激光脉冲宽度对激光诱导击穿光谱强度和烧蚀形貌的影响OA

[Background]The dual-pulse LIBS(DP-LIBS)technology can effectively enhance the spectral intensity of LIBS and has received widespread attention in LIBS analysis.[Purpose]To understand the enhancement mechanism of traditional collinear dual pulse LIBS and long-short collinear dual pulse LIBS spectra,a comparative study was conducted on two DP-LIBS with different laser excitation schemes,i.e.the conventional collinear dual nanosecond pulse excitation scheme,and the long-short collinear dual-pulse excitation scheme which combines a microsecond pulse and a nanosecond pulse.[Method]The enhancement mechanism and variation trend of spectral intensity were investigated by systematically analyzing the laser ablation morphology and LIBS spectra collected under different inter-pulse delays,spectral acquisition delays and laser pulse energy in both DP-LIBS modes.[Results]The results show that,in conventional collinear DP-LIBS,the spectral intensity increases rapidly within a short delay time of 0-2 μs,but remains relatively high in the longer delay range of 2-14 μs.And the optimal inter-pulse delay is around 4 μs in conventional collinear DP-LIBS.In contrast,the optimal inter-pulse delay for the long-short collinear DP-LIBS is approximately 25 μs,which is determined by the peak power timing of the long-pulse laser.[Conclusions]In the conventional DP-LIBS configuration,spectral enhancement is more sensitive to the energy variations of the second pulse than to those of the first pulse.In the long-short pulse scheme,increasing the energy of the long-pulse laser facilitates sample heating and surface modification,thereby enhancing spectral intensity.However,excessive long-pulse laser energy might cause sample melting and material ejection,which in turn diminishes the ablation efficiency of the subsequent short-pulse laser and reduces the overall spectral intensity.Further analysis of the ablation morphology reveals that the conventional collinear DP-LIBS tends to produce deeper ablation craters,whereas the long-short collinear DP-LIBS is more likely to generate larger ablation craters.