The terahertz (THz) temporal waveform and spectrum from a longitudinal electrically biased femtosecond filament is studied experimentally. The initial direction of the electron motion inside the unbiased filament plasma is deduced from the transformation of the THz temporal waveform with applied fields of opposite polarities. Furthermore, a spectrum shift to lower frequency of the THz spectrum is observed in the presence of a biased field. It agrees well with theoretical predictions.

中文翻译：

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来自纵向电场偏置的飞秒长丝的太赫兹辐射

实验研究了纵向电偏置飞秒细丝的太赫兹（THz）时间波形和频谱。无偏压灯丝等离子体内部的电子运动的初始方向是从具有相反极性的施加电场的太赫兹时间波形的变换推导出来的。此外，在存在偏置场的情况下，观察到频谱向太赫兹频谱的较低频率偏移。它与理论预测非常吻合。