Cavity confinement microwave enhanced laser-induced plasma modulation method: Improvement in signal intensity and repeatability

Abstract

Microwave-enhanced laser-induced breakdown spectroscopy (ME-LIBS) is a promising analysis technique for trace element detection with the advantage of high signal intensity. However, the shot-to-shot repeatability of the ME-LIBS signal is relatively low, which affects the precision of the result and limits quantification performance. A cavity confinement microwave-enhanced laser-induced plasma (CC-ME-LIP) modulation method is proposed to improve the repeatability of the ME-LIBS signal. During the plasma evolution, cavity confinement provides an environment that regulates plasma around the microwave probe, controls plasma expansion, and minimizes interaction with the atmosphere. This behavior enhances the stability of the plasma morphology, leading to improved signal repeatability. In addition, confinement increases the energy transfer process within the plasma by the superimposition of two methods, resulting in a stronger signal intensity. The CC-ME-LIP modulation method is applied to the brass sample. The relative standard deviation (RSD) of the different copper and zinc lines has been reduced, along with an improvement of the intensity enhancement factor (IEF). For example, Cu 521.820 nm line RSD reduced from 29.11% (ME-LIBS) to 17.12% (CC-ME-LIBS) with an IEF of 1.08. The result demonstrated that the proposed approach significantly improves the repeatability of the ME-LIBS signal, thereby increasing the overall signal quality. To gain a deeper understanding, a detailed analysis of the mechanisms behind the increased signal intensity and improved repeatability was further investigated.

Graphical abstract

Keywords

microwave-enhanced laser-induced breakdown spectroscopy / plasma modulation / cavity confinement / intensity enhancement / pulse-to-pulse repeatability

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Declarations

The authors declare that they have no competing interests and there are no conflicts.

Novelty statements

The goal of this study is to use the CC-ME-LIBS modulation approach to increase the shot-to-shot repeatability of ME-LIBS signals. While earlier research has mostly concentrated on enhancing signal intensity in ME-LIBS, this work presents a method of using cavity confinement to improve signal stability over several laser pulses.

Acknowledgements

The authors are grateful for the financial support from the National Key Research and Development Program of China (No. 2023YFB4102900), the Carbon Neutrality and Energy System Transformation (CNEST) Program led by Tsinghua University, and Huaneng Group Science and Technology Research Project (No. HNKJ22-H105).

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