A multi-physics numerical model for laser-induced optical breakdown and laser-plasma interaction in a non-equilibrium gas is presented, accounting for: production of priming electrons via multi-photon ionization, energy absorption, cascade ionization, induced hydrodynamic response, and shock formation and propagation. The gas is governed by the Navier-Stokes equations, with non-equilibrium effects taken into account by means of a two-temperature model. The space-time dependence of the laser beam is modeled with a flux-tube formulation for the Radiative Transfer Equation. The flow governing equations are discretized in space using a second-order finite volume method. The semi-discrete equations are marched in time using an implicit-explicit (IMEX) dual time-stepping strategy, where diffusion and chemistry are solved implicitly, whereas convection is explicit. Application to a 20 ns long 50 mJ pulse laser-induced breakdown in quiescent O₂ shows the advantages of this temporal discretization during and just after the laser pulse, while a less-expensive symmetric Strang splitting (for implicit chemistry) is sufficient for the post-breakdown gas dynamics after ≃ 0.1textmu s. The integrated model is shown to reproduce key features of corresponding experiments.

提出了一种在非平衡气体中激光诱导的光击穿和激光-等离子体相互作用的多物理场数值模型，其解释为：引发的产生电子通过多光子电离，能量吸收，级联电离，诱发的流体动力学响应以及激波的形成和传播。气体由Navier-Stokes方程控制，并通过两个温度模型考虑了非平衡效应。激光束的时空相关性用辐射传递方程的通量管公式建模。流量控制方程使用二阶有限体积法在空间上离散。半离散方程使用隐式-显式（IMEX）对偶时间步长策略在时间上进行求解，其中扩散和化学过程被隐式求解，而对流则是显式的。在20 ns长的50 mJ脉冲激光诱导的静态O ₂击穿中的应用图1显示了在激光脉冲期间和之后进行时间离散的优势，而成本更低的对称Strang分裂（用于隐式化学分析）足以满足text 0.1textmu s之后的分解后气体动力学。所示的集成模型可重现相应实验的关键特征。