Relativistic spin-polarized lepton beams are pivotal for high-energy physics, nuclear physics, and materials science, but existing spin control methods suffer from bulkiness, poor beam quality, or limited structure customization. We exploit terahertz waveguides’ unique electromagnetic modes to develop a spin evolution theory, clarify lepton spin-waveguide mode interaction mechanisms, and propose schemes for ultrafast spin switching (transverse to longitudinal) with >98% efficiency and compressed energy spread. Further, we establish waveguide mode-spin structure correspondence, enabling generation of spider-like, azimuthal, and helical structured polarized beams while preserving beam quality. This work resolves key bottlenecks in polarized lepton source development, opening new avenues for high-resolution imaging and topological structure excitation.

waveguide,polarized beam generation,Polarization Modulation,High Energy Density Physics