Selective Control of THz Magnon–Light Interactions via Light Polarization

Optical control over magnon creation and annihilation is essential for magnon‐based quantum devices. However, conventional optomagnonic processes face a fundamental bottleneck, namely that the probabilities of magnon creation (Stokes scattering) and annihilation (anti‐Stokes scattering) are inherently symmetric. Here, we demonstrate that this symmetry can be broken in the canted antiferromagnet Sm 0.6 Er 0.4 FeO 3 single crystal. We identify two distinct magneto‐optical effects in this material that serve as independent channels for magnon–light interactions: magnetic circular birefringence (MCB) facilitates helicity‐conserving scattering, while magnetic linear birefringence (MLB) governs helicity‐changing scattering. By controlling the coherent interference between MCB and MLB via tuning the linear polarization of light, we selectively suppress either Stokes or anti‐Stokes Raman scattering. This selective suppression yields an extreme anti‐Stokes‐to‐Stokes intensity ratio exceeding 20 (13 dB) for quasi‐antiferromagnetic (qAFM) magnons, thereby enabling a polarization‐selective Raman scattering pathway. We found that the giant precession ellipticity of the antiferromagnetic magnon strongly amplifies the contribution of MLB. Our results extend this effect from previous YIG systems (GHz magnons) into the THz regime. These findings establish rare‐earth orthoferrites as a versatile platform for polarization‐controlled magnon–light interactions, paving the way for engineering terahertz (THz) antiferromagnetic magnonic devices.