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 {110}>{001}>{100}. 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 crytal.