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Proceedings Paper

Solid state modulator for thermal imaging applications
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Paper Abstract

The staring array is the basis of many modern thermal imaging systems, cooled and uncooled. A major drawback in all staring array thermal imaging systems is the need to provide thermal referencing in order that the non-uniformity inherent in all IR detector technologies can be corrected. A common approach is to use a mechanical shutter operated intermittently, typical of uncooled resistance bolometers and cooled photon detectors, or a rotating chopper, typical of ferroelectric uncooled bolometers. Although these methods are inexpensive and consume little power, they are inappropriate to environments where high g-forces or shock loads are encountered. This paper describes a solid state modulator operating on the 8-12micrometers band. The modulation mechanism is induced absorption in high-purity intrinsic germanium. Electron-hole pairs are created in the germanium modulator; the electrons are weak absorbers but the holes absorb strongly by means of the light-hole/heavy-hole inter-sub-band transition. The transmission of the modulator can thus be varied by varying the hole concentration, for example by illuminating the modulator with near IR light. Very good modulation depth (5% to 90% transmission) has been measured, at optical power densities of approximately 10 W/cm2. Switching speeds are controlled by the carrier lifetime, and are a few milliseconds in our prototype device. The high power requirement rules out this approach for hand-held applications. However for intermittent use, or where the environmental constraints are dominant, this technology offers a potentially robust 8-12micrometers modulator.

Paper Details

Date Published: 15 December 2000
PDF: 12 pages
Proc. SPIE 4130, Infrared Technology and Applications XXVI, (15 December 2000); doi: 10.1117/12.409870
Show Author Affiliations
Paul Antony Manning, Defence Evaluation and Research Agency Malvern (United Kingdom)
Peter Fairley, Univ. of Southampton (United Kingdom)


Published in SPIE Proceedings Vol. 4130:
Infrared Technology and Applications XXVI
Bjorn F. Andresen; Gabor F. Fulop; Marija Strojnik, Editor(s)

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