Weihao Liu

Numerical analysis of electron-induced surface plasmon excitation using the FDTD method

The electron-induced surface plasmon excitation is investigated using the finite-difference time-domain (FDTD) method. The frequency-dependent dielectric function of metal is approximated by the Drude model and implemented by the auxiliary difference equation (ADE) method. The interaction between electromagnetic fields and electrons is simulated by the electromagnetic particle-in-cell (PIC) method. The fundamental physics of the surface plasmon excitation on a silver surface by an electron bunch is well presented. The dispersion curve of surface plasmons (SPs) in the metal is obtained through a series of simulations. Some characteristic features of the excited SPs and important length scales are observed, and the influence of SPs on the electron bunch is considered. The numerical results agree well with the analytical and experimental results in the literature.

Free electron terahertz wave radiation source with two-section periodical waveguide structures

We analyze a free electron terahertz wave radiation source with two-section periodical waveguide structure (PWS), where the first section (section-I) is used to pre-modulate the electron beam and the second section (section-II) is for terahertz wave generation. By means of theoretical analysis and numerical simulations, we demonstrate that the starting current density of the beam-wave interaction in section-II can be significantly reduced provided that the operation frequency is the harmonic of electron beam’s pre-modulation frequency. This kind of source can generate relatively high power terahertz wave radiation but only need moderate beam current density. And it may have great potential application in developing the compact and high power terahertz wave radiation source.

Diffraction radiation of a sub-wavelength hole array with dielectric medium loading

In this paper we show that under the excitation of a line current of electron beam, a dielectric medium loading in the lower half-space of a sub-wavelength hole array brings essential changes to the diffraction radiation. In the lower half-space, the surface wave becomes a radiation wave. The fundamental space harmonic is transformed into Cherenkov radiation with unique characteristics and the first negative space harmonic is converted into a radiation wave with the angle of Smith–Purcell radiation. Consequently, in the lower half-space interference happens due to these two kinds of diffraction radiation. The results of numerical calculations based on analytical theory agree well with that obtained by computer simulations. The mechanism may have good potential applications in modern physics.

Theoretical investigation of a terahertz transmission line in bipolar coordinate system

It has been demonstrated that the dual-wire waveguide (DWW) can be used in terahertz (THz) frequency regime with many advantages. However, the existent research approaches for the DWW are based on the electrostatic theory. In this paper, making use of the bipolar coordinate system (BCS), a rigorous analytical theory of DWW is worked out, and some important physical and optical characters of DWW including the rotating behavior etc. are revealed, the equivalent impendence and the ohmic loss for the gold DWW are calculated. An eigenvalue problem is presented from the point of view of Mathematical-Physics for TE and TM modes. The obtained results will help get a deep-going understanding of DWW and explore its application in high frequency range including THz.

Investigations on a nano-scale periodical waveguide structure taking surface plasmon polaritons into consideration

Detailed theoretical analysis and computer simulations on the electromagnetic characteristics of a nano-scale periodical waveguide structure, taking surface plasmon polaritons (SPPs) into consideration, are carried out in this paper. The results show that SPPs will significantly influence the electromagnetic characteristics of the structure. When the operation frequency is in a certain band?the ?radial confinement band?, neither radial surface plasmon waves nor guided waves, which both will lead to radial energy loss, can be excited in the structure. And the electromagnetic waves are completely confined within the longitudinal waveguide and propagate along it with little attenuation. The radial energy loss is then significantly reduced. These results are of great significance not only for increasing the efficiency of the radiation sources based on the nano-scale periodical waveguide structure but also for the development of high-efficiency waveguides and wide-band filters in the infrared and visible light regimes.