Surface damage and radiation resistance of lithium tetraborate single crystals

The surface damage thresholds of Li₂B₄O₇ crystals, nonlinear crystals used in ultraviolet (UV) solid-state lasers, were measured and found to be 8.4 GW/cm² at 1064 nm, 1.9 GW/cm² at 532 nm, and 0.83 GW/cm² at 266 nm. The damage threshold at 1064 nm was 1.5 times higher than that of fused silica. In addition, the direction dependence of the damage threshold was {1 1 0}>{0 0 1}>{1 0 0}. No color center was generated in the crystal after 20 W/cm², 10⁷ shots irradiation of KrF and ArF excimer lasers. The excellent damage threshold and radiation resistance of Li₂B₄O₇ were attributable to its wide band gap and relatively few defects in the crystal.