Abstract
The laser-induced damage threshold of optics is an issue of essential importance in high-power laser applications. However, the complex and partially interacting mechanisms as well as the underlying reasons for laser damage of glass surfaces are not yet fully understood. The aim of the present work is to contribute to a better understanding of such damage mechanisms by providing original results on the impact of classical glass surface machining on the laser-induced damage threshold. For this purpose, glass samples were prepared with well-defined process conditions in terms of the used lapping and polishing agents and suspensions. Further, the samples were post-processed by atmospheric pressure plasma for precision cleaning. The laser-induced damage threshold and surface contamination by residues from the manufacturing process were determined before and after plasma post-processing. It is shown that the polishing suspension concentration has a certain impact on the laser-induced damage threshold and surface contamination by residues from used working materials. The highest damage threshold of 15.2 J/cm² is found for the lowest surface contamination by carbon which occurs in the case of the highest polishing suspension concentration. After plasma treatment for merely 60 s, this value was increased to 20.3 J/cm² due to the removal of surface-adherent carbon. The results thus imply that the laser-induced damage threshold can notably be increased by first choosing appropriate process parameters during classical manufacturing and second plasma post-processing for surface finishing.
Highlights
Optical components with high laser-induced damage threshold (LIDT) are of essential importance for the realisation of optical systems used for high-power laser setups and facilities
The results presented in this work clearly show that the laser-induced damage threshold of the investigated glass is directly related to surface contamination by carbon
The highest LIDT was found for the lowest contamination which occurred in the case of the highest polishing suspension concentration
Summary
Optical components with high laser-induced damage threshold (LIDT) are of essential importance for the realisation of optical systems used for high-power laser setups and facilities. Conventional optical manufacturing involves rough grinding, fine grinding or lapping, and polishing By these steps, material removal is achieved by the application of different abrasives where the mechanical impact of such abrasives on the glass surface comes along with the formation of either open or closed subsurface. The crack depth is approximately 0.3 times the mean diameter of the used abrasive grains and ranges from 1 to 20 μm for polished surfaces [1] Such cracks were identified to play a key role for laser damage due to the formation of interference effects, an increased absorption and a reduction in mechanical strength of a glass surface [2,3]. This leads to a complex possible contamination consisting of (i) mineral oil-containing cooling lubricants used during rough grinding, (ii) wear debris from abrasive grains, e.g., silicon carbide (SiC) or diamond (C)
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