Mapping the coupling between a photo-induced local dipole and the eigenmodes of a terahertz metamaterial

Abstract

We demonstrate that eigenmodes of a metamaterial structure at terahertz (THz) frequencies can be excited by photo-generation of localized transient dipoles in the semiconductor substrate. We apply this technique to map the coupling of these dipoles to the resonator's near-field. The characteristic metamaterial resonances appear as peaks in the spectrum of the THz radiation emitted from the resonant structures into the far-field. Recording two-dimensional THz emission maps allows us to reproduce the frequency-dependent spatial profiles of the metamaterial's eigenmodes.

Imaging of THz Photonic Modes by Scattering Scanning Near-Field Optical Microscopy

“…However, as for the LSA, the simulation does not account for the dark area. Similar design of SRRs have been already studied by other THz microscopy techniques at larger scale [52,53,54,55,56,57,58,59], but to the best of our knowledge, this feature was not previously reported and may only manifest in THz s-SNOM.…”

“…A similar design of SRRs has been already studied by other THz microscopy techniques at a larger scale [43][44][45][46][47][48]50 and do not exhibit N-S asymmetry. At a smaller scale, in the work of Acuna et al, 49 the authors used a technique similar to s-SNOM on SRRs but did not report this effect.…”

“…SRRs concentrate electric field in their gap when receiving electromagnetic waves matching their inductor-capacitor resonance. Various designs of THz SRRs and complementary SRRs have been studied at larger scale with other imaging techniques, i.e., with PC and EO detectors [52,53,54,55], emission microscopy [56], tapered dipole antenna sensor [57], apertureless microscopy [58] and real-time THz microscopy [59]. Meanwhile, to the best of our knowledge, THz spiral antennas were not imaged in the NF so far.…”

“…Various designs of THz SRRs and complementary SRRs have been studied at a larger scale with other imaging techniques, i.e. , with PC and EO detectors, − emission microscopy, tapered dipole antenna sensor, apertureless microscopy, and real-time THz microscopy, but existing literature on s-SNOM imaging of SRRs remains limited . Indeed, despite vivid interest in the applications of THz s-SNOM, so far, to the best of our knowledge, only two studies focused on photonic resonators, , and similarly to shape-dependent contrast, interpretation of the recorded features is a recent subject of matter in the field of THz studies.…”