Effects of aerosols and laser cavity seeding on spectral and temporal stability of laser-induced plasmas: applications to LIBS

Abstract

The spectral and temporal effects of laser cavity seeding and aerosol presence in the laser-induced plasma volume are investigated with the goal of examining factors affecting the precision of laser-induced breakdown spectroscopy. Improvements in the temporal stability of laser-induced breakdown initiation were observed with laser cavity seeding. However, laser cavity seeding produced no significant improvement in analyte precision for a range of gas-phase atomic emission lines, including nitrogen, hydrogen, and carbon. In contrast, greater shot-to-shot analyte precision, as measured by a nearly 60% reduction in relative standard deviation, was realized with the elimination of concomitant aerosols from the analyte sample stream. Such findings are consistent with the expected interactions of ambient aerosols and the laser-induced breakdown process.

Laser-Induced Breakdown Spectroscopy (LIBS), Part I: Review of Basic Diagnostics and Plasma—Particle Interactions: Still-Challenging Issues within the Analytical Plasma Community

“…This is verified in the context of plasma volume measurements, particle sampling rate considerations, and direct imaging studies. [260][261][262][263] The plasma-particle processes must also be framed in the context of the overall plasma lifetime (~10-100 ls for typical pulse energies) and the analytical timescales (i.e., detector delays and gates), which typically range from~1-50 ls following the initial laser pulse. 264 With this framework in mind, Fig.…”

Investigation of helium addition for laser-induced plasma spectroscopy of pure gas phase systems: Analyte interactions and signal enhancement

“…Accordingly, to further establish single-shot LIBS-based techniques as an integrated analytical tool for detection and quantitative analysis of aerosols and dilute gaseous species, it is desirable to seek improvements in the precision and the overall method detection limit. In earlier studies, we have explored these goals in terms of the laserplasma coupling [11], the laser pulse stability [13], and the use of double-pulse laser excitation [14]. In the current work, the effects of helium addition to the gaseous analyte sample stream are explored as a means to further improve the LIBS signal response.…”

Three-dimensional distribution of signal from single monodisperse aerosol particles in a laser induced plasma: Initial measurements

“…However, if a particle is located within the focused laser beam, or there are many particles within the plasma, the laser absorption process may be different enough to affect the resulting plasma properties. This effect may be minimized by using a pulse energy well above the breakdown threshold of the gas [14]. Finally, it should be noted that the particle vaporization process itself is expected to depend strongly on whether the particle is located within the laser beam, whether it is located in a "hot spot" [15] early in the plasma formation, or whether it is engulfed by the expanding plasma subsequent to the laser pulse.…”