Laser irradiation effects on gold

Abstract

Investigations on the laser irradiation effects on gold are explored in terms of plasma-plume dynamics and morphological and crystallographic changes. Annealed 4N gold samples were irradiated with a Q-switched Nd:YAG laser (53 mJ, 21 MW, 532 nm, and pulse width 6–8 ns) for plume dynamics using 10-ns gated fast photography. A Q-switched pulsed Nd:YAG laser (10 mJ, 1.1 MW, 1064 nm, and pulse width 9 ns) was used to irradiate the surface of the samples for morphological and crystallographic studies of laser-irradiated gold in a vacuum ∼10−3 Torr. The annealed samples were exposed to 50 shots of a Nd:YAG laser (10 mJ, 1.1 MW, 1064 nm, and pulse width 9 ns). The investigation on the plume was done by using an intensified charged-couple device ICCD-5760/IR-UV camera. The morphological investigation of the irradiated surface was carried out by analyzing micrographs obtained using an Hitachi S 3000 H scanning-electron microscope (SEM). The crystallographic studies of the irradiated samples were performed by analyzing the XRD patterns obtained using an X’ Pert Pro Pan Analytical X-ray diffractometer. The investigation on gated ICCD images of the plume reveal that, at very earlier times, the plasma-plume expansion has a linear trend, whereas, at later times, the plasma-plume expansion is nonuniform. SEM micrographs exhibit the primary mechanisms of pulsed-laser ablation (PLA), such as hydrodynamic sputtering, thermal sputtering, exfoliation sputtering, and splashing. The surface morphology was explained in terms of crater formation, swelling, burning, nucleation, grain growth, and nonsymmetric heat conduction. The nonuniform thermal expansion of gold due to thermal-energy transfer is also studied by SEM micrographs, which was supported by XRD analysis. The structural analysis on the basis of XRD shows that the composition of the irradiated samples is not disturbed even after laser irradiation. The grain sizes also changed due to laser irradiation.