Detection of trace elements in liquids improved by new spectroscopy technique

Laser induced breakdown spectroscopy (LIBS) is a rapid chemical analysis technology which has been well developed for the analysis of trace elements in gases, liquids and solids. It uses a high-power laser pulse to elicit short-lived high-temperature plasma in a sample. As the plasma cools, it emits spectral peaks that correspond to the elements in the periodic table. Recent exploration has extended LIBS via filament induced breakdown spectroscopy (FIBS), which has better sensitivity and higher stability. Yet FIBS is inherently limited by the intensities of the laser driven into the filament itself.

Plasma lattice-induced breakdown spectroscopy (GIBS) could overcome the limitations of FIBS. However, efficient laser ablation in liquid remained a major challenge because plasma excitations are hampered by the inevitable generation of shock waves and microbubbles as well as dramatic changes in liquid pressure surrounding the ablated region.

As reported in Advanced photonic nexus, researchers have recently combined FIBS and GIBS as an efficient technique for sensitive detection of trace metals in liquids. They demonstrated the combination of strong non-linear interactions of filaments (coplanar and non-collinear) with different plasma lattices, to achieve a technical breakthrough called ‘F-GIBS’ (plasma lattice and filament induced breakdown spectroscopy). F-GIBS has been implemented using fluid jets to analyze aqueous solutions.

This plasma excitation technique clearly avoids the harmful influence of liquid surface fluctuation and bubbles formed by violent plasma explosions. Two femtosecond laser beams were non-collinearly coupled to establish plasma gratings that cover nearly the entire jet and excite the liquid sample. A third filament was aligned to couple nonlinearly with the plasma gratings in the same plane (vertical to the fluid jet). The nonlinearly coupled filaments entered the fluid jet through the air-water interface without random filament breaks.

According to senior author Heping Zeng, a professor at East China Normal University’s Key Laboratory of Precision Spectroscopy, “F-GIBS provides a promising technique for the detection of trace elements in aqueous solutions with improved sensitivity. The regenerative excitations of plasma gratings demonstrated in this work may serve to improve some other already well-developed double-pulse LIBS techniques, such as plasma heating and laser-induced fluorescence, with plasma re-excitation in much shorter time delays , facilitating the convenient use of lasers from the same sources.

Reference: Hu M, Li F, Shi S, et al. Detection of trace metals in water by plasma filament and lattice-induced disruption spectroscopy. apn. 2023;2(1):016008. doi: 10.1117/1.APN.2.1.016008

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