A comparative spectroscopic study of single and dual pulse laser produced UV tin plasmas

Abstract

A comparative study of single-pulse (SP) and dual-pulse laser-induced breakdown spectroscopy (DP-LIBS) using two Q-switched Nd:YAG lasers emitting at 532nm is presented. Both lasers were combined in the same direction (collinear beam scheme) to focus on planar Sn targets at ambient pressure. The effect of the delay times between the incident laser pulse and the ICCD gate, placement of the laser beam focal position with respect to the illuminated surface, incident laser irradiance, and ambient argon pressure on the signal intensity enhancement for the dual pulse scheme have been studied. Atomic and ionic emission lines of Sn were recorded in the 272–296nm UV spectral region. By using the DP-LIBS excitation technique, the intensity of Sn lines was enhanced by nearly seven times as compared to the single pulse signal that could help the analytical performance of the LIBS technique in terms of increasing sensitivity and reducing self-absorption effects for Sn targets. In the case of the DP-LIBS scheme, the intensities of the atomic Sn I at 283.9nm were recorded at different optimal angles of 45° and 90° and were compared. This comparison was done at different positions of the laser beam focus with respect to the illuminated surface (at 2.45mm in front of the surface, on the surface, at 1.7mm and 4.7mm behind the surface). Furthermore, in the DP-LIBS scheme, an intensity enhancement of the atomic Sn I line at 283.9nm occurs when the signal was recorded at an angle of 90° to the plasma expansion along the direction of the incident laser beam and the detector set at short delay times. The investigation proved that an optimized value of short delay times between the incident laser pulse and the ICCD gate is required. Variations in the electron temperature (Te) and electron number density (Ne) as a function of gate delay time and laser irradiance have been studied by using the emission lines of neutral tin. Special attention was paid to possible self-absorption of the different transitions. The micro-craters created by SP and DP laser ablation were compared using a reflection optical microscopy (ROM).