Laser-induced damage in nonlinear crystals on irradiation direction and polarization

Nonlinear-optical crystals are attractive materials for the high-power frequency converter with high damage threshold, phase matching characteristics, wide transparency range, and large effective nonlinear coefficients. Especially as to the power laser applications, its laser-induced damage threshold determines the limit of performance in the optical system. The threshold depends not only on the intrinsic material parameters but also on the laser beam parameters is use. We have investigated the bulk damage threshold of several crystals at a single-shot operation for frequency converter depending on the laser irradiation direction and its polarization. For KDP and CLBO crystals, the damage threshold in the direction of c-axis is about tow times higher than that in the a- or b-axis at 1.064 micrometers of wavelength. This result is consistent with the molecular bonding structure in different directions of the crystal. The relation between the bulk damage pattern and the crystal structure is also discussed.