# Low-pressure plasma cleaning of organic contamination from chemically coated surfaces: a study combining experimental and molecular dynamics studies

## TL;DR

This study explores how low-pressure plasma can clean organic contaminants from optical coatings, combining experiments and simulations to improve cleaning efficiency.

## Contribution

The paper introduces a combined experimental and molecular dynamics approach to understand and optimize low-pressure plasma cleaning of organic contaminants.

## Key findings

- Low-pressure oxygen plasma effectively removes organic films from coated optics.
- Molecular dynamics simulations reveal the microscopic mechanisms of plasma cleaning.
- Optical performance can be restored to near-baseline levels using optimized plasma parameters.

## Abstract

During prolonged service in vacuum-based intense laser systems, the surface chemical coatings of large-aperture optical components inevitably suffer from organic contamination, leading to irreversible damage to the surface chemical coatings and a rapid degradation of the optical performance under laser irradiation. This study uses experiments and simulations to examine the process and microscopic mechanisms associated with the removal of organic contaminants from surface chemical coatings through low-pressure plasma cleaning. Firstly, a capacitive-coupling discharge model for the low-pressure plasma cleaning device was constructed through finite element simulations to obtain the spatial distribution of plasma discharge characteristics. Langmuir probe and emission spectrometer experiments were conducted to explore the plasma discharge laws and determine the effects of the plasma parameters on the discharge characteristics and the types of reactive particles excited in low-pressure plasma of oxygen and argon gas. Secondly, a quantitative relationship between the number of typical functional groups in organic contaminants and the transmittance of optical components was established. Various low-pressure plasma cleaning experiments were performed by adjusting the core plasma parameters to analyze the effects of these parameters on the cleaning performance. Finally, based on the reactive force field, a molecular dynamics model of the interaction between the plasma and organic contaminants was constructed. Simulation results revealed the reaction mechanisms between the plasma and organic contaminants, which provided a theoretical explanation of the microscopic mechanism of plasma cleaning. The results of this study offer theoretical guidance and practical verification from the microscopic mechanism and macroscopic practical perspective for the efficiency improvement of the plasma cleaning technology for organic contaminants.

Low-pressure oxygen plasma removes realistic organic films from coated optics via radical-driven pathways. Probe/Raman spectroscopy and reactive MD converge on process windows that restore near-baseline optical performance.