The infrared emittance and transmittance spectra of a chemical vapor-d
eposited diamond substrate were determined at 4.2, 77 and 295 K. The m
ultiphonon region was analyzed under varying degrees of spectral resol
ution. No variance in spectral properties over this temperature range
was observed beyond measurement uncertainty. The refractive index of t
he material was determined in the 3-21 micron spectral region at cryog
enic 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 va
por-deposited diamond possesses significant potential for use as windo
ws, filter substrates and optical component coatings in long-wave infr
ared systems.