State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.
Institute of Quantum Materials and Physics, Henan Academy of Sciences, Zhengzhou 450046, China.
Phys Rev Lett. 2023 May 5;130(18):186901. doi: 10.1103/PhysRevLett.130.186901.
Polarizing electron beams using light is highly desirable but exceedingly challenging, as the approaches proposed in previous studies using free-space light usually require enormous laser intensities. Here, we propose the use of a transverse electric optical near field, extended on nanostructures, to efficiently polarize an adjacent electron beam by exploiting the strong inelastic electron scattering in phase-matched optical near fields. Intriguingly, the two spin components of an unpolarized incident electron beam-parallel and antiparallel to the electric field-are spin-flipped and inelastically scattered to different energy states, providing an analog of the Stern-Gerlach experiment in the energy dimension. Our calculations show that when a dramatically reduced laser intensity of ∼10^{12} W/cm^{2} and a short interaction length of 16 μm are used, an unpolarized incident electron beam interacting with the excited optical near field can produce two spin-polarized electron beams, both exhibiting near unity spin purity and a 6% brightness relative to the input beam. Our findings are important for optical control of free-electron spins, preparation of spin-polarized electron beams, and applications in material science and high-energy physics.
利用光来极化电子束是非常理想的，但极具挑战性，因为之前使用自由空间光的研究方法通常需要极高的激光强度。在这里，我们提出利用横向电场光学近场来有效地极化相邻的电子束，方法是利用在相匹配的光学近场中强的非弹性电子散射。有趣的是，一束非极化入射电子束的两个自旋分量——平行和反平行于电场——被自旋翻转并散射到不同的能量状态，在能量维度上提供了斯特恩-格拉赫实验的模拟。我们的计算表明，当使用显著降低的激光强度约为 10^{12} W/cm^{2}和 16 μm 的短相互作用长度时，与激发的光学近场相互作用的非极化入射电子束可以产生两个自旋极化的电子束，两者都表现出近于 1 的自旋纯度和相对于输入束的 6%的亮度。我们的发现对于自由电子自旋的光学控制、自旋极化电子束的制备以及在材料科学和高能物理中的应用都非常重要。
