Absorption and damage threshold measurements of optical coatings

The determination of absorption at the wavelengths 1.06 and 10.6 micrometers was carried out by means of the photothermal displacement spectroscopy method. The analysis of the signal generation demonstrates the necessity of comprehensive correction calculations to obtain the absolute values. The investigation of the influence of postdeposition baking on the absorption revealed the generation of absorption centers in consequence of the heat treatment, e.g., at Ta2O5 films. The deposition of BaF2 films at the substrate temperature 150 degree(s)C for 10.6 micrometers wavelength led to a smoother absorption behavior and simultaneously to a reduction of scattering compared to deposition at room temperature. Damage threshold measurements at the wavelength 248 nm also proved the negative influence of postdeposition baking on the coating performance. Further experiments in the ultraviolet wavelength range tested the association of laser damage thresholds of the high index material and the multilayer system.