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 six different processes (electron beam evaporation, ion assisted deposition, ion beam sputtering, ion plating, …), discussed at the 1986 Optical Society of America 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: 400 W/cm2). Experimental results over time are given. The evolution of the photothermal signal is different from one sample to another. This phenomenon is partially reversible and depends on moisture degree of atmosphere.
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