Zhong Renbin

Surface plasmon wave propagation along single metal wire

Recently, the single metal wire (SW) has become attractive for its potential applications in the terahertz and higher frequency range. However, as the most simple and typical surface plasmon polariton (SPP) transmission line, its study seems far from enough. Many important transmission behaviours have not been explained satisfactorily from the viewpoint of physics. In this paper, making use of the modified Drude model (MDM) based on the Sommerfeld theory, the transmission behaviours of SPPs along SW are systemically investigated theoretically. Some important physical phenomena such as the mode transformation, the lifetime of the radiative mode and the resonance frequency are revealed, and their mechanisms are explored. The results obtained in the paper will facilitate a general understanding of the features and the physical essence of the SPP transmission, not only for SW itself but also for other SPP transmission lines.

Tunable terahertz radiation from arbitrary profile dielectric grating coated with graphene excited by an electron beam

In this paper, the enhanced terahertz radiation transformed from surface plasmon polaritons, excited by a uniformly moving electron bunch, in a structure consisting of a monolayer graphene supported on a dielectric grating with arbitrary profile is investigated. The results show that the grating profile has significant influence on the dispersion curves and radiation characteristics including radiation frequency and intensity. The dependence of dispersion and radiation characteristics on the grating shape for both the symmetric and asymmetric gratings is studied in detail. Moreover, we find that, for an asymmetric grating with certain profile, there exist two different diffraction types, and one of the two types can provide higher radiation intensity comparing to the other one. These results will definitely facilitate the practical application in developing a room-temperature, tunable, coherent and miniature terahertz radiation source.

Enhancement of Smith—Purcell radiation with surface-plasmon excitation

With the aid of a three-dimensional particle-in-cell code simulation, the enhancement of Smith—Purcell radiation with a surface-plasmon mode excited by a single electron bunch and by a premodulated electron beam is considered in the paper. In the simulation, the model is a grating covered by Ag film. The results demonstrate that when the surface-plasmon mode is excited by a single electron bunch, the maximum radiation occurs at an observation angle depending on the surface-plasmon frequency, and the radiation power can be enhanced more than ten times. And for pre-bunched electron beam excitation, when one of the harmonics of the bunching frequency is resonant with that of the surface-plasmon mode, the radiation power is twenty times more than that from a perfectly conducting grating excited by the same premodulated electron beam.

Terahertz radiation from interaction between an electron beam and a planar surface plasmon structure

The possibility of an electron beam exciting surface plasmons in conducting metal is discussed in this paper. A planar perfect-structure with subwavelength holes is proposed. The phenomenon that mimicking surface plasmon waves can be excited and amplified by an electron beam is proved theoretically and numerically. The mechanism of transmission through a subwavelength hole array is exploited to enhance the interaction between the electron beam and the mimicking surface plasmons.

The study on the coaxial gyrotron with two electron beams

To meet the needs of the ITER program, the coaxial cavity gyrotron with very high mode, like TE/sub 43.19/, operating at 170GHz with 2MW CW output power was proposed and studied. Since there are outer and inner conducting cylinders with the same electric potential, and the high mode makes the size of the cavity large enough. The high mode coaxial cavity structure, therefore, enables the suggestion of the two-electron beam coaxial gyrotron (TBCG). This paper deals with the coaxial gyrotron with two-electron beam, and the computer calculations have been carried out. The detailed comparison of the performances of the two-beam gyrotron with that of one-beam is given as well in the paper. The study on the two beam coaxial gyrotron shows that the two beam gyrotron may performance quite well, for example, the TBCG may enhance the higher output power for the two beams may provide higher electric current; and it may improve the mode competition for working at very high mode with potential V=90kV. Detailed analysis and computer simulations for all mention are given in the paper.

Coherent and tunable radiation with power enhancement from surface plasmon polaritons

Surface plasmon polaritons excited by an electron beam can be transformed into coherent and tunable light radiation waves with power enhancement in the simple structure of a metal film with a dielectric medium loading. In this paper, the process of the radiation transformation of this radiation, and the dependencies of the radiation characteristics on the parameters of the structure and the electron beam are studied in detail. The radiation power enhancement is greatly influenced by the beam energy and the film thickness in the infrared to ultraviolet frequency region. Up to 122 times radiation power enhancement and 6.5% radiation frequency tuning band can be obtained by optimizing the beam energy and the parameters of the film.

Terahertz radiation generation with a special kind of mimicking surface plasmon wave structure

A special kind of mimicking surface plasmon wave structure is proposed and studied, and the electron beam-wave interaction to generate THz radiation is explored in the paper. Since the mimicking surface plasmon wave (MSP) is slow wave, in physics, it enables the beam-wave interactions and may open an alternate way of the combination of electronics and photonics for the development of THz radiation sources. The results of both theoretical analysis and computer simulation are given. It demonstrates that up to 16% modulation depth may be obtained.

THz Coherent Vavilov-Cherenkov Radiation in a Special 3-Mirror Cavity

The study of THz radiation sources is one of the most attractive and important topics in modern science and technology. Theoretical study and computer simulation of the THz Vavilov-Cherenkov radiation (VCR) in a 3-mirror cavity are presented in the paper. The 3-mirror cavity was specifically developed based on the Fabry-Perot cavity, it may greatly increase the output power and improve the coherence of the radiation through collecting the emission of the radiation in the entire solid angle of the radiation direction at a resonant mode of the cavity. Under coherent conditions the VCR of electron bunches excites one of the resonant modes in the cavity. For 4.41 dielectric permittivity and 180 keV electron beam, the VCR at 0.8 THz was obtained.

The Study of Coaxial Gyrotron with Two Beams

Results of the theoretical analysis and computer simulations for the coaxial gyrotron with two electron beams (CGTB) are given. It is shown that CGTB has a number of advantages, the output power can be doubled and the mode competition can be significantly improved, the CGTB can also operates simultaneously at two modes with different cyclotron harmonics.

Theoretical and experimental study of a THz cavity

A three-mirror THz cavity has been presented based on the Fabry-Perot cavity. Theoretical and experimental studies on this cavity have been carried out together with the computer simulation by means of MAGIC code. A very good agreement has been achieved among the theoretical calculations, the computer simulation and the experimental results. All these show that a good THz cavity has been developed. Some possible applications of the cavity in the THz radiation sources have also been given in the paper.