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

Abstract

ABSTRACT The dynamics of electrons and holes in potassium dihydrogen phosphate (KH 2 PO 4 or KDP) crystals and itsdeuterated analog (KD 2 PO 4 or DKDP) induced by femtosecond laser pulses is investigated at = 800 nm .Todo so, experiments based on a femtos econd time-resolved interferometr y technique have been carried out. Itis shown that two relaxation dynamics exist in KDP and DKDP crystals. In particular, it appears that onedynamics is associated with the migration of proton/deuteron in the crystalline lattice. Both of the dynamicscorrespond to physical mechanisms for which the multi photon order required to pr omote valence electrons tothe conduction band is lower than the one of a defect-free crystal. These results suggest the presence of stateslocated in the band gap that may be due to the presence of defects existing before any laser illumination orcreated in the course of inte raction. In order to interpr et the experiments, a model based on a system of rateequations has been developed. Modeling results are in good agreement with the experimental data, and allowone to obtain fundamental physical parameters governing t he laser-matter interaction as multiphoton absorptioncross sections, capture cross sectio ns, recombination times, and so forth. Finally, it will be shown how theseresults can be used to the understanding of laser-induced damage by nanosecond pulses in inertial con“nementfusion class laser aperture.Keywords: Interferometry, femtosecond laser, KDP crystal, laser damage, modeling, rate equations