Suppression of self-absorption in laser-induced breakdown spectroscopy using a double pulse orthogonal configuration to create vacuum-like conditions in atmospheric air pressure

Abstract

Self-absorption, which is known to severely disturb identification of the emission peak intensity in emission-based spectroscopy, was first studied using ordinary single pulse laser-induced breakdown spectroscopy (LIBS). It was found that severe self-absorption, with an evident self-reversal, occurs in the resonance emission lines of high concentration Na, K, and Al, and thus it is impossible to obtain the linear calibration curve required for quantitative analysis. To overcome this problem, we introduce a double pulse orthogonal technique in which the first laser is fired in a parallel orientation at a varied distance of 2–6 mm from the sample surface. It is well known that the strong shock wave generated by this laser irradiation temporarily creates a vacuum-like condition immediately in front of the sample surface. This action is followed by a second laser irradiation oriented perpendicular to the sample surface. The sample ablated by the second laser irradiation expands following the shockwave excitation process in the vacuum-like air atmosphere created by the first laser. The obtained spectra of the resonance emission lines of high concentration Na, K, and Al are free from the self-reversal and weakly affected by the self-absorption effect. A linear calibration curve that intercepts near zero point for K element over a wide concentration range is also demonstrated in this study. This simple modification is considered notably helpful in overcoming the self-absorption that occurs in ordinary single pulse atmospheric pressure LIBS.

Sulfur Detection in Soil by Laser Induced Breakdown Spectroscopy Assisted by Multivariate Analysis

“…There are several factors that can explain the less successful results of the S, MIN, MAX normalization methods. Among them, the most important are the possible presence of self-absorption [24] and matrix effects [23,25], which are unfortunately unavoidable. An extra problem arises from the formation of craters on the samples' surface, even though starch powder has been used for limiting crater formation.…”

Sensitive elemental analysis of bismuth brass under minimal sample ablation with target-enhanced orthogonal double-pulse laser-induced breakdown spectroscopy

“…Second, in ODP-LIBS, self-absorption effect can be significantly reduced in both reheating and pre-ablation schemes. [4,5] This will be very helpful for quantitative analysis if resonant lines are selected.…”

Evaluation of electrolyte element composition in human tissue by laser-induced breakdown spectroscopy (LIBS)

“…Since the LIBS emission peaks follow a Lorentzian distribution, different peak shapes result, depending on the signal intensity. Therefore, it is impossible to draw reliable conclusions regarding increases and decreases in LIBS signals from the comparison between low- and high-intensity peaks 16 , 17 . These shortcomings pose major challenges in clinical biomarker studies that use LIBS spectra and thus limit the reliability of analytical, quantitative assays, which should be used in clinical biomarker assays 18 .…”