Transformation of the frequency-angular spectrum of THz emissions produced by a single-color laser filament plasma under an external electrostatic field of various strength is experimentally studied. While there is no any static electric field, THz emission is predominantly generated in the low-frequency spectral range around 0.1 THz and propagates within a hollow cone. When the electric field is applied, the transition from the hollow cone to a filled one is observed with the field strength rise and the THz emission frequency within the range of 0.3–0.5 THz. Higher frequency emissions of ∼1 THz fills the whole cone with the emission maximum along the laser filament axis.

实验研究了单色激光灯丝等离子体在不同强度的外部静电场下产生的太赫兹发射的频率角谱的变换。虽然没有任何静电场，但 THz 发射主要在 0.1 THz 左右的低频频谱范围内产生，并在空心锥内传播。当施加电场时，观察到从空心锥到实心锥的转变，场强升高，太赫兹发射频率在 0.3-0.5 THz 范围内。约 1 THz 的高频发射充满整个锥体，发射最大值沿激光灯丝轴。