High‐Q Metallic Fano Metamaterial for Highly Efficient Cerenkov Lasing

Abstract

development of such CR-based applications is limited by thermal and dielectric breakdown issues. [3,4] Another limitation is that, due to the velocity threshold, large facilities are required to generate highly energetic particles. These limitations restrict the upper and lower size and performance boundaries in vital applications. Nowadays, metallic metamaterial devices have been proposed, which overcome the limitations of conventional Cerenkov devices to realize reversed CR from the negative-refractive index, [5] the ultralow threshold of kinetic energy in hyperbolic metamaterials, [6] and various metallic metamaterials comprised of subwavelength slits. [7][8][9] However, the realization of a high quality factor (Q) is still an outstanding roadblock for practical Cerenkov devices. Previous works on Cerenkov lasing (CL) using mirrors were limited by a lower electron beam impedance due to the interaction device and the radio-frequency (RF) coupling mechanism. [4,10] Here, to achieve a high Q for highly efficient CL, we focus on maximally trapping the electromagnetic Cerenkov radiation wave to extend its interaction with the electron beam and on controlling the radiation damping, as has been described in Rayleigh scattering to maximize the efficiency of CL. In this paper, we demonstrate that the interplay between an extremely low group velocity from the infinite transverse permittivity of the anisotropic metamaterials and the subradiant A high-quality-factor (high-Q) metallic Fano metamaterial is demonstrated both experimentally and theoretically. This material is suitable for highly efficient Cerenkov lasing in which subwavelength metallic slits are arranged to form asymmetric unit cells. In contrast to conventional dielectric Cerenkov or Smith-Purcell devices, in the proposed device, convection electrons traverse the high-Q metallic metamaterial. The interplay between an extremely low group velocity from the infinite transverse permittivity of the anisotropic metamaterial and the subradiant damping from a Fano-type slit mode is shown to be responsible for the high-Q value, which is measured to be unprecedented at 700. The resulting improvement in the Cerenkov lasing efficiency is estimated to be more than two orders of magnitude using a particle-in-cell simulation.

Free-Electron-Driven Multi-Frequency Terahertz Radiation on a Super-Grating Structure

“…The distance between the free electron and the grating surface is d g . As a form of Fano metamaterial, the super-grating has been widely studied in the past decades, and its high-Q property is promising for various applications in VEDs [23], [24]. However, the multi-frequency radiation characteristic has not been explored.…”

“…Whereas, the Smith-Purcell radiation (SPR) has been expected as a promising candidate [20]- [22]. The SPR-like spatial radiation are investigated in a high-Q Fano grating, and the radiation characteristics strongly depends on the electromagnetic resonance in the structure [23]. Despite the spatial radiation can be achieved, the multi-frequency radiation has not been extensively investigated.…”

Ultra-High Quality Factor Resonances in a Pinwheel-Shaped All-Dielectric Metasurface Based on Bound States in the Continuum

“…Q-factor is a crucial parameter to assess the performance of Fano resonance. At present, Fano resonance with a high Q-factor has been widely used in the field of optics, such as nonlinear optics [4,5], high performance sensor [6][7][8], and laser [9,10]. But the metalbased plasma nanostructures such as free electron oscillation causes large ohmic loss, which leads to wide resonant spectral lines.…”

Observation of Fano-like resonance in dual-blade shaped gold nanostructures

“…Metamaterials exhibiting optical Fano resonances have recently attracted intense attention owing to their promising applications in lasing [1,2], filtering [3], optical switching [4], optical sensing [5][6][7], light trapping [8,9], luminescence [10], optical chirality [11], and nonlinear and slow-light optical devices [12][13][14][15]. The emerging features of Fano resonance originate from its ultra-sharp spectral feature and extreme field localization.…”