Self-absorption of emission lines in picosecond-laser-produced gold plasmas

Abstract

Ultrashort laser ablation offers several advantages in various applications compared to traditional nanosecond laser ablation techniques. Despite providing a lower damage threshold, cold ablation with high precision, the impact of self-absorption effects in ultrashort laser-produced plasmas (LPPs) significantly affects the assessment of plasma parameters and analytical outcomes in Laser-Induced Breakdown Spectroscopy (LIBS) analysis. This study investigated the impact of laser energy, analyte concentration, and acquisition gate delay on the self-absorption of emission lines from picosecond LPPs (ps-LPPs) of gold targets at atmospheric pressure. We used four gold targets (24 carat gold, 22 carat gold, 18 carat gold, and Hepatizon) with varying concentrations of gold and copper. To analyze the self-absorption effects in ps-LPP, we examined four neutral emission lines of ps-LIBS spectra (Au I: 267.59 and 627.81 nm; Cu I: 327.98 and 510.55 nm). We observed that with an increase in laser pulse energy, there is a corresponding rise in the self-absorption of emission lines under ambient pressure. This increase in analyte species concentration leads to an elevation in the self-absorption of emission lines. Additionally, as the temporal delay of acquisition extends, self-absorption intensifies.