Optical and thermo-optical properties of chemical vapor deposited (CVD) diamond

Natural diamond is a material with excellent optical and thermo-optical properties, but limited to small sizes. However, the advent of CVD techniques made large area diamond available. For the deposition of CVD diamond windows we have used a novel microwave plasma system with an ellipsoidal reactor, that allows the deposition of high quality CVD diamond on substrates up to 6 in. in diameter. Free standing polished diamond windows were investigated with respect to optical transmission and scattering losses. New techniques have been developed for measuring the thermo- optical properties of CVD diamond. Special care was taken to reduce sample preparation. The IR - absorption coefficient between 9 and 11 mu m has been measured using a novel laser calorimetry setup. By successive thinning the diamond sample, both the local absorption coefficient and the surface absorption were derived. The thermal diffusivity was obtained by applying a new technique, based on electrically induced thermal waves. We found that high quality CVD diamond almost reaches the thermo-optical properties of the best natural diamonds (type IIa).