TIR based photothermal / photoacoustic deflection

Abstract

We report on a new experimental technique for monitoring laser-induced shock waves and thermal waves above the sample surface called total internal reflection based photothermal / photoacoustic deflection (TIR based PAD/PTD deflection). It is based on the changes in transmissivity of a prism which is operated near the TIR condition for a HeNe laser beam. The HeNe laser beam is probing photoacoustic or photothermal waves originating from a sample surface due to interaction with a pulsed Nd:YAG laser beam. The method is compared with standard online detection techniques like scatter probe monitoring and plasma detection, and found to be a very sensitive and practical tool. It also showed its suitability for selectively monitoring several surfaces (e. g. front and rear surface) of optical components, and attributing the damage starting point. Therefore, the method might be used for monitoring of surface damage on laser crystals or valuable components.