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Proceedings Paper

Diamond windows for the infrared: fact and fallacy
Author(s): Claude A. Klein
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Paper Abstract

Diamond exhibits an unusually favorable combination of properties in terms of mechanical strength, thermal conductivity, and optical transmission, which makes this material highly attractive for infrared (IR) applications that involve severe environmental conditions. Until recently, diamond has been available only in the form of relatively small crystals, but this situation is evolving rapidly as a result of major advances in the art of growing diamond by low-pressure chemical vapor deposition (CVDI techniques. Success in producing large, free-standing deposits with properties that match those of natural diamond has stimulated enormous interest and has given rise to much speculation about CVD diamond as an "ideal" optical material for a wide range of engineering uses in the IR: there are. however, limiting factors that must be taken into consideration. The objective of this Critical Review is to provide an initial assessment of some of the issues that arise in connection with the use of diamond artifacts for two highly demanding tasks: domes for high-speed missiles and windows for high-power lasers.

Monolithic diamond deposits lack the degree of transparency required for operation as transmissive optics elements in the mid-IR: at longer wavelengths (LWIR), it can be reasonably expected that singlephonon absorptions will be tolerable in the sense that self-emission phenomena at elevated temperatures should not be catastrophic. Besides surface hardness, the features that confer diamond its advantage are the high thermal conductivity and the low thermal expansion, which indicate that diamond has orders of magnitude more thermal shock resistance than some of the best competing materials. There is little doubt that the "new diamond" technology will provide a credible, if not outstanding LWIR dome material for tactical missiles operating at speeds up to but not beyond Mach 4 in the atmosphere.

Defect-free, single-crystal diamond also emerges as a promising candidate material for high-average-power laser window applications in the near-IR. The power-handling capability (<1 MW independently of the window size! will be limited by la) thermally induced optical distortion, which can only be eliminated if absorption-free anti-reflection coatings become available, and (b) the edge heat-transfer coefficient, which must be greatly enhanced to take advantage of the exceptional thermal conductivity of diamond at low temperatures. Pressure-induced and thermally-induced stresses are of no consequence, but peak laser intensities in excess of, say 1 GW/cm2 should be avoided because of unfavorable non-linear refractive index characteristics.

Paper Details

Date Published: 1 October 1991
PDF: 40 pages
Proc. SPIE 10260, Infrared Optical Design and Fabrication: A Critical Review, 102600C (1 October 1991); doi: 10.1117/12.48452
Show Author Affiliations
Claude A. Klein, Raytheon Co. (United States)


Published in SPIE Proceedings Vol. 10260:
Infrared Optical Design and Fabrication: A Critical Review
Rudolf Hartmann; Warren J. Smith, Editor(s)

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