Laser damage to production- and research-grade KDP crystals

Abstract
We present the results of laser damage measurements conducted on potassium dihydrogen phosphate (KDP) and deuterated potassium dihydrogen phosphate (KD*P) crystals that were grown recently for both production and research applications by several sources. We have measured extrinsic damage thresholds that cover wavelengths from 1064 nm to 266 nm at pulse durations in the 3 to 10 ns regime. Many of the samples were extracted from boules grown specifically to yield large-area crystals, up to 32 cm square, for laser fusion applications. These crystals were the result of efforts, both by the Lawrence Livermore National Laboratory (LLNL) and commercial crystal-growth companies, to yield high- threshold KDP. In particular we have established that such crystals can reliably survive fluences exceeding 15 J/cm2 at 355 nm and 20 J/cm2 at 1064 nm when irradiated with 3 ns pulses. We present details of how bulk and surface damage to these crystals scale with pulse duration and wavelength as well as of morphological effects due to laser conditioning.