Fig. 1. Schematic of experimental setup for underwater orthogonal DP-LIBS

Fig. 2. Schematic of timing sequence utilized for LIBS experiments

Fig. 3. Effect of acquisition delay time on SP-LIBS. (a) Spectra of SP-LIBS at different acquisition delay time; (b) intensity and SNR of Ba II 455.4 nm as a function of acquisition delay time in SP-LIBS

Fig. 4. Effect of acquisition delay time on DP-LIBS. (a) Spectra of DP-LIBS at different acquisition delay time; (b) intensity and SNR of Ba II 455.4 nm as a function of acquisition delay time in DP-LIBS

Fig. 5. Schematic of relative position of two laser foci (1st arrow represents first laser beam, 2nd arrow represents second laser beam)

Fig. 6. Effect of relative position of two laser foci on DP-LIBS. (a) Spectra of DP-LIBS corresponding to different ΔX; (b) intensity of Ba II 455.4 nm as a function of ΔX

Fig. 7. Intensity of Ba II 455.4 nm as a function of laser energy in SP-LIBS

Fig. 8. Intensity of Ba II 455.4 nm as a function of first laser energy in DP-LIBS

Fig. 9. Effect of the second laser energy on DP-LIBS. (a) Spectra of DP-LIBS corresponding to different second laser energies; (b) intensity of Ba II 455.4 nm as a function of the second laser energy in DP-LIBS

Fig. 10. LIBS spectra obtained under optimized experimental conditions. (a) SP-LIBS; (b) DP-LIBS

Fig. 11. Spectra of underwater SP-LIBS and DP-LIBS (td=1.2 μs)

Fig. 12. Calibration curves for Ba II 455.4 nm spectral line. (a) SP-LIBS; (b) DP-LIBS