A theoretical investigation of the laser damage threshold of metal multi-dielectric mirrors for high power ultrashort applications.

An approach for the theoretical evaluation of the damage threshold in optical interference coatings that combine metal and dielectric films is presented. The model that is used combines a matrix formalism to describe the film system with the two temperatures model that describes the energy transfer and the temperatures of electrons and lattice in a solid submitted to a laser irradiation at the femtosecond time scale. With this approach the thermal consequences due to the ultrafast absorption of the metal film can be evaluated in the multilayer stack for single or multiple pulses. Some applications are presented for the case of broadband mirrors for ultrashort pulses with low dispersion. Particularly we study the impact of the metal film (metal element, thickness) and the design on the Laser Induced Damage Threshold in the sub picosecond regime.