Improvements in discrimination of bulk and trace elements in long-wavelength double pulse LIBS

Abstract

In this work we study the effectiveness of long-wavelength heating in double pulse (DP) LIBS, quantitatively comparing figures of merit with those from traditional single pulse (SP) LIBS. The first laser pulse serves as the source of sample ablation, creating an aerosol-like plume that is subsequently reheated by the second laser pulse. At power densities used, the long-wavelength CO 2 laser pulse does not ablate any of the solid sample in the atmospheric conditions investigated, meaning plasma emission and enhanced signal can be entirely attributed to the reheated plume rather than increased sample ablation. The signal discrimination was improved significantly using long-wavelength DP-LIBS. For bulk elemental analysis, DP-LIBS provided maximum enhancements of about 14 and 15 times for S/N and S/B, respectively, compared to SP-LIBS using the same quantity of ablated sample. For trace elemental analysis, maximum enhancements of about 7 and 4 times for S/N and S/B, respectively, were observed. These improvements are attributed to effective coupling between the second heating pulse and expanding plume and more efficient excitation of plume species than from the single pulse alone. Most significant improvements were observed in the case of low prepulse energy and minimal sample ablation. While bulk elemental analysis observed improvements for all prepulse energies studied, trace element discrimination only significantly improved for the lowest prepulse energy studied.

Spatio-temporal evolution of uranium emission in laser-produced plasmas

“…It has to be pointed out that both signal to noise (S/N) and S/B ratios are routinely used for comparing performance metrics of emission analysis. Typically S/N and S/B trends are often similar, but can occasionally be inconsistent due to the transient nature of a signal [29,30].…”

A Comparative Study of Single-pulse and Double-pulse Laser-Induced Breakdown Spectroscopy with Uranium-containing Samples

“…In previous studies the combination of the Nd:YAG-CO 2 pulse lasers for DPLIBS shows a reduction in the damage to target and thus meets criteria discussed for SNM sensing. 24 The combination of a half wave plate and polarizing cube permits adjustment of the output pre-pulse energy without modifying the pulse duration or the spatial profile. The experiments entail a near collinear geometry because of different laser wavelengths and consequently differing focusing optics: A pre-pulse hits the sample at a slight angle (approximately 5°) to perpendicular while a heating pulse is perpendicular to the target.…”

Advances in explosives analysis—part II: photon and neutron methods

“…Using a CO 2 laser as the second pulse efficiently reheats the plasma plume through an inverse Bremsstrahlung absorption process, without increasing the quantity of ablated mass [166,182]. More recently a geometry-dependent, singlebeam-splitting LIBS approach obtained signal enhancement (~5×) resulting from the angle and energy of the second beam and not the timing [183].…”