Observation of nanosecond laser-induced phase explosion in aluminum

The transition from normal vaporization to phase explosion during laser ablation of aluminum was investigated using a nanosecond Nd:YAG laser. The threshold nature of phase explosion was observed by a discontinuous jump in the ablation depth at approximately 5.2J∕cm2. Ablation was imaged using a shadowgraph technique that was capable of probing ablation with nanosecond exposure time and nanosecond time delay resolution with respect to laser heating. Images above the threshold captured a mixture of vapor and droplets generated by phase explosion, which began near the end of the laser pulse without a significant time lag.