Threshold fluences for conditioning, fatigue and damage effects of DKDP crystals

Abstract

Conditioning, fatigue and damage characteristics on the surface of DKDP nonlinear optical crystals were studied under the irradiation of 1064 nm (1ω) and 355 nm (3ω) lasers. Conditioning takes effect as laser fluence reaches the lower limit of conditioning, 6∼8 J/cm2 and 4∼6 J/cm2 for 1064 nm and 355 nm in our experiments, respectively; further increase in laser fluence will induce fatigue effects when fluence exceeds the “safe” fluence, ∼10 J/cm2 and ∼8 J/cm2 for 1064 nm and 355 nm laser light in the experiments; 1-on-1 damage will take place if fluence is sufficiently high, > 17 J/cm2 (1064 nm) and 11 J/cm2 (355 nm) in our cases. In the conditioning regime, greater fluence will result in more damage-resistant DKDP surface and increasing the number of conditioning laser pulses will have similar influence on damage resistance of DKDP surface. When the laser fluence falls into the band of fatigue effects, the laser induced damage threshold (LIDT) drops with increasing pulse number of conditioning laser incident on DKDP surface and finally stabilizes at a certain value, “safe” fluence, below which DKDP surface cannot be damaged macroscopically even if a myriad of laser pulses shoot the DKDP surface. The “safe” fluence is usually 60%∼80% of 1-on-1 LIDT. Our work will be beneficial to optimization of laser conditioning and to provide insights into laser-induced damage in DKDP crystals.