Generation of X-ray spatiotemporal vortices via nonlinear Thomson scattering

Abstract High-energy vortex beams with transverse orbital angular momentum (TOAM) have significant applications in many fields. However, generating such beams with well-defined spatiotemporal (ST) field structures at energies beyond extreme ultraviolet is still a major challenge. Here, we demonstrate the generation of coherent X-ray spatiotemporal optical vortices (STOVs) with definitive mode-resolved, ST field-level structures through nonlinear Thomson scattering of a near-infrared STOV laser pulse by a relativistic electron beam in a nanometer-scale thickness. Our far-field time-domain radiation simulations confirm that the generated X-ray harmonics are STOV pulses with well-defined STOV structures, where the vortex charge scales linearly with the harmonic order, in accordance with TOAM conservation. The emission is highly collimated within approximately 4 mrad. The formation of coherent STOV structures requires tight temporal synchronization, spatial confinement and phase matching of the radiation fields from individual electrons in the electron beam. Excessive laser beam sizes induce spectral broadening and phase mismatches, which degrade coherence and suppress the emergence of well-defined STOV harmonics. This study presents a new approach for generating highly collimated X-ray STOVs, with potential applications in nuclear physics, ultrafast dynamics and structured light–matter interactions at the nanoscale.