Self-Synchronized Soft X-Ray and Infrared Free-Electron Lasers from a Single Prebunched Electron Beam
Phys. Rev. Lett. 137, 185001 – Published 26 October, 2026
DOI: https://doi.org/10.1103/3kmz-18bp
Abstract
Ultrafast pump-probe spectroscopy combining intense infrared and x-ray pulses is an important tool for investigating complex structural and electronic dynamics in materials. However, current configurations combining external sources and x-ray free-electron lasers (FELs) often suffer from high system complexity, inherent timing jitter, or limited pulse properties. Here, we experimentally demonstrate the generation of intrinsically synchronized soft x-ray (SXR) and midinfrared (MIR) FELs from a single prebunched electron beam. Sequentially passing the beam through an SXR undulator followed by an MIR amplifier reveals a highly synergistic process: the initial periodic MIR density modulation boosts the SXR FEL pulse energy, while robustly surviving the intense SXR FEL to drive high-power, narrowband MIR radiation. Extending this scheme to lower terahertz frequencies suppresses SXR power, but this can be compensated by machine tuning. Originating from the same electron bunch, the dual-color pulses inherently maintain a precise, constant time delay. This intrinsically synchronized scheme establishes a highly reliable platform tailored for both SXR-pump and infrared-probe and infrared-pump and SXR-probe experiments.
