Effect of pulse duration on laser induced damage threshold of multilayer dielectric gratings

Abstract

Multilayer dielectric gratings (MDGs) are more and more used to compress pulse in the next generation of chirped-pulse amplification (CPA) system for high-energy petawatt (HEPW)-class lasers due to their high efficiency and high damage threshold for picosecond pulses. The damage tests for MDGs were carried out with long pulse (12ns) in air and short pulse (0.66~9.7ps) in vacuum at 1053nm, respectively. The experiment methodologies and results were discussed. For both long and short pulse, the initial damage locates at the grating ridges opposite to the incoming wave, which is consistent with the maximum normalized electric field intensity (NEFI). For long pulse, the damage is characterized by melting and boiling. And for short pulse, the damage is ascribed to multiphoton-induced avalanche ionization because of the electric field enhancement in the grating groove structure. And Measurement results of the dependence of damage threshold on the pulse width are presented. And the damage threshold of MDG in beam normal is 4.4J/cm² at 70° incidence angle for 9.7ps pulse.