DIAMOND WINDOWS FOR IR APPLICATIONS IN ADVERSE ENVIRONMENTS

Diamond exhibits an unusually favorable combination of properties in terms of its mechanical strength, thermal conductivity and optical transmission, which makes this material highly attractive for IR applications that involve severe environmental conditions. The objective of this paper 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 use as missile domes in the mid-IR; at longer wavelengths, it can be expected that single-phonon absorptions will be tolerable in the sense that self-emission at elevated temperatures should not degrade the signal-to-noise ratio. In addition to surface hardness, the features that confer diamond its advantage are its high thermal conductivity and low thermal expansion, which indicate that diamond has orders of magnitude more thermal shock resistance than the best competing materials. 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 (up to about 1 MW) will be limited by thermally induced optical distortion, which can only be eliminated if absorption-free, anti-reflection coatings become available, and the edge heat transfer coefficient, which must be greatly enhanced to take advantage of the exceptional thermal conductivity of diamond at low temperatures.