超热电子产生的靶后相干渡越辐射光谱实验研究

利用OMA光学多道分析仪测量了激光与薄膜靶相互作用中产生的辐射光谱，在靶后观察到红移的二次谐波发射. 这种二次谐波是v×B加热产生的、具有微脉冲结构的超热电子束在等离子体-真空边界产生的相干渡越辐射(CTR). 随着激光能量的增大，红移峰向长波方向移动，光谱同时发生展宽. 分析认为，等离子体临界面的迅速膨胀是导致二次谐波红移的主要原因. 随着预脉冲能量的增大，临界面膨胀速度增大，导致了发射峰更大的红移. 实验还测量了靶面法线方向的辐射光谱，观察到基频辐射的红移和展宽. CTR为诊断临界面的运动方向和速度提供了一种新的方法. 关键词：相干渡越辐射超热电子超短超强激光等离子体相互作用

Observation of the rear-side coherent transition radiation generated by hot electrons

The red-shifted second harmonic emission of the laser light is observed in the laser propagation direction on the rear side of a foil target irradiated by femtosecond laser pulses. The emission is attributed to the coherent transition radiation (CTR) when the hot electrons accelerated by the v×B heating process traverse the solid-vacuum boundary. The red shift is caused by the expansion of the critical density surface towards the vacuum side. With the increase of the prepulse energy, the peak of the CTR moves further to the long wavelength side causing the broadening of the spectrum. The measurements of the CTR provide a potential diagnosis to the movement of the critical surface in the laser-plasma interaction process.