Fig. 1. Schematic diagram of solid substrate-assisted enhancement structure. (a) Overall structure of solid substrate-assisted enhancement LIBS system; (b) internal structure of solid substrate-assisted enhancement LIBS system

Fig. 2. Comparison of spectral enhancement effect of different basal calcium elements (393.4, 396.8, 422.7 nm)

Fig. 3. Variations of seawater LIBS spectra with operating time assisted by silicon substrate

Fig. 4. Variations of Ca, Na and K radiation intensity with substrate operating time assisted by silicon substrate

Fig. 5. Photograph of the surface of a silicon substrate after 240 min of continuous operation

Fig. 6. Photographs of solid substrate-assisted enhancement of LIBS system in shallow-sea test. (a) LIBS system just touching the seawater; (b) LIBS system located at 1 m underwater

Fig. 7. Enhancement effects of substrate-assisted enhancement of LIBS system for underwater in-situ work with different times

Fig. 8. Photograph of silicon substrate surface after 30 min of continuous operation

Fig. 9. Photograph of in-situ work of the substrate-enhanced deep-sea LIBS

Fig. 10. 1503 m water depth substrate-enhanced LIBS spectra, where the spike at 532 nm is unfiltered clean laser light