Large Research Facilities and Photon Science Divisions, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
Large Research Facilities and Photon Science Divisions, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland;
Proc Natl Acad Sci U S A. 2022 Feb 15;119(7). doi: 10.1073/pnas.2117906119.
X-ray free-electron lasers (FELs) deliver ultrabright X-ray pulses, but not the sequences of phase-coherent pulses required for time-domain interferometry and control of quantum states. For conventional split-and-delay schemes to produce such sequences, the challenge stems from extreme stability requirements when splitting Ångstrom wavelength beams, where the tiniest path-length differences introduce phase jitter. We describe an FEL mode based on selective electron-bunch degradation and transverse beam shaping in the accelerator, combined with a self-seeded photon emission scheme. Instead of splitting the photon pulses after their generation by the FEL, we split the electron bunch in the accelerator, prior to photon generation, to obtain phase-locked X-ray pulses with subfemtosecond duration. Time-domain interferometry becomes possible, enabling the concomitant program of classical and quantum optics experiments with X-rays. The scheme leads to scientific benefits of cutting-edge FELs with attosecond and/or high-repetition rate capabilities, ranging from the X-ray analog of Fourier transform infrared spectroscopy to damage-free measurements.
无射线自由电子激光（FEL）可提供超亮的 X 射线脉冲，但无法提供用于时域干涉测量和量子态控制的相干脉冲序列。对于传统的分束和延迟方案来说，要产生这种序列，挑战在于需要在分束埃（Ångstrom）波长光束时满足极端稳定性要求，因为最小的路径长度差异会引入相位抖动。我们描述了一种基于选择性电子束退化和加速器中的横向光束整形的 FEL 模式，结合了自种子光子发射方案。我们不是在 FEL 产生光子脉冲后对其进行分束，而是在光子产生之前在加速器中对电子束进行分束，从而获得具有亚飞秒持续时间的锁相 X 射线脉冲。时域干涉测量成为可能，从而可以同时进行 X 射线的经典和量子光学实验。该方案可带来具有阿秒和/或高重复率能力的前沿 FEL 的科学效益，从 X 射线模拟的傅里叶变换红外光谱到无损伤测量。
