountered in the design of visual optical systems, and include spectral range characteristics, multimode (including zoom) designs, scanning systems, and vignetting and narcissus considerations. Examples of these various problems will be presented.
A technique is described for use in determining the effect of opto-mechanical tolerances on the radiometric performance of a typical laser rangefinder system consisting of a laser, transmitter, and receiver. This technique takes into account centered tolerances, laser performance parameters, and the alignment boresight to the subsystems. These subsystems are perturbed within selected tolerance limits by means of the Monte Carlo method, and the individual perturbed subsystems form a simulated system. The simulated system is then analyzed to determine its radiometric efficiency. A histogram based on the number of systems simulated is prepared that illustrates the probability of radiometric efficiency. This distribution varies with the tolerances selected, laser performance parameters, boresight errors, receiver FOV, etc. The technique described is an excellent engineering tool for analyzing and specifying subsystem performance parameters.
The use of aspheric elements in FLIR type infrared systems is shown to result in system performance improvement. Improved image quality, reduced shading and higher transmission can be obtained, while at the same time, reducing the system cost. The manufacturing and test technologies which allow for cost effective use of aspherics are described. An advanced small FLIR which uses aspherics is cited as an example of the concepts presented.
Thermal electro-optical imaging systems require windows fabricated from materials that are not only transparent to infrared radiation but also possess adequate structural strength to successfully withstand loads imposed on them by operational scenarios. Optical grade mono-and polycrystalline germanium has found wide acceptance for applications in the 8 to 12 micron wavelength region where the windows are exposed to high pressure in the presence of moisture, or water. The paper addresses itself to physical properties of germanium and structural parameters of windows and their mountings that must be considered in the successful design of germanium windows for external pressure service.
Passive infrared optical systems sensitive to 8-12μm radiation have been produced for the military for over fifteen years. Gradually, the demand for greater resoution and sensitivity have led to more complex designs. Where previous systems utilized simple germanium optics, present systems use more than one optical material to enable the optical designer to produce color correction over the 8-12μm wavelength range. One class of optical materials extensively utilized for this purpose are infrared transmitting glasses. The glasses used are melt formed, cast or slumped to shape much like any other optical glass. The methods of preparation and fabrication will be presented. Physical parameters important to their optical application will be given and compared to the industry standard, germanium. Methods used in their characterization will be discussed.
SHIVA, the 10-kilojule Neodymium-glass laser for the High Energy Laser Facility at Lawrence Livermore Laboratory has been built, exceeded minimum energy predictions, and is currently being applied to laser fusion experiments. The twenty, 20-cm aperture arms con-tain a total of about 1500 optical components for beam propagation, and another 1000 elements are used for control systems and diagnostics. In order to focus the energy on targets smaller than 1 mm in diameter, it has been necessary to maintain very high optical quality throughout the system. The manufacturing and testing technologies involved in meeting this challenge have been noteworthy and have encompassed glass manufacturing, optical finishing, and coating, for elements as diverse as Faraday rotators, laser rods and disks and aspheric lenses.
Recently, by combining brazing technology with lightweight beryllium detail components, ultra-lightweight beryllium optic substrates have become available to the designer. Two basic approaches are discussed, in the paper which includes an "eggcrated" core technique where thin. beryllium sheet products are "photo-etched" into an eggcrated pattern. and metallurgically brazed to face plates. Details of core configuration, fabrication, brazing and tolerances that can be achieved, will be discussed. Actual hardware will be reviewed from 4" to 19" assemblies. Other applications involving machined. beryllium halves will be discussed. Various techniques of metal removal yielding an overall bulk density from 33% to 5%. Joining techniques to close out the hollowed. substrate are discussed. Applications from 6" to 36" diameter optics will be reviewed. Non-destructive inspection. techniques and extrapolations to larger substrHtes of both types of designs will be reviewed.
This paper describes the design analysis, hardware fabrication and tests performed on a compact four-mirror optical system. This optical system is part of a small, lightweight infrared sensor capable of quick cooldown and interfacing with scan gimbals. During the development of this system, many fabrication techniques have been advanced. The combination of new techniques in design analysis and beryllium mirror fabrication at Honeywell Electro-Optics Center resulted in a sensor whose image quality is maintained over a wide temperature range and during unusual dynamic environments. This paper is an overview of the qualifications of a Compact Four-Mirror Optical System.
The intent of this paper is to provide a comprehensive overview of the optical factors which affect system choice in 10μ imaging applications. Illustrative design alternatives are developed and discussed. Single element designs, refractors, reflectors, and catadiop-tric designs are described and compared. Diffraction-limited performance is explained and predictions made of real-world performance. Production tolerances, and a method for predicting degradations experienced in mass production are presented. Radiometric aspects are left for subsequent papers.
The report of the Precision Machined Optics Ad Hoc Committee to the Manufacturing Technology Advisory Group is presented. The committee identifies a technology implementation barrier and recommends several DoD funded programs to help solve the problem.
Germanium is found as an impurity in minerals closely associated with zinc-lead ores. Production of these major metals in the smelting process results in residues containing by-products including germanium. The techniques and economical considerations for producing germanium metal is briefly discussed along with its consumption and future forecasts both for the U.S.A. and the rest of the world.
There has been a growing need to expand infrared radiometric investigations from military and space applications to areas such as the thermal behavior of glass, plastics, oils, flames and other substances whose infrared characteristics vary with thickness, composition and wavelength. Unfortunately, potential industrial and academic investigators have not had the funds available to their military and aerospace counterparts. The need, then, was for a multispectral instrument specifically designed for the infrared which would be stable, absolutely calibrated and versatile enough to accomplish the above measurement tasks, yet affordable to the industrial or academic researcher. This paper traces the development of the 12-880 Precision Filter Radiometer which developed as a reconfiguration and expansion of a standard dedicated infrared thermometer. The instrument's unique, highly stable thermal/optical design made this development possible. Several proven applications are discussed as well as a number of potential applications for the new instrument.