不同功率下的飞秒激光在水中形成的脉冲压缩和超连续谱

本文研究了飞秒激光脉冲在水中的传输情况.通过改变不同的激光输入功率进行模拟，我们发现从输入功率略高于到远远高于发生自聚焦的临界功率,分别是群速度色散和多光子电离多光子吸收阻止了自聚焦导致的脉冲塌陷，当多光子电离和多光子吸收主导传输时，脉冲能被压缩到几个光学周期.在频域，多光子电离能引起很强的蓝移,而多光子吸收能对这种蓝移起到抑制作用。

Propagation of femtosecond light pulses in water is investigated. By changing input power from slightly above to highly above threshold for self-focusing, it is shown that either group velocity dispersion (GVD) or multi-photon ionization (MPI) and multi-photon absorption (MPA) may arrest the collapse. When MPI and MPA dominate the propagation, the pulse can be self-compressed to a few optical cycles. In spectral domain, MPI alone induces a strong blue shift. MPA can restrain this strong blue shift.