To study in a non destructive way absorbing localized defects initiating laser damage in optical components, we implement a microscopy set-up with high spatial resolution and high detectivity, based on photothermal deflection method and combined with a laser damage test set-up.First, optimal configuration is determined thanks to a bibliographical study, a feasibility study and a theoretical comparative study.In other respects, the role of wavelength on absorption of defects is characterized thanks to a study of spectral properties of absorbing and scattering defects in the UV, visible and IR ranges, for substrates and thin films.Then, we present the experimental realization of the new set-up. A sub-micronic spatial resolution is obtained.Finally, this new set-up is applied to the study of gold inclusions of 600 nm embedded in silica. We demonstrate the existence of a “pre-damage” phenomenon: the absorption of inclusions decreases after laser irradiation without any surface alteration.
