Extended measurement of crater depths for aluminum and copper at high irradiances by nanosecond visible laser pulses

The effects of high power laser on aluminum and copper targets are investigated experimentally. Shadowgraph imagining is used to observe the expulsion of the material, plasma-plume formation and shock wave generation. Confocal microscopy is used for crater depth analysis, which showed that two distinctive regimes exist. At irradiances lower than 1011 W/cm2 the crater depth increases monotonically with the increase of irradiation. At higher irradiances, crater depth of aluminum reaches a limit value while in the case of copper, the crater depth decreases between 1011 and 2 × 1012 W/cm2, and then increases again. The present results clarify the effect of plasma shielding on limiting crater depths by providing first time measurements for metals at high irradiance regime.