Abstract：Laser-induced Breakdown Spectroscopy (LIBS) is a material composition analysis technology. It uses a pulsed laser to focus on the surface of the sample. When the laser ablates the sample, the plasma is generated. The spectrometer collects the spectrum，and the computer performs the elemental analysis. It has the advantages of simple and rapid operation and comprehensive detection elements. Traditional LIBS has the disadvantages of low detection sensitivity and high spectral background noise. Combining LIBS technology with cavity confinement can enhance spectral intensity, while some parameters such as signal-to-noise ratio (SNR) and plasma temperature are also effectively improved. In this paper, the cylindrical cavity of PLA and aluminum were fixed on the surface of the brass sample, with diameters of 5 mm and 6 mm. And each diameter corresponded to five different heights：1, 2, 3, 4, and 5mm, respectively. Three Cu plasma lines of Cu Ⅰ 510.55 nm, Cu Ⅰ 515.32 nm and Cu Ⅰ 521.82 nm were collected by the spectrometer and then were analyzed. The experimental results show that the spectral intensity is enhanced under each cavity confinement compared to without cavity. For the Cu 515.32 nm spectral line, the enhancement factor and signal-to-noise ratio under each cavity were studied. With the increase of the height of the cylindrical cavity, the enhancement factor firstly increases and then decreases, it reaches the maximum at the height of 4 mm. For a cavity of the same height and different diameter, it is larger at 5 mm than 6 mm in diameter. For a cavity of the same height and diameter, it is larger at the cavity of the aluminum material than PLA material. Under the current experimental conditions, when the height is 4 mm, and the diameter is 5 mm, the cavity of the aluminum material has the most obvious enhancement effect, the maximum enhancement factor is 28.29. The signal-to-noise ratio is consistent with the trend of the enhancement factor and reaches a maximum of 44.03 under the cavity of the aluminum material with a height of 4 mm and a diameter of 5 mm, which is 13.89 times compared to without cavity. In addition, the plasma temperature was calculated. The PLA cavity has little effect on the plasma temperature, while the plasma temperature increases obviously under the aluminum cavity, and excess value reaches a maximum of 467.35 K at 5 μs compared to without cavity. The cavity confinement device is simple and is convenient to combine with the LIBS system, and the enhanced spectral effect is obvious, so it has broad application prospects. This paper studied the influence of LIBS combined with cavity confinement of different materials on the spectrum of laser-induced breakdown Cu plasma, which has certain reference value for the selection of cavity materials.
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