15 January 2007 Mitigation of growth of laser initiated surface damage in fused silica using a 4.6-micron wavelength laser
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Abstract
Surface damage caused by high fluence, 351 nm light to fused silica optics can adversely affect the performance of fusion class laser systems like that of the National Ignition Facility (NIF). It is typically initiated as a small pit and grows in both diameter and depth during normal operation with cracks that extend into the bulk. Mitigation of this growth has been previously reported using a 10.6 micron CO2 laser. Here, we report growth mitigation with the 4.6 micron light from a frequency-doubled, 9.2 micron CO2 laser. The motivation for using 4.6 microns is >25 times longer absorption length in fused silica at room temperature compared to that at 10.6 micron. Mitigation of subsurface cracks at 10.6 micron required ablation of material to the depth of the cracks. In contrast, it was possible to mitigate the subsurface cracks using 4.6 micron light without significant ablation of material. Damage sites as large as 500 microns in diameter with cracks extending to 200 microns in depth were successfully mitigated with 4.6 microns.
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Gabe Guss, Isaac Bass, Vaughn Draggoo, Richard Hackel, Steve Payne, Mark Lancaster, Paul Mak, "Mitigation of growth of laser initiated surface damage in fused silica using a 4.6-micron wavelength laser", Proc. SPIE 6403, Laser-Induced Damage in Optical Materials: 2006, 64030M (15 January 2007); doi: 10.1117/12.696084; https://doi.org/10.1117/12.696084
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