Modeling of the femtosecond pulsed laser-induced damage of multi-layer dielectric gratings

The laser damage resistance of multi-layer dielectric gratings (MDGs) and metal multi-layer dielectric gratings (MMDGs) for femtosecond lasers directly determines the performance and life span of the high-energy laser system. It remains a significant challenge to predict the laser-induced damage threshold (LIDT) of MDGs and MMDGs for femtosecond lasers. Based on the nonlinear ionization and electric field intensity model, an effective method is proposed to calculate the LIDT of MDGs and MMDGs by introducing the dual temperature model. We take into account the evolutions of thermophysical parameters including the absorption coefficient, heat capacity, and thermal conductivity of the dielectric material as a function of the free-electron density and temperature. The free electron density of the conduction band combined with the electric field strength inside the grating can be calculated by the laser-induced ionization theory, more importantly, the transient distribution of the lattice temperature field generated by femtosecond laser irradiated grating excitation is obtained by the twotemperature model (TTM). This work is beneficial for guiding the design and fabrication of MDGs and MMDGs with high-LIDTs for ultra-short ultra-intense laser systems.