Damage to Fused-Silica, Spatial-Filter Lenses on the OMEGA Laser System
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چکیده
114 LLE Review, Volume 78 Vacuum surface damage to fused-silica, spatial-filter lenses is the most prevalent laser-damage problem occurring on the OMEGA laser system. Approximately one-half of the stage-Cinput and output, D-input, E-input, and F-input spatial-filter lenses are currently damaged with millimeter-scale fracture sites. With the establishment of safe operational damage criteria, laser operation has not been impeded. These sol-gel-coated lenses see an average fluence of 2 to 4 J/cm2 (peak fluence of 4 to 7 J/cm2) at 1053 nm/1 ns. Sol-gel coatings on fused-silica glass have small-spot damage thresholds at least a factor of 2 higher than this peak operational fluence. It is now known that the vacuum surfaces of OMEGA’s spatial-filter lenses are contaminated with vacuum pump oils and machine oils used in the manufacture of the spatial-filter tubes; however, development-phase damage tests were conducted on uncontaminated witness samples. Possible explanations for the damage include absorbing defects originating from ablated pinhole material, contamination nucleated at surface defects on the coating, or subsurface defects from the polishing process. The damage does not correlate with hot spots in the beam, and the possibilDamage to Fused-Silica, Spatial-Filter Lenses on the OMEGA Laser System
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