Photothermal deflection spectroscopy for the study of thin films and optical coatings: measurements of absorption losses and detection of photoinduced changes

Mireille Commandre; Pierre J. Roche; Gerard Albrand; Emile P. Pelletier

doi:10.1117/12.20367

1 August 1990 Photothermal deflection spectroscopy for the study of thin films and optical coatings: measurements of absorption losses and detection of photoinduced changes

Mireille Commandre, Pierre J. Roche, Gerard Albrand, Emile P. Pelletier

Author Affiliations +

Proceedings Volume 1270, Optical Thin Films and Applications; (1990) https://doi.org/10.1117/12.20367
Event: The International Congress on Optical Science and Engineering, 1990, The Hague, Netherlands

Abstract

Photothermal deflection has been used to map the absorption characteristics of thin film optical coatings. Our experimental set-up can give low level absorption coefficient down to 1 ppm, with a spatial resolution limited by the excitating laser beam diameter (100 tim). On single layer films, we can calculate extinction coefficient of the deposited material with a detectivity of a few i07. We present a study of absorption losses in single layer titania films and in TiOWSiO2 Fabry-Perot filters prepared in our laboratory by electron beam evaporation, ion assisted deposition and ion plating. Local variations of absorption on the sample surface can be very large especially in lowly absorbing samples; high absorption sites may be related to local defects responsible for laser damage. Furthermore, we show that some titania films can present photoinduced instabilities. Photothermal deflection spectroscopy is a good way to study absorption evolution under illumination. In Ti02/Si02 Fabry-Perot filters, we have observed that these absorption changes are associated with important drifts of transmission curves. So these instabilities can be explained by a change of the value of the complex index Ii = n - ik. Results lead to the conclusion that stability under illumination is strongly correlated to the deposition technique and also to the deposition conditions: unstable samples are mostly prepared by electron beam evaporation.

Citation Download Citation

Mireille Commandre, Pierre J. Roche, Gerard Albrand, and Emile P. Pelletier "Photothermal deflection spectroscopy for the study of thin films and optical coatings: measurements of absorption losses and detection of photoinduced changes", Proc. SPIE 1270, Optical Thin Films and Applications, (1 August 1990); https://doi.org/10.1117/12.20367

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