Energetic laser cleaning of metallic particles and surface damage on silica optics: investigation of the underlying mechanisms

Nan Shen; Stavros G. Demos; Raluca A. Negres; Alexander M. Rubenchik; Candace D. Harris; Manyalibo J. Matthews

doi:10.1117/12.2195593

23 November 2015 Energetic laser cleaning of metallic particles and surface damage on silica optics: investigation of the underlying mechanisms

Nan Shen, Stavros G. Demos, Raluca A. Negres, Alexander M. Rubenchik, Candace D. Harris, Manyalibo J. Matthews

Author Affiliations +

Proceedings Volume 9632, Laser-Induced Damage in Optical Materials: 2015; 96320V (2015) https://doi.org/10.1117/12.2195593
Event: SPIE Laser Damage, 2015, Boulder, Colorado, United States

Abstract

Surface particulate contamination on optics can lead to laser-induced damage hence limit the performance of high power laser system. In this work we focus on understanding the fundamental mechanisms that lead to damage initiation by metal contaminants. Using time resolved microscopy and plasma spectroscopy, we studied the dynamic process of ejecting ~30 μm stainless steel particles from the exit surface of fused silica substrate irradiated with 1064 nm, 10 ns and 355 nm, 8 ns laser pulses. Time-resolved plasma emission spectroscopy was used to characterize the energy coupling and temperature rise associated with single, 10-ns pulsed laser ablation of metallic particles bound to transparent substrates. Plasma associated with Fe(I) emission lines originating from steel microspheres was observe to cool from <24,000 K to ~15,000 K over ~220 ns as τ^-0.22, consistent with radiative losses and adiabatic gas expansion of a relatively free plasma. Simultaneous emission lines from Si(II) associated with the plasma etching of the SiO₂ substrate were observed yielding higher plasma temperatures, ~35,000 K, relative to the Fe(I) plasma. The difference in species temperatures is consistent with plasma confinement at the microsphere-substrate interface as the particle is ejected, and is directly visualized using pump-probe shadowgraphy as a function of pulsed laser energy.

Citation Download Citation

Nan Shen, Stavros G. Demos, Raluca A. Negres, Alexander M. Rubenchik, Candace D. Harris, and Manyalibo J. Matthews "Energetic laser cleaning of metallic particles and surface damage on silica optics: investigation of the underlying mechanisms", Proc. SPIE 9632, Laser-Induced Damage in Optical Materials: 2015, 96320V (23 November 2015); https://doi.org/10.1117/12.2195593

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