来自自由电子激光振荡器的可快速切换的X射线角动量
Rapidly Switchable X-ray Angular Momentum from a Free Electron Laser Oscillator
AI总结：
本研究利用X射线自由电子激光振荡器的针孔镜，仅通过调整电子束动能实现可快速切换的X射线涡旋OAM模式，切换时间低于200微秒，脉冲能量达百微焦量级，为可控X射线涡旋生成提供了新方案。
摘要：
携带可调谐轨道角动量（Orbital Angular Momentum, OAM）的X射线涡旋是X射线表征技术中的一种新兴工具。然而，与可见光波段涡旋光束的产生相比，以可控方式产生X射线涡旋已被证明颇具挑战。在此，我们利用X射线自由电子激光振荡器（X-ray free-electron laser oscillator, XFELO）攻克了这一难题，该装置可产生具有可切换OAM的强相干X射线。本方案利用XFELO中的针孔镜，仅调整电子束的动能，即可产生可经编程在不同OAM模式间动态切换的涡旋光束，无需额外光学元件。基于当前在建的1 MHz重复频率装置（即SHINE）的标称参数，我们通过数值模拟验证了l = ±1和l = ±2的OAM模式的主动生成，以及通过失谐XFELO的电子束能量实现这些模式间的快速切换。实时切换可在200 μs内完成，同时输出脉冲能量可达100 μJ量级。
英文摘要：
X-ray vortices carrying tunable Orbital Angular Momentum (OAM) are an emerging tool for X-ray characterization technology. However, in contrast to the generation of vortex beams in the visible wavelength region, the generation of X-ray vortices in a controlled manner has proved challenging. Here, we overcome this challenge using an X-ray free-electron laser oscillator (XFELO), which can produce intense coherent X-rays with switchable OAM. Using the pinhole mirror in an XFELO, this scheme adjusts only the kinetic energy of the electron beam to produce vortex beams that can be programmed to dynamically change between different OAM modes without the need for additional optical elements. With the nominal parameters of currently constructing 1 MHz repetition rate facility (i.e. SHINE), the active formation of the OAM modes of l = ${\pm}$1 and l = ${\pm}$2 and the rapid switching between them by detuning the electron beam energy of the XFELO are numerically illustrated. The real-time switching can be achieved within 200 $μ$s, while the output pulse energy can reach the 100 $μ$J level.
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