High Damage Resistivity of Optical Surface for UV Lasers by Ion Beam Etching

Effect of ion beam etching on laser-induced surface damage was investigated in CsLiB6O10 (CLBO) crystaland fused silica. In high-power UV lasers, these optical surfaces were damaged due to absorption of thepolishing compound embedded inside the surface. From SIMS analysis, the polishing compounds were foundto be embedded in the CLBO and fused silica surfaces to a depth of 60 nm. These polishing compounds couldbe removed by using Ar ion beam etching. No ion beam-induced surface damage was observed when theapplied ion beam voltage was less than 200 V. Due to the effect of polishing compounds removal on damageresistivity, the laser-induced surface damage threshold of CLBO was improved up to 16 J/cm2 (wavelength: 355 nm, pulse width: 0.85 ns) as compared with that of the as-polished surface 11 J/cm2. The laser-inducedsurface damage of fused silica also increased from 7.5 J/cm2 to 14.5 J/cm2.