Speaker
Description
Free-electron radiation underpins modern light sources, from R\"ontgen's X-rays to today's fourth-generation X-ray free electron lasers (XFELs). When electrons interact with periodic electromagnetic environments, they emit radiation with a spectrum covering microwaves to X-rays. In recent years, the rapid progress of nanophotonics, advances in high-intensity lasers, and the cross-disciplinary integration of these fields have aroused great interest in controlling electron radiation. In particular, coherent emission has attracted significant attention. In particular, near-field photonics such as surface plasmon polaritons (SPPs), with their strong subwavelength confinement, offer a promising platform for compact radiation sources and integrated photonics.
Here, we demonstrate both the mechanism and experimental realization of free-electron--driven coherent amplification of terahertz SPPs. By coherently seeding SPPs with femtosecond laser pulses and synchronizing free-electron pulses, we achieve phase-locked interactions and observe energy gains exceeding three orders of magnitude within a 1.5-mm interaction length, a performance comparable to high-gain FELs.
Furthermore, we propose that quasi-periodic magnetic arrays arise in plasma through Weibel instability ($\sim 10^4$\;T), serves as an undulator or wiggler. In this configuration, the electrons undergo transverse oscillations, and by tuning the plasma parameters, the emitted radiation can be tuned continuously from the ultraviolet to the X-ray regime.
In addition, we also introduce the on-chip light source configuration, constructed with a dielectric nanopillar array. Laser excitation of such periodic structures couples into electromagnetic near fields, that provide periodic transverse acceleration to relativistic electrons. Through relativistic frequency up-conversion, this configuration produces tunable high-energy photons spanning ultraviolet to X-ray and $\gamma$-ray frequencies, while offering high operational stability and reduced damage risk.
By exploiting novel optical materials and constructing diversified periodic electromagnetic environments for free-electron interactions, we establish a versatile framework for radiation spanning from THz to X-ray frequencies. Our work not only demonstrates compact coherent free-electron sources but also expands the concept and implementation of micro-undulators, laying the foundation for multidimensional free-electron--periodic structure interactions and opening new avenues for miniaturized, tunable, and coherent electron-driven radiation.