The Honeywell Radiation Center is a supplier of electro-optical components and systems which detect and track targets, image scenes, and measure radiation in the visible and infrared regions of the spectrum. In particular, it develops and constructs spaceborne spectroradiometers, star trackers, sun sensors, thermal inaging systems, oculometers, and interferometric spectrometers, and detectors.
In this paper we describe the design and performance of a Multispectral Scanner. The optical system of Skylab Multispectral Scanner (S-192) consists of an image plane scanner (telescope), a spectrometer for separation of the radiation into 13 spectral bands, and a 13-element (Hg,Cd)Te detector array. The image plane scanner is a new system based on three interrelated main features: (1) a reflective adaptation of the Schmidt principle; (2) a conical line scan in which all field elements are brought to and corrected on axis; and (3) a scanning arrangement in which the aperture stop of the system, located in a relay unit, is imaged at the center of curvature of the spherical primary mirror. Replacing the physical stop used in the classical Schmidt configuration with a virtual one makes the system much more compact. As a consequence of the image plane scanning and the Schmidt symmetry, the system scans at a large radial angle (11-degree diameter) and at an extremely high rate (6000 rpm) with relatively small scanning mirrors and a large entrance pupil diameter (43 cm). The spectrometer divides the radiation into 13 spectral bands, 12 of which are located between 0.4 and 2.35 micrometers and the other, 10.2-12.5 micrometers. A dichroic beamsplitter separates the far IR band from the 12 lower wavelength bands, which are dispersed by prisms. Photographic reproductions of the actual flight recordings show 80-meter resolution at an altitude of 440 km.
The statistical technique of photon ray tracing, commonly known as the Monte Carlo Method, has been successfully used on numerous radiant transport problems. Because of its simplicity, the method can be applied to complex systems which are otherwise not amenable to a conventional approach such as the solution of integral-differential equations. The primary limitation of the method is the wide ranging complementary techniques necessary in reducing the amount of computations in each analysis. This paper presents such a technique that can be used in the analysis of radiant interchange. Applied to an optical system, the method can be used to solve for image quality, system attenuation, off-axis energy rejection, and thermal radiation heat transfer. Results of three demonstrative examples are also presented.
The Lower Atmospheric Composition and Temperature Experiment (LACATE) is a development program within the Advanced Application Flight Experiments (AAFE) Project Office at the NASA Langley Research Center. The ultimate objective of the LACATE is to determine the vertical distribution of certain atmospheric constituents and temperature on a global scale from the upper troposphere through the stratosphere and into the lower mesosphere. In this paper, we describe a program being conducted to provide a demonstration of experiment feasibility on a balloon flight test to be conducted by the NASA.
The frequency dependence of responsivity and detector noise for (Hg,Cd)Te detectors operating in the 8-14 pm region at 77°K was investigated. The results showed that these quantities have the same frequency dependence and corner frequency. Values of f* were thus experimentally determined and found to be >10 MHz for detectors that have D*X - 5 X 1010 cm Hz% Watt-1. The results are shown to be consistent with a simple photoconductive theory based on the assumption of equal lifetimes for holes and electrons.
(Hg,Cd)Te material and photodiode fabrication processes have been developed to provide high performance detectors for a wide range of system applications. Major emphasis has been placed on detectors for 10.6-micrometer laser detection, although detectors have been designed and fabricated to cover the infrared spectrum between 1.5 and 14 micrometers. Since the principal laser source being considered for optical communications is the CO2 laser at 10.6 micrometers, factors affecting detector performance for this wavelength are the subject of this paper. This paper discusses basic material considerations, doping concentrations and carrier transport which affect photodiode performance. Additionally, tradeoffs in photodiode design for specific applications are presented together with predicted performance based upon expected refinement in material and process technology.
An interferometer spectrometer rocket payload system to measure infrared auroral emissions from 5 to 22 micrometers has been in design and development for several years. System specifications for wavelength coverage and sensitivity require that the instrument must function at cryogenic temperatures. This paper will describe the scanning Michelson interferometer system, together with the optical, electronic and cryogenic methods employed to achieve an operational sounding rocket experiment and its successful field test.
An Ali_xGaxAs, injection laser has been employed as a reference source in a rapid scan cryogenic interferometer spectrometer. The interferometer was designed to operate at 20°K with a scan velocity of 1 cm/sec and a spectral resolution of 2 cm-1. The slide velocity control and sampling requirements for a continuous drive interferometer are discussed and those properties which are needed in choosing and calibrating an injection reference laser are given. The relative advantages and limitations of an injection reference laser are given and are related to the laser's spectral purity, threshold condition, power efficiency, and beam pattern.
The near-axis scatter of infrared (10.6 µm) energy from high reflectivity metal mirrors is described. Effects of contamination on the scatter are described. Methods of evaluating various forms of contamination are presented and selected data are presented. Finally, the recording techniques for surface characteristics photographically are described along with a typical photograph of a large aspheric mirror.
The far field energy distribution of a 10.6 u laser beam can be altered by optical means to favorably match the field of view of an imaging system with a linear array of detectors. In this paper we describe a laser beam shaper which consists of an anamorphic optical system and a X/2 phase step which is introduced into the central part of the laser beam. It is shown that with proper design, most of the laser energy can be made to fall within the field of view of the linear array and with nearly equal distribution among the detectors.
In this paper we describe a new Forward Looking Infrared (FLIR) development. Two basic types of scanning are presently representative of most FLIR systems, parallel scanning and serial scanning. Historically, the first high performance FLIRs utilized parallel scanning. The recent development of (Hg,Cd)Te detectors has made possible the use of serial scanning. This paper describes a serial scanned TV-compatible FLIR.
In this paper, we describe an Oculometer which is an electro-optical device that measures eye direction (and fixation point coordinates) without attachment to, or clamping of, the subject. By virtue of its special optical characteristics, the same basic system can be configured for operation very close to the subject, as in a head mounted system, and also at a distance of several feet or more from the subject. The basic signal processing operation is the same for all configurations, and is performed by a standard minicomputer. It is also shown that additional signal processing, as required in certain configurations and applications, can be added as a separate software module to the general Oculometer software.
Requirements sometimes exist for the measurement and/or detection of weak optical sources in the vicinity of bright sources. Capability of observing weak optical sources is dependent on the system sensitivity which is limited by the detector D*, processing electronics noise, mechanically coupled scan or jitter noise, thermal effects on the detector sensitivity, optical emissions of sensor housing and imaging optics, and the point spread function. The point spread function is mainly governed by the optical element size, shape, and aberrations. When a strong source is in the proximity of the weak signal, the wings or roll offs of the point spread function play an important role in the system detection capability. Two factors dominate the roll offs, namely diffraction and scattering of the optical train. This paper discussed the point spread function requirements or conversely, the out-of-field rejection requirements needed to suppress the unwanted sources, small or large in angular extent, to a level tolerable to the system. Stray light sources are discussed and suppression designs considered.
Local reference beam holography can be used in conjunction with interferometry to determine the complex amplitude distribution in the output of CW and pulsed laser beams. A hologram is recorded of the laser wavefront with a locally generated reference beam from the laser beam to be measured. The wavefront is then reconstructed with a CW laser beam in the usual way. The modulus of the complex amplitude can be measured directly and the phase is measured by interfering the reconstructed wavefront with a uniform phase wavefront. If the laser output is partially coherent the possibility exists of extending this method to determining the mutual intensity function and the complex degree of coherence of the laser wavefront.
A successful beryllium reflector applicable to land-, sea-, air- and spaceborne surveillance systems is the culmination of a joint effort between the Customer and the Manufacturer. It involves interfacing contributions from Engineers in a number of disciplines such as systems, optics, stress analysis and, most importantly, machining. It requires the knowledge of the characteristics and the experience in the special handling technology of beryllium. It demands that the Manufacturer has an appreciation of the End-User's system requirements and that the Customer has an awareness of the Producer's expertise and potential in order to achieve a feasible production design specification of a metal optic. The average mirror density within the envelope of a mass relieved beryllium optic is about 0.6 g - cm-3. The essential steps from concept through design analysis and manufacture of a typical stiff, beryllium, low inertia, lightweight 1 kilogram (2.2 lb), active plane mirror 35.6 cm X 21.6 cm X 2.7 cm (14" X 81/2" X 11/16"), are presented.
An improved method of measuring spatial coherence is described and some sources of measurement errors are discussed. Partial coherence in the image plane of an optical system is discussed and results of coherence measurements are given that demonstrate the scaling of the coherence function for coherence intervals large compared to the diameter of the Airy disk and the limiting value for the coherence interval equal to the diameter of the Airy disk. The application of these results to microdensitometry is discussed and results of coherence measurements in the source plane of currently-used classical microdensitometers are given.
For over a decade, passive thermography has been utilized as a reasearch aid in the study of human breast cancerl . In this case, a passive thermographic system basically performs a spatial measurement of the 'natural thermal emission (heat) of the human body. The measured flux is then converted into an electrical signal, displayed, and recorded (generally on photographic film). Al-t hough passive thermography has proved to be of great value in diagnostic', work, there are limitations on its effectiveness. One such limitation is the thermographic system's inability to yield significant information relating to the depth of various portions of the breast's vascular tree. Efforts are currently in progress to overcome this problem by utilizing a technique called active-passive thermography. Before discussing this technique, the question of why the depth information is of importance is addressed.