High temperature infrared absorption of CVD diamond measured by laser calorimetry

The infrared absorption of CVD diamond at a wavelength of 10.6 mu m was measured as a function of temperature between 20 and 500 deg C. CVD diamond of different structural quality was investigated. Optical spectroscopy and infrared Raman scattering were used for the structural characterization. Laser calorimetry was applied to measure the IR absorption at elevated temperatures. For these measurements, CVD diamond devices with integrated heater and temperature sensor were prepared. The optical absorption at a given temperature was determined by comparing the temperature rise induced by CO2 laser irradiation with the equivalent electrically induced temperature rise. Samples with a room temperature absorption coefficient of alpha=0.096 cm-1 and alpha=0.85 cm-1 were investigated. Despite this large difference, the absolute increase of the absorption coefficient with increasing temperature was found to be similar for the two samples. It increased by a value of about 0.5 cm-1 between 0 and 500 deg C.