Influence of initial micro-porosity of target on material ejection under nanosecond laser pulses

Heating and explosive destruction of the near surface volume of metal with initial micro-porosity under nanosecond laser pulse is simulated. It is shown that presence of initial micro-porosity may influence and modify the ejection mechanisms from melt and from solid phase. Thermal and gas dynamic processes in a gas bubble growing in laser irradiated melt are analysed. Experiments show rather different surface morphology defined by micro-explosions and melt ejection for different metals. Possible explosion of micro-pores and solid particles release under nanosecond laser irradiation is analysed for metals with high melting point. It is shown that the stress attains the values that are close to the damage threshold.