Generation of Relativistic Structured Spin-Polarized Lepton Beams

Relativistic structured spin-polarized (SSP) particle beams, characterized by polarization structures, are of critical importance in a wide range of applications, such as material properties investigation, imaging, and information storage. However, the generation of relativistic SSP beams faces significant challenges. Here, we put forward a novel method for generating relativistic SSP lepton beams via employing a state-of-the-art THz source. Building upon our foundational work on velocity-matched spin rotation in dielectric-lined waveguides [Phys. Rev. Lett. 134, 075001 (2025)PRLTAO0031-900710.1103/PhysRevLett.134.075001], we present the first demonstration of spin-polarization mode matching-a novel mechanism that establishes a direct relation between waveguide modes and beam polarization states. This breakthrough enables precise spatial control over spin structures at relativistic energies, generating customizable spin-polarization configurations such as spiderlike, azimuthal, and helical structures. Such SSP beams have the potential to generate high-energy structured photon beams and open a new avenue for research on relativistic structured particle beams, especially in nuclear physics, high-energy physics, materials science, and atomic physics.