MRF, ELSM and STED: tools to study defects in fused silica optics

R. Catrin; D. Taroux; P. Cormont; C. Maunier; J. Neauport

doi:10.1117/12.2030420

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14 November 2013 MRF, ELSM and STED: tools to study defects in fused silica optics

R. Catrin, D. Taroux, P. Cormont, C. Maunier, J. Neauport

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Proceedings Volume 8885, Laser-Induced Damage in Optical Materials: 2013; 88852D (2013) https://doi.org/10.1117/12.2030420
Event: SPIE Laser Damage, 2013, Boulder, Colorado, United States

Abstract

The MegaJoule laser being constructed at the CEA near Bordeaux (France) is designed to focus more than 1 MJ of energy at 351 nm, on a millimetre scale target in the centre of an experiment chamber. The final optic assembly of this system operating at a wavelength of 351 nm is made up of large fused silica optics, working in transmission, that are used to convey and focus the laser beam. Under high fluences (i.e. more than 5 J/cm² for 3 ns pulses), the limited lifetime of final optical assembly is a major concern for fusion scale laser facilities. Previous works have shown that surface finishing processes applied to manufacture these optical components can leave subsurface cracks (SSD), pollution or similar defects that act as initiators of the laser damage. In this work, we used epi-fluorescent light scanning microscopy (ELSM) and Stimulated Emission Depletion (STED) in confocal mode with fluorescent dye tagging to get a better knowledge of size and depth of these subsurface cracks. Magnetorheological fluid finishing technique (MRF) was also used as a tool to remove these cracks and thus assess depths measured by confocal microscopy. Subsurface cracks with a width of about 120 nm are observed up to ten micrometers below the surface.

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R. Catrin, D. Taroux, P. Cormont, C. Maunier, and J. Neauport "MRF, ELSM and STED: tools to study defects in fused silica optics", Proc. SPIE 8885, Laser-Induced Damage in Optical Materials: 2013, 88852D (14 November 2013); https://doi.org/10.1117/12.2030420

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