Sub-wavelength Imaging of Terahertz Surface Currents with Aperture-type Near-field Microscopy

Ms. Sarah Norman1, Dr. James Seddon1, Dr. Yuezhen Lu1, Dr. Lucy Hale2, Dr. Abdullah Zaman3, Dr. Sadhvikas Addamane4,5, Prof. Igal Brener4,5, Dr. Riccardo Degl'Innocenti6, Prof. Oleg Mitrofanov1,4
1University College London, London, United Kingdom. 2ETH Zurich, Zurich, Switzerland. 3Lancaster University, Lancaster, United Kingdom. 4Center for Integrated Nanotechnologies, Albuquerque, USA. 5Sandia National Laboratories, Albuquerque, USA. 6Queen Mary University of London, London, United Kingdom


Terahertz (THz) near-field imaging and spectroscopy have offered valuable insights, particularly in studies of THz plasmons in emerging materials, resonators and metasurfaces. However, mapping THz surface currents so far has been beyond the reach of near-field techniques. Here, we demonstrate the capability of aperture-type scanning near-field microscopy (a-SNOM) for non-contact imaging of THz surface currents in subwavelength size resonators. Observed subwavelength-size current patterns and their dynamics reveal several excited modes in the resonator and their interplay, while THz time-domain spectroscopy analysis shows their spectral properties. This THz near-field technique can offer further insight in investigations of subwavelength resonators and metasurfaces with complex plasmonic states.