Pump-pump experiment in KH2PO4 crystals: Coupling two different wavelengths to identify the laser-induced damage mechanisms in the nanosecond regime

Laser-induced damage experiments based on an original pump-pump set-up have been carried out in the nanosecond regime for KH2PO4 (KDP) crystal. The impact of a simultaneous mixing of 351 nm and 1064 nm pulses has been experimentally studied and compared to a model based on heat transfer, the Mie theory and a Drude model. This study sheds light on the physical processes implied in the KDP laser damage. In particular, a three-photon ionization mechanism is shown to be responsible for laser damage in KDP.