The use of ultrathin solid foils offers optimal conditions for accelerating protons to high energies from laser–matter interactions. When the target is thin enough that relativistic self-induced transparency sets in, all of the target electrons get heated to high energies by the laser, which maximizes the accelerating electric field and therefore the final ion energy. In this work, we first investigate how ion acceleration by ultraintense femtosecond laser pulses in transparent CH $_2$ solid foils is modified when turning from normal to oblique ( $45^\circ$ ) incidence. Due to stronger electron heating, we find that higher proton energies can be obtained at oblique incidence but in thinner optimum targets. We then show that proton acceleration can be further improved by splitting the laser pulse into two half-pulses focused at opposite incidence angles. An increase by ${\sim }30\,\%$ in the maximum proton energy and by a factor of ${\sim }4$ in the high-energy proton charge is reported compared to the reference case of a single normally incident pulse.

中文翻译：

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斜入射和碰撞脉冲对相对论透明超薄目标激光驱动质子加速的影响

超薄固体箔的使用为将质子从激光-物质相互作用加速到高能提供了最佳条件。当目标足够薄时，相对论自感透明开始，所有目标电子都被激光加热到高能量，从而最大化加速电场，从而最大化最终离子能量。在这项工作中，我们首先研究了超强飞秒激光脉冲如何在透明 CH 中加速离子 $_2$ 实心箔在从正常转向倾斜时被修改（ $45^\circ$ ) 发病率。由于更强的电子加热，我们发现可以在倾斜入射但更薄的最佳靶材中获得更高的质子能量。然后，我们表明，通过将激光脉冲分成两个聚焦在相反入射角的半脉冲，可以进一步提高质子加速度。增加了 ${\sim }30\,\%$ 在最大质子能量和一个因子 ${\sim }4$ 与单个垂直入射脉冲的参考情况相比，报告了高能质子电荷。