The efficient generation, accurate detection, and detailed physical tracking of energetic electrons are of applied interest for high harmonics generation, electron-impact spectroscopy, and femtosecond time-resolved scanning tunneling microscopy. We here investigate the generation of photoelectrons (PEs) by exposing plasmonic nanostructures to intense laser pulses in the infrared (IR) spectral regime and analyze the sensitivity of PE spectra to competing elementary interactions for direct and rescattered photoemission pathways. Specifically, we measured and numerically simulated emitted PE momentum distributions from prototypical spherical gold nanoparticles (NPs) with diameters between 5 and 70 nm generated by short laser pulses with peak intensities of 8.0 × 1012 and 1.2 × 1013 W/cm2, demonstrating the shaping of PE spectra by the Coulomb repulsion between PEs, accumulating residual charges on the NP, and induced plasmonic electric fields. Compared to well-understood rescattering PE cutoff energies for strong-field photoemission from gaseous atomic targets (10× the ponderomotive energy), our measured and simulated PE spectra reveal a dramatic cutoff-energy increase of two orders of magnitude with a significantly higher contribution from direct photoemission. Our findings indicate that direct PEs reach up to 93 % of the rescattered electron cutoff energy, in contrast to 20 % for gaseous atoms, suggesting a novel scheme for the development of compact tunable tabletop electron sources.

中文翻译：

---

等离子体纳米粒子直接和再散射强场光电子发射的增强截止能量

高能电子的高效产生、准确检测和详细的物理跟踪对高次谐波产生、电子碰撞光谱和飞秒时间分辨扫描隧道显微镜具有应用意义。我们在这里通过将等离子体纳米结构暴露于红外 (IR) 光谱范围内的强激光脉冲来研究光电子 (PE) 的产生，并分析 PE 光谱对直接和再散射光电子发射途径的竞争性基本相互作用的敏感性。具体来说，我们测量并数值模拟了由峰值强度为 8.0 × 10 的短激光脉冲产生的直径在 5 到 70 nm 之间的原型球形金纳米粒子 (NP) 发射的 PE 动量分布12和 1.2 × 1013宽/厘米2个, 通过 PE 之间的库仑排斥力、在 NP 上积累残余电荷和感应等离子体电场来展示 PE 光谱的整形。与众所周知的气态原子靶强场光电发射的再散射 PE 截止能量（10 倍有质动力能量）相比，我们测量和模拟的 PE 光谱显示截断能量显着增加了两个数量级，其中贡献显着更高直接光电发射。我们的研究结果表明，直接 PE 可达到高达 93% 的再散射电子截止能量，而气态原子仅为 20%，这表明一种开发紧凑型可调桌面电子源的新方案。