Measurement of optical absorption in polycrystalline CVD diamond plates by the phase photothermal method at a wavelength of 10.6 μm

A highly-efficient phase photothermal method is developed for quantitative measurements of the small optical absorption coefficient in thin plates made of highly transparent materials in which bulk losses significantly exceed surface losses. The bulk absorption coefficient at 10.6 μm is estimated in polycrystalline diamond plates grown from the vapour phase (a CVD diamond). The results are compared with those for natural and synthetic diamond single crystals and with the concentrations of nitrogen and hydrogen impurities. The absorption coefficient of the best samples of the CVD diamond did not exceed 0.06 cm^-1, which, taking into account the high thermal conductivity of the CVD diamond (1800 – 2200 W mK^-1 at room temperature), makes this material attractive for fabricating output windows of high-power CO₂ lasers, especially for manufacturing large-size optics.