Effect of vortex beam shaping on determination of trace elements in Al alloy by double-pulse laser-induced breakdown spectroscopy

Abstract This study proposed a double-pulse laser-induced breakdown spectroscopy (DP-LIBS) signal enhancement method based on the shaping of vortex beams, effectively addressing the low-energy utilization of the second pulse in collinear DP-LIBS systems and significantly improving the detection sensitivity of trace elements in aluminum (Al) alloys. This study built a conventional collinear DP- LIBS system, and the second pulse laser was shaped into a vortex beam using a vortex half-wave plate. This study confirms that vortex beam shaping can enhance the spectral signal intensity and improve the stability of the plasma. The effects of spectral acquisition delay and inter-pulse delay on the performance of the vortex beam shaping technique in DP-LIBS were systematically investigated through experimental studies. The results demonstrate that compared with the traditional Gaussian beam method, the vortex beam shaping technology on average increases the spectral line intensity of the characteristic elements in the Al alloy sample by an average factor of 2.22, and the signal-to-background ratio increases significantly to 1.58. Additionally, the average value of relative standard deviation of the characteristic spectral lines was reduced from 8.54% to 4.39%. Trace elements such as Pb and Ti were also detected. Further analysis of transient plasma images confirmed that the vortex beam shaping technique enhances LIBS signals by modulating the spatial energy distribution and helical phase fronts of the second pulse laser, thereby altering the plasma evolution dynamics.