Strong Purcell Effect for Terahertz Magnetic Dipole Emission with Spoof Plasmonic Structure

The magnetic Purcell effect is usually described as a modification of the magnetic dipole emission with a resonator. In an optical spectrum, various metallic and dielectric structures have been proposed to enhance the magnetic dipole emission. However, the enhancement of magnetic dipole emission by a well-designed structure has not been extensively investigated in the terahertz spectrum. Here, we propose a spoof plasmonic structure to enhance strongly the magnetic dipole emission by controlling the electromagnetic environment in the terahertz spectrum. The spoof plasmonic structure with deep-subwavelength scale is designed by periodically inserting metallic strips into a hollow silicon cylinder to obtain the “hot spot” of the localized magnetic field in the structural hollow. The resonant frequency and intensity of the magnetic dipole mode supported in this structure can be tuned freely by tailoring the structural parameters. In this context, we investigate the enhancement of a magnetic dipole emission by putting a magnetic dipole at the hollow of the spoof plasmonic structure. The results indicate that the Purcell factor can be more than 103 for a magnetic dipole emission, which is 1 order of magnitude larger than the hollow bare silicon cylinder case. We furthermore investigate the dependence of the Purcell factor on the structural parameters. The spoof plasmonic structure provides the unique ability to enhance the emission from terahertz magnetic dipoles, opening new avenues for novel magnetic light-matter interactions in the terahertz region.