Carrier dynamics in KDP and DKDP crystals illuminated by intense femtosecond laser pulses

The dynamics of electrons and holes in potassium dihydrogen phosphate (KH2PO4 or KDP) crystals and its deuterated analog (KD2PO4 or DKDP) induced by femtosecond laser pulses is investigated at lambda = 800nm. To do so, experiments based on a femtosecond time-resolved interferometry technique have been carried out. It is shown that two relaxation dynamics exist in KDP and DKDP crystals. In particular, it appears that one dynamics is associated with the migration of proton/deuteron in the crystalline lattice. Both of the dynamics correspond to physical mechanisms for which the multiphoton order required to promote valence electrons to the conduction band is lower than the one of a defect-free crystal. These results suggest the presence of states located in the band gap that may be due to the presence of defects existing before any laser illumination or created in the course of interaction. In order to interpret the experiments, a model based on a system of rate equations has been developed. Modeling results are in good agreement with the experimental data, and allow one to obtain fundamental physical parameters governing the laser-matter interaction as multiphoton absorption cross sections, capture cross sections, recombination times, and so forth. Finally, it will be shown how these results can be used to the understanding of laser-induced damage by nanosecond pulses in inertial confinement fusion class laser aperture.