Measurement and mapping of very low optical absorption of CVD diamond IR windows

Abstract

The quasi-parallel collinear photothermal deflection (PTD) technique was applied to the investigation of the optical absorption coefficient at the CO2 laser wavelength (10.6 mu m) for a set of chemical vapour deposited (CVD) diamond windows of various optical qualities. The PTD measurements enabled absorption imaging to be performed and thus the mechanism of optical absorption in CVD diamond to be studied. For the measured samples, the optical absorption is affected by the black non-diamond inclusions, which are - to a greater or lesser extent, depending on the material grade - present in all CVD diamond films. The optical grade material contains just a few of these inclusions. To obtain absolute values of the optical absorption, the relative PTD Values were calibrated by using a sample with known absorption (measured by laser calorimetry). The mathematical simulations were carried out using a theoretical model for the temperature (heat diffusion) profile in diamond, which yielded a very good agreement with the experimental results. (C) 2000 Elsevier Science S.A. All rights reserved.