Angle-Resolved Polarimetry of Smith–Purcell Radiation

High Resolution Image Download MS PowerPoint Slide We report angle-resolved, full-Stokes polarimetric measurements of Smith–Purcell radiation (SPR) generated by an electron beam interacting with subwavelength silicon gratings. By reconstructing the polarization ellipse at each emission angle, we reveal a strongly angle-dependent vectorial polarization distribution of SPR, exhibiting controllable transitions among linear, elliptical, and circular polarization states. By varying the grating orientation and duty cycle, we demonstrate the deterministic control of the full polarization state of SPR. Moreover, since the electron beam size is significantly smaller than the typical dimensions of the grating unit cell, lateral translation of the electron beam alters the generated polarization states. The measurements are in agreement with finite-difference time-domain electromagnetic simulations, showing that the polarization is governed jointly by the geometric symmetry of the grating and the excitation position of the electron beam. This work establishes SPR from nanostructured gratings as a versatile and compact platform for polarization engineering of classical and quantum light emission over a potentially broad spectral range from terahertz frequencies up to the X-ray regime.