Characterization of ultrafast laser-ablation plasma plumes at various Ar ambient pressures

Abstract

Recently, we reported morphological changes in ultrafast laser ablation plumes in varying ambient pressures [Diwakar et al., J. Appl. Phys. 116, 133301 (2014)]. In this paper, we report the emission features of fs laser ablated brass plasma plumes at various Ar background pressure levels ranging from vacuum to atmospheric conditions and correlated to changes in plume morphology. Spatially resolved wavelength dispersed images of the plume were recorded for characterizing the spectral features at various pressure levels and also used for obtaining spatial distribution of Cu I and Zn I species in the plume, signal-to-noise ratios, and fundamental parameters of the plasma, specifically temperature and density. The spatial evolution of plasma temperature and density showed significant changes at various ambient pressure levels; these results were correlated to morphological changes seen in the plume images. Optical time-of-flight profiles were used to study time evolution of various species in the plume and indicated oscillations of ablation plumes at intermediate pressure levels. Possible mechanisms for observed changes in plume shape, optical emission intensity, and dual peak structures in time-of-flight profiles are discussed.