Enhancement of optical emission generated from femtosecond double-pulse laser-induced glass plasma at different sample temperatures in air

In double-pulse laser-induced breakdown spectroscopy (DP-LIBS), the collinear femtosecond double-pulse laser configuration is experimentally investigated with different initial sample temperatures using a Ti:sapphire laser. The glass sample is ablated to produce the plasma spectroscopy. During the experiment, the detected spectral lines include two Na (I) lines (589.0 nm and 589.6 nm) and one Ca (I) line at the wavelength of 585.7 nm. The emission lines are measured at room temperature (22 °C) and three higher initial sample temperatures (T_s =100 °C, 200°C, and 250 °C). The inter-pulse delay time ranges from -250 ps to 250 ps. The inter-pulse delay time and the sample temperature strongly influence the spectral intensity, and the spectral intensity can be significantly enhanced by increasing the sample temperature and selecting the optimized inter-pulse time. For the same inter-pulse time of 0ps (single-pulse LIBS), the enhancement ratio is approximately 2.5 at T_s=200 °C compared with that obtained at T_s=22 °C. For the same inter-pulse time of 150 ps, the enhancement ratio can be up to 4 at T_s=200 °C compared with that obtained at T_s=22 °C. The combined enhancement effects of the different initial sample temperatures and the double-pulse configuration in femtosecond LIBS are much stronger than that of the different initial sample temperatures or the double-pulse configuration only.