Modeling of laser-induced damage in KDP crystals by nanosecond pulses: a preliminary hydrodynamic study

The aim of this preliminary study is to provide a simple model for estimating the laser-induced damage formation in potassium dihydrogen phosphate crystals (KH2PO4 or KDP) irradiated by nanosecond laser pulses operating at 351nm. In our modelling approach, a damaged site is assumed to be induced from a nanometric existing defect, i.e. a precursor defect. It makes it possible to absorb an important part of the incident laser energy which results in a damage formation by some processes which combine heating and hydrodynamic processes. In our model, the main expected features of the damage scenario are accounted for: the defect-assisted laser absorption and subsequent plasma formation and evolution, the plasma absorption, heat transfer and hydrodynamic processes via a simple Equation Of State (EOS). In these calculations, a crystal zone is assumed to damage since it undergoes high enough density variations. Calculations shows that a nanometric precursor defect can effectively lead to damaged site of several tens of micrometers in size as observed experimentally. Also, we demonstrate the reliability of the long-standing assumption regarding the precursor defect size. Furthermore, a particular morphology of the damaged site exhibiting various regions is obtained. These estimates have now to be confirmed especially by improving the EOS and by introducing an elasto-plastic behavior.