A model of laser-induced damage of KDP based on the coupling of statistics and heat transfer

By coupling statistics and heat transfer, we investigate numerically laser-induced KDP crystal damage by multi-gigawatt nanosecond pulses. Our model is based on the heating of nanometric absorbing defects that may cooperate when they are sufficiently aggregated. In such a case, they induce locally a strong increase of temperature that may lead to a subsequent damage. Statistics is used to evaluate the initial defect cluster size distribution. When the crystal is illuminated, by considering in addition heat transfer processes, this approach allows to predict damage probabilities and the evolution of the damaged sites density as a function of the laser fluence. We show that the scaling law exponent, linking the critical laser fluence to its pulse duration, takes a value close to 0.3 departing from the standard 0.5 value that is in a good agreement with recents experiments. Furthermore, these results indicate that absorbers involved in KDP damage may be associated with a collection of planar defects.