Toward a Better Understanding of Multi-Wavelength Effects on KDP Crystals

Laser damage in KDP crystals has been studied since several years and more accurately with emergence of projects like LMJ (Laser MegaJoule, in France) or NIF (National Ignition Facility, in US). Laser damage tests are essentially performed at 351-nm wavelength (3 omega), with regards to their optical behaviours on forementioned facilities. But only few data are available at 1064 nm (1 omega) and at 532 nm (2 omega), and even with wavelength-mixing more representative of operational conditions of KDP crystals. So in a first approach, we tried to carry out an identity chart of the crystal by performing mono-wavelength tests at 1 omega, 2 omega and 3 omega Then, a campaign of combination of multi-wavelength (typically 3 omega and 1 omega) tests has been started with several temporal delays between 3 omega and 1 omega pulses. These first results lead us to improve pre-existing modelling codes developed by CEA, which have proved their robustness to 3 omega-experiment results. Foremost interests consist in implementing wavelength dependency and energy deposition mechanism as a consequence of our first observations on KDP.