As intense, ultrashort, kHz-repetition-rate laser systems become commercially available, pulse cumulative effects are critical for laser filament-based applications. In this work, the pulse repetition-rate effect on femtosecond laser filamentation in air was investigated both numerically and experimentally. The pulse repetition-rate effect has negligible influence at the leading edge of the filament. Clear intensity enhancement from a high-repetition pulse is observed at the peak and tailing edge of the laser filament. As the repetition rate of the laser pulses increases from 100 to 1000 Hz, the length of the filament extends and the intensity inside the filament increases. A physical picture based on the pulse repetition-rate dependent ‘low-density hole’ effect on filamentation is proposed to explain the obtained results well.

基于光电流模型，通过数值模拟和理论分析，研究了静电场幅值对飞秒激光气体微等离子体中太赫兹辐射的影响。结果显示，随着外加静电场幅值的增大，太赫兹辐射的强度呈线性增大；当外加电场极性相反时，太赫兹波形整体反转；当外加电场与线偏振激发激光的偏振方向呈一定夹角时，太赫兹辐射的偏振方向完全由外加电场方向决定。数值模拟结果与已有的实验结果相符。理论分析表明，这个线性依赖、极性反转以及夹角依赖均源于等离子体产生之后的静电加速的主导作用。