Coherent terahertz microscopy of modal field distributions in micro-resonators

Near-field microscopy techniques operating in the terahertz (THz) frequency band offer tantalizing possibility of visualizing with nanometric resolution localized THz fields supported by individual resonators, micro-structured surfaces, and metamaterials. Such capabilities promise to underpin future development characterization a wide range devices, including emitters, detectors, optoelectronic modulators, sensors, novel optical components. In this work, we report scattering-type scanning near-field using THz-frequency quantum cascade laser (QCL) probe coherently field micro-resonator structures. Our technique demonstrates deep sub-wavelength mapping distribution associated in-plane resonator modes plasmonic dipole antennas split ring By exploiting electronic tuning QCL conjunction coherent self-mixing effect these lasers, are able resolve both magnitude phase out-of-plane field. We, furthermore, show that elliptically polarized state can be exploited for simultaneous excitation measurement resonances structures while suppressing otherwise dominant signal arising from local material permittivity.