The characterization of energetic protons generated in the ShenGuang-II UP petawatt laser interactions with foil targets has been systematically studied. The proton energy spectra and angular distributions are measured with a radiochromic film stack. It shows that the proton energy spectra have a Boltzmann distribution with temperature of about 2.8 MeV and cutoff energy of about 20 MeV. The divergence angles of protons vary from 10° to 60°, dependent on the proton energy. The proton source size and location are investigated via the proton point-projection mesh imaging. The proton virtual sources are found to locate tens to hundreds of microns in front of the foil target, depending on the proton energies. A Monte Carlo simulation estimates the diameter of the virtual proton source to be about 12 μm for the protons with energy of 16.8 MeV, which is much smaller than the laser focus size of about 50 μm. The spatial resolution of the 16.8 MeV proton imaging is quantified with the point spread function to be about 15 μm, which is consistent with the proton virtual source size. These results will be important for the users conducting experiments with the protons as a backlighting source on the ShenGuang-II UP petawatt laser.

中文翻译：

---

神光-II UP 拍瓦激光与箔靶相互作用中产生的高能质子的表征

系统研究了神光二号 UP 拍瓦激光与箔靶相互作用中产生的高能质子的表征。质子能谱和角度分布是用放射变色薄膜堆栈测量的。它表明质子能谱具有玻尔兹曼分布，温度约为2.8 MeV，截止能量约为20 MeV。质子的发散角从 10° 到 60° 不等，取决于质子能量。通过质子点投影网格成像研究质子源的大小和位置。根据质子能量，发现质子虚拟源位于箔靶前方数十至数百微米处。对于能量为 16.8 MeV 的质子，蒙特卡罗模拟估计虚拟质子源的直径约为 12 μm，远小于约 50 μm 的激光焦点尺寸。16.8 MeV 质子成像的空间分辨率用点扩散函数量化为约 15 μm，与质子虚拟源尺寸一致。这些结果对于用户在神光-II UP 拍瓦激光器上将质子作为背光源进行实验非常重要。