The process of high energy electron acceleration along the surface of grating targets (GTs) that were irradiated by a relativistic, high-contrast laser pulse at an intensity $I=2.5\times 10^{20}~\text{W}/\text{cm}^{2}$ was studied. Our experimental results demonstrate that for a GT with a periodicity twice the laser wavelength, the surface electron flux is more intense for a laser incidence angle that is larger compared to the resonance angle predicted by the linear model. An electron beam with a peak charge of ${\sim}2.7~\text{nC}/\text{sr}$ , for electrons with energies ${>}1.5~\text{MeV}$ , was measured. Numerical simulations carried out with parameters similar to the experimental conditions also show an enhanced electron flux at higher incidence angles depending on the preplasma scale length. A theoretical model that includes ponderomotive effects with more realistic initial preplasma conditions suggests that the laser-driven intensity and preformed plasma scale length are important for the acceleration process. The predictions closely match the experimental and computational results.

中文翻译：

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高强度激光脉冲激发的表面等离子体波的相对论电子加速

沿光栅目标 (GT) 表面的高能电子加速过程，这些目标被相对论性的高对比度激光脉冲以一定强度照射 $I=2.5\times 10^{20}~\text{W}/\text{cm}^{2}$ 进行了研究。我们的实验结果表明，对于具有两倍于激光波长的周期性的 GT，与线性模型预测的共振角相比，激光入射角越大，表面电子通量就越强。具有峰值电荷的电子束 ${\sim}2.7~\text{nC}/\text{sr}$ , 对于有能量的电子 ${>}1.5~\text{MeV}$ , 被测量了。使用与实验条件相似的参数进行的数值模拟也显示出在较高入射角下的电子通量增强，这取决于等离子体前尺度长度。一个包含有质动力效应和更真实的初始前等离子体条件的理论模型表明，激光驱动的强度和预形成的等离子体尺度长度对于加速过程很重要。预测与实验和计算结果非常吻合。