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15 January 2007 Mitigation of laser damage on fused silica surfaces with a variable profile CO2 laser beam
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Laser damage at 3ω, 351 nm, of fused silica optical components is a major concern for LMJ maintenance. Indeed, even a low density of damage sites is unacceptable due to the exponential growth of surface damage with a series of laser shots. A technique is now used to prevent the growth of initiated damage sites : this mitigation technique consists in a local melting and evaporation of silica by CO2 laser irradiation on the damage site. Even if the growth is stopped in most cases, we showed previously that some of the mitigated sites re-initiate on their peripheral area, where most of redeposited debris are located. To further increase the efficiency of mitigation technique, the treatment was improved by varying the spatial profile of the CO2 laser beam. We present here the new set-up and the results obtained in terms of laser damage resistance: about 98% of the mitigated sites sustained 200 shots of a 10 J/cm2 3ω YAG laser without damage.
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Annelise During, Philippe Bouchut, Jean-Guillaume Coutard, Christophe Leymarie, and Hervé Bercegol "Mitigation of laser damage on fused silica surfaces with a variable profile CO2 laser beam", Proc. SPIE 6403, Laser-Induced Damage in Optical Materials: 2006, 640323 (15 January 2007);

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