Damage characteristics of pulse compression grating irradiated by a nanosecond laser

Abstract

Multilayer dielectric gratings (MLDGs) have been widely used for pulse compression in chirped pulse amplification technology, and encounter amplified nanosecond (ns), picosecond, or femtosecond laser pulse irradiation. Damage behavior in the ns regime is statistically significant; however, only the 1-on-1 test method was employed in previous studies to identify the damage precursors. Here, we adopted a raster scan procedure with mass test samplings to comprehensively evaluate the damage characteristics of MLDGs. The damage experiment was conducted at 1064 nm with a pulse width of 8 ns. The laser-induced damage thresholds (LIDTs) for the MLDGs were shown to be approximately 30% lower than those of multilayer dielectric films (MLDFs). The normalized electric field intensity |E |2 (EFI) enhancement caused by the surface-relief grating structure and incomplete grating cleaning contributed to this LIDT reduction. Three discrete damage-initiation morphologies near the LIDT were found: nodular ejection, nano absorbing defect damage, and plasma scalding. In addition to the nodular defect damage that usually occurs in the fundamental frequency high reflectors, the strong absorption of nano defects and the poor interfacial quality make the interface nano absorbing defects of the MLDG also easily triggered. The interface differences between the MLDG and MLDF should be related to multiple annealing processes during MLDG fabrication. The plasma scalding behaves as a color change and is only involved at the surface of the grating pillar. The slight dependence of damage morphology on the EFI peak was first observed.