Zhang Yaxin

A broadband and tunable MMW–THz quasi-optical cavity

Based on the Fabry?Perot cavity, a broadband and tunable cavity is presented and investigated theoretically and experimentally. The results show that the cavity can work in the millimetre wave (MMW)?THz frequency regime. The experimental Q value is up to about 6000 at 37.5?GHz and higher than 800 at 2.54?THz. The resonant frequency of the cavity can be tuned by adjusting the distance between two mirrors, and it is capable of working at a high power. So this quasi-optical cavity may have very good potential applications in MMW?THz science and technology.

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.

Planar terahertz metamaterial with three-resonant frequencies

In this paper, we study a three-resonant metamaterial with the combination of dual-resonant and single-resonant metamaterials. We present a new method to design multi-resonant metamaterial, which has a smaller dimension than general symmetric and asymmetric multi-resonant metamaterials. Theoretical and experimental results show that the structure has three distinct absorption frequencies centering around 0.29 THz, 0.46 THz, and 0.92 THz, and that each of them corresponds to a different resonant mode. Due to the good separation of the different resonances, this design provides a unique and effective method to construct multiband terahertz devices.

Theoretical study of wave propagation along the coaxial waveguide filled with moving magnetized plasma

This paper presents detailed theoretical study on the theory of wave propagation along the coaxial waveguide filled with moving magnetized plasma (CWMMP). Making use of the Lorentz transformation and the constitutive transformation, Maxwells equations lead to the coupled non-homogeneous differential equations which govern the wave propagation in CWMMP, and then analytical solutions have been obtained. The discussion about the eigenvalues of the waves and detailed studies on the fields are carried out. It finds that the fields of the CWMMP are composed of two parts with different eigenvalues. Numerical calculations show that because of Doppler shift effect, the eigenvalues of the modes in such a case is quite different from those of the CWMMP. And a detailed discussion on the dispersion characteristic of CWMMP is presented.

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.

Electromagnetic diffraction radiation of sub-wavelength holes array excited by a point charge

The mechanism of this novel 3D diffraction radiation phenomenon is revealed. A rigorous theoretical solution is obtained for the problem of electromagnetic diffraction radiation of sub-wavelength holes array (SHA) excited by a point charge moving parallel to the one surface of SHA.