超热电子输运背向光辐射的实验研究

Experimental study of optical radiation of hot electrons transport in targets at the rear-side radiation

在100 TW掺钛蓝宝石飞秒激光器上利用光学CCD相机和光学多道分析仪,分别在靶背法线方向测量了超热电子光辐射的空间分布和光谱.测量结果显示:光辐射空间分布图案呈圆环状,而辐射区域有发散角和光强分布,且包含多种辐射成分.光辐射光谱在800 nm附近出现尖峰,是激光的基频(ω0)波,这一现象归因于超热电子束在输运的过程中产生的微束团而引起的相干渡越辐射(CTR).随着激光能量的增加,CTR光谱峰向红光方向移动,基频波红移的主要原因是由于等离子体临界面的迅速膨胀.如果考虑超热电子的产生和加热机理,共振吸收和真空加热对超热电子都有贡献,其中占主导地位的加热机理则是共振吸收对电子的加热.

This paper reports the image pattern of spatial distribution and spectrum of optical radiation measured in the normal direction from the rear side of the target employing optical CCD camera and optical multi-channel analysor on the 100 TW femtosecond laser facility.The image pattern of spatial distribution has a ring-shape,the region of optical radiation has larger radiation angle and optical intensity distribution,and the radiation is comprised of many components.The spectrum of optical radiation shows a sharp peak near 800？nm,which is attributed to the laser fundamental（ω_0）,and is ascribed to the coherent transition radiation（CTR） generated by microbunches of hot electron beams generated in transport.With the increase of the laser energy,the peak of the CTR moves further to the long wavelength side,the red shift is caused by the expansion of the critical density surface.The acceleration of hot electron comes mainly from resonance absorption.