Abstract

We review the principle of photothermal deflection for measuring absorption losses in TiO₂ films. A collinear arrangement gives the best sensitivity for the detection of losses in a low absorbing film deposited on a transparent substrate. The nineteen TiO₂ films produced by seven different processes (electron-beam evaporation, ion assisted deposition, ion beam sputtering, ion plating) of the 1986 OSA Annual Meeting are measured by this technique. The extinction coefficients of the different films do not show obvious correlation with the deposition method. An important fact is that we have detected a variation in absorption as a function of time on some layers. This absorption shift is connected with the illumination conditions of the sample under study (wavelength, 600 nm; incident power, 750 W/cm²). Experimental results over time are given. The evolution of the photothermal signal is very different from one sample to another. This phenomenon is partially reversible and can be modified by annealing.

© 1988 Optical Society of America