Accuracy enhancement of laser-induced breakdown spectroscopy using a combination of a confinement ring and quadrupole discharge arc

The critical issue in laser-induced breakdown spectroscopy (LIBS) research is the uncertainty of the spectral signal and insufficient quantitative analysis accuracy. Spectral enhancement methods, such as discharge assistance and plasma spatial confinement, have been investigated as effective ways to increase analytical accuracy of LIBS. On this basis, this work develops a novel spectroscopic enhancement system that integrates a coaxial optical path, quadrupole discharge arc and confinement ring. A quadrupole discharge arc is utilized to generate a more uniform electric field around the sample to improve the stability of the discharge. Combined with a confinement ring, spectral signal stability and intensity can be further improved. Moreover, discharge arc parameters and dimensions of the confinement ring have been optimized to achieve better signal enhancement, resulting in an 11.96 times increase in signal intensity, a 29.14% reduction in relative standard deviation (RSD), and an improvement in the signal-to-noise ratio (SNR) from 52.1 to 205.6. Based on the enhanced spectrum, the accuracy and robustness of the quantitative analysis model for ash, volatile matter, and calorific value in coal samples are greatly improved, with the root mean square error (RMSE) for the test set decreasing from 1.45%, 0.489%, and 0.468 MJ kg⁻¹ to 1.09%, 0.361%, and 0.345 MJ kg⁻¹, respectively, and for the robustness test set decreasing from 1.36%, 0.395%, and 0.441 MJ kg⁻¹ to 0.921%, 0.312%, and 0.353 MJ kg⁻¹. Our work proposes a promising coupled enhancement method to improve the detection accuracy of LIBS, characterized by a straightforward, cost-effective setup with potential for industrial application.