UC Berkeley

Time-resolved emission and scattering imaging are employed to analyze the ablation mechanisms of silver thin films induced by femtosecond laser irradiation of Gaussian intensity profile under different laser fluences and gas background pressures. At fluences near the ablation threshold, nanoparticles (NPs) of 40 nm–100 nm in size are ejected in the vertical direction from the target sample. The average ejection speed of these NPs increases with the laser fluence and also as the background gas pressure drops from ambient atmospheric to ∼10−5 Torr. At higher fluences, a plume is formed at the center of the laser beam and NPs are released in oblique trajectories from the peripheral area of the laser-irradiated spot.