Enhanced ablation and photoacoustic excitation in near-threshold laser ablation of liquid-coated surfaces

Abstract

The effect of an artificially deposited liquid film on a laser-ablated metal surface at near-threshold laser fluences is presented. Experiments utilizing a Q-switched Nd:YAG laser (wavelength=1064 nm, full width at half maximum=6 ns) reveal that deposition of a liquid film results in substantial reduction of ablation threshold and enhancement of ablation yield. In addition, enlarged photoacoustic emission is detected in the ablation involving the liquid film. The augmentation of ablation efficiency at high laser fluences is known to be induced by confinement of laser-generated plasma in the liquid layer. In contrast, the enhancement in the near-threshold regime, as in the present study, is primarily due to the photomechanical effect associate with the explosive liquid vaporization in the strongly superheated liquid layer. The effect of liquid-film thickness on near-threshold ablation are also examined for two different liquids, water and water/isopropanol mixture. (C) 2001 American Institute of Physics.