Laser damage characteristics and nanosecond laser conditioning of multilayer dielectric gratings for picosecond-petawatt laser systems

Multilayer Dielectric Gratings (MLDGs) are the core optics of the picosecond-petawatt laser systems based on Chirped Pulse Amplification (CPA). The MLDGs encounter nanosecond- and picosecond-laser irradiation during the broadening and recompression of the laser pulse in CPA. Therefore, a comprehensive evaluation of the laser-induced damage performance of MLDG in the nanosecond (ns) and picosecond (ps) regimes is required. Herein, we examined the laser damage characteristics of MLDGs induced by the 8-ns and 8.6-ps laser pulses. In the two tested laser pulse widths, the damage of the MLDG was dominated by the nano absorbing defects and nodular defects, but the damage mechanism has changed. When the laser pulse width is shortened from ns to ps, the damage sites caused by the absorbing defects transfer from the interface to the grating pillars, where there is the maximum electric field. And the nodular ejection pit changes from a complete eruption to a local damage corresponding to the electric field enhancement region. For the nodular defects, ns-laser conditioning was introduced for removing them and achieved a maximum enhancement of 40% in the ps laser-induced damage threshold.