Observation of a transient insulating phase of metals and semiconductors during short-pulse laser ablation

We have investigated the dynamics of femtosecond laser-induced ablation from the surface of various materials. Combining pump–probe techniques with optical microscopy we have monitored the structural modifications of the irradiated surfaces both in space and time. In the fluence regime below the threshold for plasma formation ablation is caused by the hydrodynamic expansion of laser-heated material. Upon expansion into vacuum each of the investigated materials Si, GaAs, Al, Au, Mg, Hg. evolves from the initial metallic state into an optically transparent phase with high index of refraction. q1998 Elsevier Science B.V.