Mediated coupling of surface plasmon polaritons by a moving electron beam

The mediated coupling of surface plasmon polaritons (SPPs) by a parallel moving electron beam is demonstrated in this paper. The theoretical analysis shows that the electron beam excited spoof surface plasmon polaritons (SSPs) on the grating placed above the metal films play the role as the excitation source in the mediated coupling. The numerical calculations and particle-in-cell simulations demonstrate the significant advantages of the SSPs mediately coupled SPPs in contrast with that coupled by the parallel moving electron beam directly. The photo density of the mediately coupled SPPs reaches up to 10 6 per cm 2 for the electron beam with the charge density 100 nC/cm, which is two orders of magnitude larger than that of the directly coupled SPPs. The tuning band of the mediately coupled SPPs reaches up to 9% for the beam energy ranging from 10 keV to 30 keV, while it almost cannot be tuned for the direct coupling. The lifetime of the mediately coupled SPP s, which reaches up to hundreds of femtoseconds, is also much longer. Accordingly, the mediated coupling may bring great significances for the applications of SPPs

Surface plasmon polaritons light radiation source with asymmetrical structure

An asymmetrical surface plasmon polaritons (SPPs) light radiation source with double metal films (SPLRD) is presented and studied. SPPs modes can be excited on the double metal films by a parallel traveling electron beam and then transformed into enhanced Cherenkov radiation in the substrate. Tunable dual-frequency radiation ranging from infrared to ultraviolet can be realized. In comparison with a single-metal-film structure, the efficiency, tunability, and output power density of the SPLRD are greatly increased, with up to eight times higher radiation power intensity being achievable. The radiation performance of a cylindrical SPLRD is enhanced to an even greater extent, with reductions in the required exciting electron-beam energy and the dielectric substrate permittivity. These novel properties due to the asymmetry of the structure and the SPPs excitation pattern are significant for furthering the understanding of electron beam–SPPs interaction and for the development of efficient wideband light radiation sources

Coherent terahertz Smith-Purcell radiation from Dirac semimetals grating with very deep and narrow slits

We demonstrate a physical mechanism of multicolor coherent terahertz (THz) Smith-Purcell radiation from surface plasmon polaritons (SPPs). In Dirac semimetals gratings with very deep and narrow slits, two types of SPP modes, the cavity and ordinary SPP modes, can be excited by fast electrons under different excitation conditions and then diffracted into radiation in specific directions. The radiation intensity is remarkably enhanced when SPPs are excited, and frequencies can be widely tuned by adjusting the parameters of grating and electrons. Our findings could provide a promising way for developing room temperature, coherent, tunable, directional, and intense THz radiation sources

Graphene loaded double ridge plasmon Terahertz waveguide

In this paper, a single-mode graphene loaded double ridge plasmon waveguide (GDRW) with long propagation length and strong mode confinement is proposed. The characteristics of the guided modes are investigated in detail, and tunable single-mode transmission with good performance can be realized either by changing the Fermi energy level or by optimizing the key structural parameters. High figures of merit and much lower crosstalk are obtained due to the dramatically suppressed interference between two parallel placed GDRWs, enabling thereby more tightly stacking in terahertz integrated circuits. Further investigation on fabrication errors, such as the horizontal misalignment of the two symmetric ridges, fabrication distortion of rectangular ridges, and variation of ridge tip curvature radius, indicates that the proposed structure has enough fabrication error tolerance. The results are greatly expected to facilitate the application of high-density terahertz integrated circuits

An Approach to Polygonal Approximation of Digital Curves Based on Discrete Particle Swarm Algorithm

An approach to polygonal approximation of regular digital curves based on PSO algorithm is presented. In this paper, each particle corresponds to a candidate solution to the polygonal approximation problem, which is represented as a binary vector. The offset error of centroid between the original curve and the approximation polygon, and the variance of distance error for each approximation segment are adopted in the fitness function to evaluate the feasibility degree of the candidate solution. The sigmoid function of iteration times is used as the acceleration factors instead of the constant factors to improve the global searching characteristics. Experimental results show that the proposed approach can get suitable approximation results for preserving the features of original curves

Coherent and tunable terahertz radiation from graphene surface plasmon polaritons excited by an electron beam

Although surface plasmon polaritons (SPPs) resonance in graphene can be tuned in the terahertz regime, transforming such SPPs into coherent terahertz radiation has not been achieved. Here, we propose a graphene-based coherent terahertz radiation source with greatly enhanced intensity. The radiation works at room temperature, it is tunable and can cover the whole terahertz regime. The radiation intensity generated with this method is 400 times stronger than that from SPPs at a conventional dielectric or semiconducting surface and is comparable to that from the most advanced photonics source such as a quantum cascade laser. The physical mechanism for this strong radiation is presented. The phase diagrams defining the parameters range for the occurrence of radiation is also shown