Lin Jinpu, Batson Thomas, Nees John, Thomas Alexander G R, Krushelnick Karl
Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, MI, 48109, USA.
Sci Rep. 2020 Oct 27;10(1):18354. doi: 10.1038/s41598-020-75418-6.
We investigate MeV-level attosecond electron bunches from ultrashort-pulse laser-solid interactions through similarities between experimental and simulated electron energy spectra. We show measurements of the bunch duration and temporal structure from particle-in-cell simulations. The experimental observation of such bunches favors specular reflection direction when focusing the laser pulse onto a subwavelength boundary of thick overdense plasmas at grazing incidence. Particle-in-cell simulation further reveals that the attosecond duration is a result of ultra-thin ([Formula: see text]tenth of a micron) gaps of zero electromagnetic energy density in the modulated reflected radiation, while the bunching (locally peaked electron concentration) comes from the highly-directional electron angular distribution acquired by the electrons in a grazing incidence setup. To isolate a single electron bunch, we perform simulations using 1-cycle laser pulses and analyze the effect of carrier-envelop phase with particle tracking. The duration of the electron bunch can be further decreased by increasing the laser intensity and the focal spot size, while its direction can be changed by tuning the preplasma density gradient.
我们通过实验和模拟电子能谱之间的相似性，研究了超短脉冲激光与固体相互作用产生的兆电子伏特级阿秒电子束。我们展示了来自粒子模拟的束团持续时间和时间结构的测量结果。当以掠入射角将激光脉冲聚焦到厚过密等离子体的亚波长边界上时，对这种束团的实验观察有利于镜面反射方向。粒子模拟进一步揭示，阿秒持续时间是调制反射辐射中零电磁能量密度的超薄（[公式：见正文]十分之一微米）间隙的结果，而聚束（局部峰值电子浓度）则来自于在掠入射角设置中电子获得的高度定向电子角分布。为了分离单个电子束团，我们使用单周期激光脉冲进行模拟，并通过粒子跟踪分析载波包络相位的影响。通过增加激光强度和焦斑尺寸，可以进一步缩短电子束团的持续时间，而通过调整预等离子体密度梯度可以改变其方向。
