Optical properties of polycrystalline diamond films in the far-infrared

Room temperature Fourier transform spectroscopic transmissivity data in the far-infrared (10 360 cm-1) were used to derive a model for the complex refractive index (n ik) of polycrystalline diamond films grown by microwave plasma enhanced chemical vapor deposition. Transmission measurements were also made at a frequency of 19.5 cm-1 utilizing a CO2 optically pumped submillimeter laser. Due to their polycrystalline nature, the diamond films exhibited a surface roughness with crystallite sizes ranging from 2 8 μm. This roughness introduced a diffuse scattering loss at the shorter wavelengths and is accounted for in the determination of the optical properties of the diamond. Residual absorption, proportional to λ2, is observed at longer wavelengths (1/λ < 100 cm-1).