The quasi-parallel collinear photothermal deflection (PTD) technique was ap
plied 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 absorp
tion in CVD diamond to be studied. For the measured samples, the optical ab
sorption 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 relati
ve PTD Values were calibrated by using a sample with known absorption (meas
ured by laser calorimetry). The mathematical simulations were carried out u
sing a theoretical model for the temperature (heat diffusion) profile in di
amond, which yielded a very good agreement with the experimental results. (
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