Near-Field Spectroscopy of Individual Asymmetric Split-Ring Terahertz Resonators

Metamaterial resonators have become an efficient andversatileplatform in the terahertz frequency range, finding applications inintegrated optical devices, such as active modulators and detectors,and in fundamental research, e.g., ultrastrong light-matterinvestigations. Despite their growing use, characterization of modessupported by these subwavelength elements has proven to be challengingand it still relies on indirect observation of the collective far-fieldtransmission/reflection properties of resonator arrays. Here, we presenta broadband time-domain spectroscopic investigation of individualmetamaterial resonators via a THz aperture scanning near-field microscope(a-SNOM). The time-domain a-SNOM allows the mapping and quantitativeanalysis of strongly confined modes supported by the resonators. Inparticular, a cross-polarized configuration presented here allowsan investigation of weakly radiative modes. These results hold greatpotential to advance future metamaterial-based optoelectronic platformsfor fundamental research in THz photonics.

Automated summary

Metamaterial resonators in the terahertz frequency range have proved to be efficient and versatile platforms with applications in integrated optical devices and fundamental research. However, characterizing the modes supported by these subwavelength elements has been challenging, relying on indirect observation of collective far-field transmission/reflection properties of arrays. In this study, we present a broadband time-domain spectroscopic investigation of individual metamaterial resonators using a THz aperture scanning near-field microscope (a-SNOM). The results allow mapping and quantitative analysis of confined modes supported by the resonators, including weakly radiative modes.