Optical Absorptivity of Diamond Powders and Polycrystalline Films

Optical absorptivity of diamond powders and polycrystalline CVD films have been obtained by using photoacoustical spectroscopy in the spectral diapason from 200 to 1500 nm with different light modulation frequencies (from 20 to 1500 Hz). The both powders and films demonstrate spectral features corresponded to fundamental absorption edge near the diamond band gap (5.5 eV) and optical absorption in visual light region which was similar to one in neutron or electron irradiated single diamond. Specific "downfall" in optical absorption have been detected in UV region for powders and polycrystalline films with smallest diamond crystallites. The spectra dependence from light modulation frequency allow to conclude that UV "downfall" is due to mirror light reflection from randomly oriented diamond grains.