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Thermal process of laser-induced damage in optical thin films

Thermal process of optical thin film irradiated by laser is a fundamental process for laser induced damage. The energy deposition in thin film is induced with built absorption, defect absorption, multi-photon absorption, or avalanche ionization in thin film. Thus, the temperature is increased in the absorption site and a heat source is formed. The heat is transferred to another region through heat conduction. The interaction process of laser and thin film is very complex. This film is breakdown when the temperature is raised to a definite value. Thermal process of optical materials was researched by some authors. But detailed research about the thermal process of multilayers was very few. Presented in this paper are the theoretical formula and calculation results of temperature distribution in multilayer. In situ process of interaction between laser and thin films was monitored by photothermal deflection technique. The theoretical analyses are consistent with the experimental results.