利用渡越辐射研究超热电子在固体靶中的输运过程

为了探索超热电子的输运过程，在100 TW掺钛蓝宝石飞秒激光器上利用光学CCD相机和OMA光学多道分析仪，分别在靶背表面法线方向测量了光发射空间分布图案和光谱. 实验测量结果显示，光发射空间分布图案呈圆盘状，在圆盘中明亮而强的光信号呈局部化分布，该现象表明，超热电子在输运的过程中存在成丝效应，引起严重的不稳定性；光发射光谱在3倍频和3/2倍频附近出现尖峰，分别是3次谐波和3/2次谐波，这一现象归因于超热电子束在传输的过程中产生的微束团而引起的相干渡越辐射(CTR)；光发射光强随靶厚度的增加而减小. 关键词： 超热电子 相干渡越辐射 输运 不稳定性

Study of transport of hot electrons in solid targets using transition radiation

For studing the transport of hot electrons in solid targets by transition radiation, the image pattern of spatial distribution and spectrum of optical emission were measured at the normal direction from the rear side of targets employing optical CCD camera and OMA optical multi-channel spectrometer on the 100 TW femtosecond laser facility.The image pattern of spatial distribution has a disc-shape, in which is distributed a bright localized signal, which shows the filament effect during hot electron transport. The spectrum of optical emission has sharp peaks near the 3 and 3/2 multiple of the fundamental frequency, corresponding to the third-order harmonic and 3/2-order harmonics, respectively, which is ascribed to the coherent transition radiation (CTR) generated by microbunches of hot electron beams produced in transport. The intensity of transition radiation decreases with the increase of target thickness.