Laser-induced breakdown spectroscopy (LIBS), with its unique advantages such as no need for complex sample pretreatment and capability for real-time in-situ detection, demonstrates significant potential for deep-sea mineral composition analysis. However, the deep-sea environment is characterized by extreme conditions including high pressure, low temperature, and high salinity, which significantly influence the generation and evolution of laser-induced plasma as well as the associated cavitation dynamics. Therefore, systematic investigation into the multi-physics coupling mechanisms of laser-induced plasma and cavitation in deep-sea extreme environments holds substantial theoretical significance and engineering application value. This study establishes a numerical model based on the compressible multiphase flow theoretical framework, capable of accurately describing the entire process of laser-induced plasma and cavitation evolution in deep-sea extreme environments. The model fully considers the key physical mechanisms involved in the laser-matter interaction, primarily including the following core modules: first, the multiphase flow governing equations are formulated based on compressible flow theory, employing the volume of fluid method to track the evolution of gas-liquid-plasma multiphase interfaces; second, an ionization model based on the local thermodynamic equilibrium assumption is introduced to describe the generation and species distribution of laser ablation-induced plasma; third, a gas-plasma mixture equation of state suitable for deep-sea high-pressure environments is constructed to accurately describe the thermodynamic properties of the gas-plasma mixture under high-pressure conditions; finally, the laser energy deposition process is coupled through source terms to achieve a complete description of the laser-matter interaction. Based on the above model, numerical simulations of laser-induced plasma and cavitation evolution under different ocean depths are systematically conducted, and the results are validated against deep-sea simulation experimental data, ensuring the validity and computational accuracy of the model. The simulation results reveal the significant mechanisms through which ocean depth influences the physical characteristics of laser-induced plasma and cavitation dynamics. The study shows that with increasing ocean depth, the elevated ambient pressure enhances the confinement effect on the plasma, resulting in a decreased initial expansion rate of the plasma, a slightly reduced peak plasma temperature, but an extended duration of the high-temperature region. Regarding cavitation evolution, increasing depth leads to a significant reduction in the maximum cavitation bubble radius and a shortened collapse time, while the instantaneous pressure peak during bubble collapse increases markedly, and the bubble oscillation period exhibits an exponential decay pattern. Furthermore, the deep-sea high-pressure environment significantly affects the cavitation bubble collapse mode, transitioning from multiple pulsation collapses in shallow water to a single collapse in deep water.
 

laser-induced plasma,deep-sea extreme environment,cavitation dynamics,compressible multiphase flow