Structures on the front surface of thin foil targets for laser-driven ion acceleration have been proposed to increase the ion source maximum energy and conversion efficiency. While structures have been shown to significantly boost the proton acceleration from pulses of moderate-energy fluence, their performance on tightly focused and high-energy lasers remains unclear. Here, we report the results of laser-driven three-dimensional (3D)-printed microtube targets, focusing on their efficacy for ion acceleration. Using the high-contrast ($\sim {10}^{12}$) PHELIX laser ($150\mathrm{J}$, ${10}^{21}\mathrm{W}/{\mathrm{cm}}^2$), we studied the acceleration of ions from $1\text{−}\mu \mathrm{m}$-thick foils covered with micropillars or microtubes, which we compared with flat foils. The front-surface structures significantly increased the conversion efficiency from laser to light ions, with up to a factor of 5 higher proton number with respect to a flat target, albeit without an increase of the cutoff energy. An optimum diameter was found for the microtube targets. Our findings are supported by a systematic particle-in-cell modeling investigation of ion acceleration using 2D simulations with various structure dimensions. Simulations reproduce the experimental data with good agreement, including the observation of the optimum tube diameter, and reveal that the laser is shuttered by the plasma filling the tubes, explaining why the ion cutoff energy was not increased in this regime.

中文翻译：

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来自高强度皮秒激光脉冲照射的微结构目标的离子加速。

已经提出了用于激光驱动离子加速的薄箔靶的前表面上的结构，以增加离子源的最大能量和转换效率。虽然已经显示出结构可显着提高中能量通量脉冲产生的质子加速度，但在紧密聚焦和高能量激光器上的性能仍不清楚。在这里，我们报告激光驱动的三维（3D）打印的微管目标的结果，重点是它们对离子加速的功效。使用高对比度（$〜{10}^{12}$）PHELIX激光（$150\mathrm{Ĵ}$， ${10}^{21}\mathrm{w\; ^}/{\mathrm{厘米}}^2$），我们研究了来自 $\mathrm{1个}\text{-}\mu \mathrm{米}$覆盖有微柱或微管的厚箔片，我们将其与扁平箔片进行了比较。前表面结构显着提高了从激光到光离子的转换效率，相对于平坦的目标，其质子数最多提高了5倍，尽管没有增加截止能量。发现了微管靶的最佳直径。我们的发现得到了使用具有不同结构尺寸的2D模拟的离子加速的系统细胞内颗粒模型研究的支持。仿真结果重现了实验数据，包括观察最佳管径，并显示出激光被被填充管的等离子所遮挡，从而解释了为何在这种情况下离子截止能量没有增加。