Distribution of defects induced in fused silica by ultraviolet laser pulses before and after treatment with a CO2 laser

The depth distribution of ultraviolet laser irradiation-induced defects in fused silica has been determined using cathodoluminescence (CL) microanalysis. CL emissions have been observed at 1.9, 2.2, 2.7, and 4.4 eV. In addition, following a CO2 laser treatment for damage mitigation, an emission at 3.2 eV is also observed. The CL emissions have been identified with the nonbridging oxygen hole center, the self-trapped exciton, the oxygen-deficient center, and the aluminum impurity center. The spatially resolved CL data are consistent with the damage initiation at the exit surface. The concentration of 355-nm laser-induced defects is greatest at the surface and monotonically decays to preirradiation levels at ∼10-μm depth below the surface. The CO2 processing reduces the defect concentration and spatial distribution to a maximum depth of ∼6μm, confirming significant damage mitigation.