Researchers from the Shanghai Institute of Optics and Fine Mechanics (SIOM) of the Chinese Academy of Sciences (CAS), Wuhan University of Technology, University of Science and Technology of China of CAS and Research Center of Laser Fusion of the China Academy of Engineering Physics, analyzed the dynamic process of multi-pillars continuous damage of the pulse compression grating under picosecond laser irradiation, and found the direction for improving the picosecond laser damage resistance of pulse compression grating. The study was published in High Power Laser Science and Engineering. 

Laser-induced damage of pulse compression gratings is the bottleneck for restricting the output capacity of the laser system. Determining the laser damage dynamic process of grating components is the main way to clarify the damage mechanism and to improve the damage threshold. 

The researchers extracted and correlated the typical damage morphologies of the pulse compression grating after a single picosecond-pulsed laser irradiation. Through theoretical simulation, they confirmed the process of multi-pillars continuous damage. The laser electric field enhancement in the grating relief and the shallow defects on its surface together triggered the local eruption of the grating material. Afterwards, the impact pressure of the ejected materials caused the adjacent pillars to fracture.

The simulation results showed that the eruptive pressure, generated by the local ionized material of the grating resulted in a stress concentration at the root of the adjacent pillar, was sufficient to cause damage, corresponding to its damage characteristics in the experiment. The picosecond laser damage process of the grating is affected by shallow defects, strong electric field and strength of the grating pillars. 

This study provides a direction for improving the picosecond laser damage resistance of pulse compression grating.  

Schematic representation of the picosecond laser-induced damage process of multilayer dielectric grating. (Image by SIOM)