Intense X-Ray Vortices Generation via Wavefront Shaping in High-Gain Free-Electron Lasers

The x-ray vortex optical beam, distinguished by its topological charge and orbital angular momentum, offers new insights in probing complex electronic structures, enhancing material characterization, and advancing high-resolution imaging techniques. Here we propose a novel and reliable method to generate intense x-ray vortices with tunable wavelengths in high-gain free-electron lasers (FELs). By simply adjusting the wavefront tilt of the radiation pulse during the FEL gain process, high-quality vortex beam can be amplified until saturation. Compared with existing methods for FEL vortex generation, the proposed technique offers broader wavelength tunability and can be easily implemented in high-gain FEL facilities, regardless of the operating modes.