Laser induced fluorescence as a tool for the study of laser damage precursors in transparent materials

Potassium dihydrogen phosphate (KH2PO4 or short KDP) is one of the major nonlinear optical crystals for frequency conversion and electro-optic switching in high power lasers. In particular, this material has been chosen for the frequency converters of the Laser Mega Joule in France and the National Ignition Facility in the US. These laser work close to the damage threshold of the crystals and large efforts have been provided to improve the laser induced damage threshold for KDP at different wavelength. We present in this paper first results of a new setup dedicated to the correlation of non destructive luminescence spectroscopy and destructive laser damage tests. We concentrate on the differences between conventionally grown KDP and KDP-crystals that have been produced by the rapid growth method that has been developed in the last years especially for the large laser installations LMJ and NIF. Different photoluminescence spectra are obtained from conventionally and rapidly grown KDP for both pump configurations: (i) pulsed pumping by the forth harmonic of a Nd:YAG laser at 266nm, and (ii) continuous pumping using a frequency doubled Argon ion laser at 244nm.