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

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 532 nm 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 272–296 nm 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 283.9 nm 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 2.45 mm in front of the surface, on the surface, at 1.7 mm and 4.7 mm behind the surface). Furthermore, in the DP-LIBS scheme, an intensity enhancement of the atomic Sn I line at 283.9 nm 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).

► A comparative study of SP- and DP-LIBS using two lasers at different focus positions is presented.
► The collinear DP-LIBS is superior as compared to SP-LIBS.
► The ideal position of the Sn I line at 283.9 nm is 4.7 mm behind the surface at 90o at short delay times.
► Employing a SP is a cheaper if the research tolerates a low resolution.
► If high resolution is required the DP technique is preferable.