Effect of multiple wavelengths on laser-induced damage in KH(2-x)DxPO4 crystals

Laser-induced damage is a key factor that constrains the ways in which optical materials are used in high-power laser systems. We study the size and density of bulk laser-induced damage sites formed during frequency tripling in a DKDP crystal. The characteristics of the damage sites formed during tripling, for which 1053, 526, and 351 nm light is simultaneously present, are compared to those of damage sites formed by 351 nm light alone. The fluence of each wavelength is calculated as a function of depth with a full 4D(x,y,z,t) frequency conversion code and compared with measured damage density and size distributions. The density of damage is found to be governed predominantly by 351 nm light with some lesser, though nonnegligible, contribution from 526 nm light. The 1053 nm light does not appear to contribute to the damage density. The morphology of the damage sites, however, is seen to be relatively insensitive to wavelength and to depend only on total fluence of all wavelengths present. The strong and negligible wavelength dependences of initiation density and damage morphology, respectively, indicate that the dominant energy deposition mechanism varies during the damaging pulse.