Microscopic chemical reaction mechanism of carbon contaminants on the surface of pulse-compressed gratings cleaned by low-pressure plasma

Abstract

Removing carbon contaminants from the surfaces of pulse-compressed gratings is a critical aspect of maintaining the functionality and efficiency of a chirped pulse amplification system. In this study, a method of in situ cleaning pulse-compressed gratings by low-pressure plasma is proposed and delves into the microscopic chemical reaction mechanism involved in eliminating carbon contaminants. Firstly, the surface contamination state and formation mechanism of the grating were analyzed, and the influence of the contaminants on the morphology and diffraction efficiency was discussed. The diffraction efficiency of the grating post-contamination can decrease by one-third. After a 5.5 hour low-pressure air plasma cleaning, carbon contaminants on the grating surface were completely removed, restoring both the diffraction efficiency and the surface morphology of the grating. Reactive molecular dynamics simulations were executed to model the intricate reaction mechanisms of eliminating carbon contaminants using low-pressure plasma. The cleaning efficiency, particularly on pulse-compressed gratings, was studied under low-pressure plasma conditions to elucidate the underlying mechanisms responsible for carbon contaminant removal. The research revealed a detailed pathway of chemical reactions initiated by the interaction of carbon contaminants with the plasma cleaning. Notably, the study identified key stages in the process, including the breakdown of carbon chains, the formation of new chemical bonds, and the evolution of molecular structures on the grating surface. Insights gained from this study provide valuable information for optimizing plasma cleaning processes tailored to pulse-compressed gratings, paving the way for improved maintenance strategies in optical applications.