Enhancement characteristics of laser-induced plasma confined by hemispherical cavities in different materials
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A hemispherical cavity can be used to improve the sensitivity of laser-induced breakdown spectroscopy by increasing the emission spectra of the plasma. In this work, laser-induced plasma plume images were obtained with and without confinement. The results have confirmed that the reason for the signal enhancement caused by the hemispherical cavity was the reflected shockwave “compressing” effect. The dependence of spectral signal enhancement on the material property of the cavities was investigated. Four cavities in different materials, which include K-resin, aluminum alloy, photosensitive resin and nylon, were used to confine the plasma. It has shown that the material physical properties of the cavities influence the enhancement effect. We found that the main influencing factor was surface roughness of the material. Smoother cavity surfaces induced stronger enhancement effects due to the larger specular reflection component of the reflected shockwave and the more intense subsequent interaction between the plasma and shockwave. The spectral intensities of the characteristic lines approximately doubled with surface roughness values changing from 0.2 to 16.1.
The authors are grateful for financial support from the National Natural Science Foundation of China (Grant Nos. 11504091, 61775052, 61674052, 31500300).
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