Origin of near-ultraviolet absorption of nonlinear BBO crystals

Defects in nonlinear optical barium metaborate crystals have been investigated by means of optical spectroscopy and thermally activational methods. Low-temperature absorption peaks have been observed at all samples. The dependence of these peaks upon crystalline phase and type of the flux used while growing is low. This fact indicates that intrinsic defects play the leading role in absorption origination. It is shown that while growing BBO crystals by TSSG technique, defects, which form deep electron-type traps in the forbidden gap, are generated.