Optical near-field ablation-induced plasma characteristics

The physics of optical near-field based laser ablation plasmas is studied. A Cr thin metal film is ablated using visible nanosecond laser pulses coupled through an optical near-field fiber probe. The ablated plasma evolution is monitored via time-resolved emission imaging and spectral measurement. Intense plasma formed in the proximity of the near-field gap within the laser pulse duration and decayed after several nanoseconds. Highly directional jetlike material ejection was observed at later time scales. The measured spectra reveal that early stage plasma of short lifetime yields ablated material characteristic emission peaks, supporting possible application to laser-induced breakdown spectroscopy.