Copper signal characteristics using collinear LS-DP-LIBS for underwater measurement

The collinear long-short double-pulse laser-induced breakdown spectroscopy (LS-DP-LIBS) was employed in the detection of underwater copper samples. Discrete emission lines were obtained using LS-DP-LIBS with an appropriate delay between two pulses, while characteristic emission lines were covered by continuous background and noise using LIBS with a single pulse. In the condition of LS-DP-LIBS, signal characteristics of the measured spectra at different experimental parameters including long-pulse width, lens-to-sample distance (LTSD), and long-pulse energy have been investigated to determine the optimal condition. The results indicated that the long-pulse width and the long-pulse energy were closely related to the formation of a cavitation bubble, thus affecting the plasma state and signal characteristics for underwater measurement. The parameter of the LTSD imposed an effect on the spectral signal through changing the ablation mass of the sample and the plasma temperature. The experimental results demonstrated the feasibility of the underwater measurement of metal samples using the collinear LS-DP-LIBS and showed a significant signal improvement through this method. With further development, it is of great potential to apply this new method based on LIBS to ocean exploration.