基于扩展的非线性薛定谔方程及与其耦合的电子密度演化方程, 理论研究了超短激光强脉冲在水中的非线性传输特性。理论模型综合考虑了衍射、正常群速度色散, 多光子吸收、自聚焦及激光诱导产生的等离子体对光脉冲的自散焦效应。采用有限差分法模拟得到超短脉冲在传输过程中轴向上光功率密度和等离子体密度的时空分布。系统分析了超短脉冲在水中传输的动力学过程, 讨论了非线性自聚焦和等离子体自散焦效应在脉冲传输过程中的竞争关系。同时研究了不同入射激光能量, 脉宽和聚焦条件对等离子体丝的时空结构和脉冲能流横向分布的影响。该研究将有助于理解和推动超短光脉冲在激光医学、激光安全防护和水中激光加工中的应用。

The propagation properties of ultrashort laser pulses in water is investigated with the extended nonlinear Schrdinger equation and the electron density equation. With the theoretical model that incorporates the diffraction, normal group-velocity dispersion, multiphoton absorption, self-focusing and self-defocusing effects generated by the laser-induced eletron plasma, the spatio-temporal distribution of the on-axis laser power density and plasma density during the propagation are obtained by fininte difference method. Simulation of the underlying propagation dynamics of the ultrashort laser in water reveals that the competitive relationship between nonlinear self-focusing and self-defocusing during the pulse propagation. Moreover, the influence of laser energy, pulse duration and focusing geometry on the structure of plasma filament and the reshaping of energy fluence are discussed. The results may be benefical to understand and push forward the application of the ultrashort laser pulses in medicine, laser safety and processing in water.