Nd:YAG laser conditioning of KDP crystals investigated using nondestructive optical diagnostics

Abstract

Potassium Dihydrogen Phosphate (KDP) is a non-linear optical material for the Pockelscells and laser frequency conversion used in inertial confinement fusion (ICF).But the performances are decreased by the presence of defects or impurities from the growth process. Furthermore, it is difficult to identify them due to their small size and sparse distribution. Laser conditioning provides an increase for the material damage resistance due to an unknown physical mechanism resulting from the interaction of sub-damage laser pulses with KDP defects. In this paper, the crystals first were laser conditioned by raster scanning using Nd:YAG laser at 355nm with pulse durations of approximately 7 ns. Then we investigated the KDP crystals with different non-destructive optical diagnostics. We measured in the same time the fluorescence, the photothermal absorption, Raman and FTIR spectroscopy of the material. We concentrated on the differences of conventionally grown KDP crystals before and after the laser conditioning. We obtained the different spectra information of KDP crystals.