尾波场中传播的激光脉冲的频率漂移

Frequency shift of laser pulse propagating in wakefield

一个超短超强激光脉冲在另一个超短脉冲激发的尾波场中传播时 ,如果这两个脉冲之间距离合适 ,第二个脉冲前半部分经历的电子密度比后半部分高 ,其后部群速度高于前部 ,脉冲将被压缩 ,频率向高频方向移动 .用PIC粒子模拟证实了这一点 ,模拟得到的频移与理论结果吻合 .另外 ,非线性效应使得最有效频移对应的脉冲之间的间距比线性理论估计值大 .

When two ultrashort and ultrahigh laser pulses spacing an appropriate distance propagate through tenuous plasma, the second laser pulse will be compressed and shift to higher frequency because the anterior part of the pulse experiences the higher plasma density and propagates with lower group velocity while the rear part of the pulse experiences the lower plasma density and propagates with higher group velocity. The frequency shift of the second pulse in our PIC simulation is in good agreement with the theoretical predication. Furthermore, the optimum intervals between the two pulses is larger than that estimated with linear theory.