New spectroscopic techniques improve the detection of trace elements in liquids

Laser-induced breakdown spectroscopy (LIBS) is a rapid chemical analysis technique that has been developed for trace element analysis
in gases, liquids, and solids.
It uses high-power laser pulses to cause a brief burst of high-temperature plasma in the sample
.
When the plasma cools, it emits spectral peaks
corresponding to the elements in the periodic table.
In recent years, LIBS has been extended by filamentous induced breakdown spectroscopy (FIBS), which has higher sensitivity and better stability
.
However, FIBS is inherently limited
by the intensity of the guided laser of the filament itself.

Plasma grating induced breakdown spectroscopy (GIBS) can overcome the limitations
of FIBS.
However, effective laser ablation remains a huge challenge in liquids, as plasma excitation is hampered by the inevitable shock waves and the generation of microbubbles, as well as large variations
in liquid pressure around the ablation area.

According to Advanced Photonics Nexus, researchers recently combined FIBS and GIBS as an effective technique
for sensitive detection of trace metals in liquids.
They demonstrated a combination of strong nonlinear interactions of filaments (coplanar and non-collinear) with different plasma gratings to achieve a technological innovation
known as "F-GIBS" (filament and plasma grating-induced breakdown spectroscopy).
F-GIBS analysis
of aqueous solutions using fluid jets.

This plasma excitation technique cleverly avoids the adverse effects
of liquid surface fluctuations and bubbles caused by violent plasma explosions.
The two-femtosecond laser beam is non-linearly coupled to create a plasma grating covering almost the entire jet and excite the liquid sample
.
The third filament is aligned, nonlinearly coupled
to the plasma grating in the same plane (perpendicular to the fluid jet).
Nonlinearly coupled filaments enter the jet through the air-water interface without random filament
breaks.

Professor Zeng Heping, senior author of the State Key Laboratory of Precision Spectroscopy at East China Normal University, said: "F-GIBS provides a promising aqueous solution trace element detection technology with improved sensitivity
.
The regenerative excitation of plasma gratings demonstrated in this work may help to enhance some other well-developed double-pulse LIBS technologies, such as plasma reheating and laser-induced fluorescence, which facilitates the convenient use
of lasers from the same source within a shorter time delay.
”