LWIR spectral properties of CVD diamond at cryogenic temperatures

The infrared emittance and transmittance spectra of a chemical vapor-deposited diamond substrate were determined at 4.2, 77 and 295 K. The multiphonon region was analyzed under varying degrees of spectral resolution. No variance in spectral properties over this temperature range was observed beyond measurement uncertainty. The refractive index of the material was determined in the 3-21 micron spectral region at cryogenic temperatures. The absorption coefficient was also determined and shown to vary from 11.7 cm(-1) in the short wave 2 phonon region to 0.79 cm(-1) at longer wavelengths. The results indicate that chemical vapor-deposited diamond possesses significant potential for use as windows, filter substrates and optical component coatings in long-wave infrared systems.