Influence of defects on the femtosecond laser damage resistance of multilayer dielectric gratings

Multilayer dielectric (MLD) gratings with high diffraction efficiency and a high laser-induced damage (LID) threshold for pulse compressors are key to scaling the peak and aver-age power of chirped pulse amplification lasers. However, surface defects introduced by manufacturing, storage, and handling processes can reduce the LID resistance of MLD gratings and impact the laser output. The underlying mecha-nisms of such defect-initiated LID remain unclear, especially in the femtosecond regime. In this Letter, we model dynamic processes in interactions of a 20-fs near-infrared (NIR) laser pulse and a MLD grating design in the presence of cylindri-cally symmetrical nodules and particle contaminants and cracks at the surface. Utilizing a dynamic model based on a 2D finite difference in time domain (FDTD) field solver cou-pled with photoionization, electron collision, and refractive index modification, we study the simulation results for the damage site distribution initiated by defects of various types and sizes and its impact on the LID threshold of the grating design.(c) 2023 Optica Publishing Group

Automated summary

Multilayer dielectric (MLD) gratings with high diffraction efficiency and a high laser-induced damage (LID) threshold are crucial for pulse compressors in chirped pulse amplification lasers. However, surface defects introduced in the manufacturing process can decrease the LID resistance of MLD gratings and affect laser output. In this study, a dynamic model is used to investigate the impact of defects, such as nodules, particle contaminants, and cracks, on the LID threshold of a MLD grating design using a 20-fs near-infrared (NIR) laser pulse.