New Research Sheds Light on How Ambient Gases Affect LIBS Signal Quality

In a recent study, a team of researchers from Tsinghua University and Qinghai University conducted an analysis of laser-induced breakdown spectroscopy (LIBS) signals, uncovering new information about how the properties of ambient gases impact LIBS signal quality. This study, which was led by Zhe Wang of Tsinghua University and Qinghai University, provides vital information about how to improve the precision and repeatability.

LIBS is known as a rapid chemical analysis technique (2). It works by focusing a high-powered laser pulse on a material to create a microplasma and then analyzing the emitted light to determine elemental composition (1) Several advantages of this technique are that it conducts elemental analysis quickly, requires no sample preparation, and allows for thin-sample analysis without substrate interference (2). However, one key limitation of this technique is that it can have signal instability. This instability, often linked to fluctuations in the plasma generated during the process, has posed a significant barrier to the widespread adoption of LIBS in high-precision applications (1).

Portable X-ray fluorescence (XRF) analyzers for analyzing elemental composition of artifacts. Generated by AI. | Image Credit: © Textures & Patterns - stock.adobe.com

Although it is an accepted fact that ambient gases have played a role in these inconsistencies, a clear understanding of how specific gas properties influence LIBS signals has not been discovered yet.

In this study, Wang and his team developed an experimental approach to isolate and examine the impact of three main ambient gas properties, which are specific heat ratio, molar mass, and ionization energy (1). The research team successfully built out comparisons between standard atmospheric conditions and those created using customized gas compositions by doing two things: 1) they engineered the gas mixtures, and 2) they utilized plasma diagnostics, including rapid imaging, shadowgraph techniques, and optical emission spectroscopy (OES) (1).

The team did not analyze secondary gas properties and instead only focused on the primary influences. Three custom gas mixtures were formulated by blending six pure gases in controlled ratios, with each mixture differing from air by only one of the three target properties (1). This design allowed the team to assess the role of each property in isolation.

The study’s findings reveal how the three ambient gas properties impact LIBS signal repeatability. Specifically, variations in specific heat ratio and molar mass influence the strength and structure of shockwaves produced during plasma formation (1). In turn, these shockwaves affect the consistency of the LIBS signal.

Further, the properties of the ambient gases also modulate the energy transfer processes within the plasma, which are critical to the overall signal intensity. These include laser energy absorption efficiency, the allocation of energy between the gaseous environment and the sample species, and the rate of heat dissipation from the plasma (1).

According to the researchers, a higher sound speed, resulting from a more favorable specific heat ratio or molar mass, leads to weaker shockwaves and more stable plasma behavior, which translates to improved signal repeatability (1). Similarly, adjusting ionization energy levels affects the core position of the plasma, with higher positions reducing the intensity of the back-pressing process (1).

By establishing these cause-and-effect relationships, Wang's team has not only provided deeper insights into the physics of plasma evolution in LIBS, but also delivered practical guidelines for optimizing ambient gas compositions to enhance signal quality (1).

As LIBS continues to grow in importance for applications ranging from environmental monitoring to materials science and forensic investigations, this research could potentially be used to significantly expand its usability and reliability. With these new insights, scientists and engineers now have a roadmap to manipulate ambient conditions and extract more accurate data from one of the most promising techniques in modern spectroscopy.

References

1. Song, Y.; Hou, Z.; Yu, X.; et al. Exploring the Impact Mechanism of Ambient Gas Properties on Laser-induced Breakdown Spectroscopy to Guide the Raw Signal Improvement. Anal. Chimica Acta 2025, 1335, 343464. DOI: 10.1016/j.aca.2024.343464
2. Applied Spectra, What is LIBS? Applied Spectra. Available at: https://appliedspectra.com/technology/libs.html (accessed 2025-04-24).