In this paper, we report on multiple phases of efficient laser-driven ion acceleration from near-critical density plasma of Gaussian density profile. Tracking of high-energy accelerated ions in multidimensional particle-in-cell simulations reveals the development of accelerating fields affecting the particles and the contribution of each acceleration phase to final ion energies. While the acceleration of ions occurs in a short time interval when a steep (infinite) density gradient is present, the accelerating field affecting the most energetic ions has unexpected local maxima about 50 fs after the moment when ultrashort (30 fs) laser pulse completely left the target with smooth density gradients. This field can be attributed to the apex of electron filament created behind the transmitted laser pulse. Full 3D simulation confirms the observations in 2D simulations in terms of ion acceleration mechanisms. However, it shows a substantial reduction of maximum achievable ion energies and a larger angular spread of accelerated ions compared with 2D approach, which demonstrates the necessity of using computationally demanding full 3D geometry for similar numerical studies.

在本文中，我们报告了从高斯密度分布的近临界密度等离子体的多阶段高效激光驱动离子加速。在多维粒子内细胞模拟中跟踪高能加速离子揭示了影响粒子的加速场的发展以及每个加速阶段对最终离子能量的贡献。当存在陡峭（无限）密度梯度时，离子的加速会在很短的时间间隔内发生，但影响最高能离子的加速场在超短 (30 fs) 激光脉冲完全离开后约 50 fs 出现意外的局部最大值具有平滑密度梯度的目标。该场可归因于在传输的激光脉冲后面产生的电子灯丝的顶点。全 3D 模拟证实了 2D 模拟在离子加速机制方面的观察结果。然而，与 2D 方法相比，它显示了最大可实现离子能量的显着降低和更大的加速离子角扩展，这表明使用计算要求高的全 3D 几何进行类似数值研究的必要性。