Self-laser conditioning of KDP and DKDP crystals

We have laser conditioned a couple of KDP-SHG and DKDP-THG samples thanks to a facility which delivers 6 ns fundamental (1,053 nm, noted 1 omega) pulses, and the harmonics generated by the crystals themselves. The conditioning ramp has been established according to a model coupling statistics and heat transfer, in order to minimize the generation of bulk laser damage during the process. Then the efficiency of this procedure has been evaluated for both samples using two laser damage testing setups, and compared to the best monochromatic conditioning process known to date. For the KDP-SHG, it appears that this procedure is less efficient than the monochromatic conditioning. But it raises the resistance to laser damage of the SHG to a level compatible with the use on Megajoule-class high power lasers. For the DKDP-THG, the efficiency of both procedures is quite similar. And even if the conditioned THG still exhibits laser damage within the range of high power laser working fluences at 351 nm, the density is only a few per mm3. (authors)