基于对强飞秒激光大气传输的非线性薛定谔方程的变分法, 模拟研究飞秒激光大气传输成丝特性。 研究了在是否考虑多光子吸收损耗的情况下,激光成丝状态的演化。研究表明:多光子吸收损耗会破坏自聚 焦与等离子体散焦之间的动态平衡,进而引起成丝的不稳定性;在不同的入射功率下,成丝的起点位置会发 生移动;在实验室条件下, pin?3pcr 时才可能形成多次聚焦成丝传输。 继续增加激光入射功率时,光束因强烈聚焦发生崩塌而成多丝结构。

Based on the variational principle of nonlinear Schr?dinger(NLS) equation describing laser pulses propagation in air, the properties of femtosecond filamentation were studied by using numerical simulation method. Numerical results were derived on the developing process of filamentation under the situations of whether or not taking account of multiphoton absorption dissipation (MPA). It is shown that a dynamic equilibrium between optical self-focusing and plasma defocusing will be broken due to the MPA, which can induce instability of femtosecond filamentation. The first foci of the filaments are displaced for different incidence laser power. Further investigation reveals that stabe filamentation propagation described by defocusing-refocusing cycles can only arise for power pin?3pcr in laboratory. With the incidence power gradually increasing, the beam will undergo optical collapse due to intense focusing, and then the formation of femtosecond multiple filamentation(MF) can be obtained.