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Proceedings Paper

Operation Of An Intermediate Temperature Detector In A 10.6 µm Heterodyne Rangefinder
Author(s): D J Wilson; R Foord; G.D. J Constant
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Paper Abstract

CO2 laser rangefinders have been used for some years to complement the operation of 8 to 12um thermal imaging systems. Being wavelength compatible they can range on to any point in the thermal scene, and have the added advantage of being eye safe.' Using coherent detection and operating the laser in a CW mode the rangefinder can also provide information on target movement in the form of Doppler shifts which produce frequency modulation of the carrier. This enables acquisition of velocity and vibration data. Other options can include active imaging by use of an add on scanner and anemometry for air turbulence studies.2 Systems of this type normally use a low power, (up to 10 watts) frequency stable CO2 laser, a modulator to superimpose any carrier frequency code on the laser beam and a cooled detector, normally a Cadmium Mercury Telluride photo-diode operating at 77K. These detectors have a high quantum efficiency, and a frequency response which can be well in excess of 1GHz. One disadvantage is that the detectors require Joule-Thompson or engine cooling; this results in added bulk due to high pressure gas cylinders or compressor, with consequent extra capital and running costs. These systems would be more attractive and versatile if this inconvenience could be avoided by running at higher temperatures. With direct detection, higher temperatures result in a rapid degradation of performance due to reduction in detectivity. Heterodyne detectors, thermoelectrically cooled to about 190K, offer convenience without as large a penalty, due to their greater dependance on quantum efficiency. This paper describes the design of a Cadmium, Mercury Telluride p-type photoconductive detector with its associated thermo-electric cooler, bias supply and amplifier in a complete package. Performance under both laboratory conditions and in a laser rangefinder is discussed and results are compared, with a photo-voltaic detector,operating at 77K using a joule-Thompson cooler.

Paper Details

Date Published: 6 October 1986
PDF: 4 pages
Proc. SPIE 0663, Laser Radar Technology and Applications I, (6 October 1986); doi: 10.1117/12.938668
Show Author Affiliations
D J Wilson, Royal Signals and Radar Establishment (United Kingdom)
R Foord, Royal Signals and Radar Establishment (United Kingdom)
G.D. J Constant, Royal Signals and Radar Establishment (United Kingdom)

Published in SPIE Proceedings Vol. 0663:
Laser Radar Technology and Applications I
James M. Cruickshank; Robert C. Harney, Editor(s)

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