飞秒激光与固体靶相互作用的前向快电子束发散研究

为了研究前向快电子束的发散问题，采用飞秒激光辐照平面铜靶，以电子角分布仪和氟化锂(LiF)热释光探测器探测快电子的前向发散角。实验显示前向快电子束发散角均在95°(半高宽FWHM)以上。理论计算指出预等离子体中电子的初速度以及加速后的电子在靶内碰撞效应均不是产生大发散角的重要原因。根据激光-等离子体相互作用理论，等离子体中的电磁场才是导致前向快电子束产生较大发散角的主要原因。这个研究为获取较小发散角的前向快电子束提供了实验设置的依据。

A study for the divergence of forward fast-electron-beam produced by a femtosecond laser pulse on a solid target

In order to investigate the divergence of forward fast-electron-beam, the divergence angle of fast-electron-beam produced in the interaction of femtosecond laser with Cu target has been measured by using an angular distribution instrument adding the lithium fluoride (LiF) thermo-luminescent dosimeters. The results show that the divergence angle of forward fast-electron-beam is above 95° (Full width at half maximum, FWHM) level. The theoretic calculation show that the muzzle velocity of electrons from pre-plasma and the collision effect generated by the transmission of fast electrons through a target are not mostly factor. A larger divergence angle of the forward fast-electron-beam is attributed to the electromagnetic field. This investigation is helpful to select the laser and the target parameter for getting a fast electron beam with small divergence angle.