Polarization-Resolved Terahertz Near-Field Nanoscopy of Graphene

Scattering-type scanning near-field optical microscopy (s-SNOM) provides access to nanoscale optical responses beyond the diffraction limit. However, at low terahertz (THz) frequencies, quasi-electrostatic models predict that highly conductive graphene behaves as a near-total reflector to large in-plane-momentum (<i>q</i>) near fields, essentially insensitive to layer number. Here, we probe graphene from monolayer to few-layer using polarization-resolved terahertz near-field nanoscopy with cross-polarized detection. We find that the p-polarized near-field signal rapidly reaches a saturation level, whereas the orthogonal s-polarized channel retains a clear, layer-dependent contrast. Theoretical modeling shows that this contrast arises from the in-plane reflection coefficient (<i>r</i>_<i>s</i>), which increases approximately linearly with the conductivity of graphene in the high-<i>q</i> regime. Together, our results clarify how p- and s-polarized fields couple differently to the tip-sample system, establish a physical framework for polarization-dependent terahertz near-field responses, and point to multidimensional nanoscopic detection schemes for anisotropic materials.