Surface waves (SWs) are of great importance in terahertz (THz) photonics applications due to their subwavelength properties. Hence, it is crucial to develop surface wavefront shaping techniques, which is urgent in modern information technologies. In this paper, a new scheme is proposed to realize SW excitation and spin-decoupled wavefront shaping with an ultracompact planar meta-device working in the THz range. The meta-device is composed of two parts: meta-atoms (in the center) and plasmonic metals (on the left and right sides). By carefully setting the geometry size and rotation angle of each meta-atom, the encoded spin-decoupled phase distributions for both left circularly polarized (LCP) and right circularly polarized (RCP) incident THz waves are determined. In this way, circularly polarized (CP) incident THz waves can be converted to SWs propagating along plasmonic metals with unique wavefront profiles, i.e., Bessel and focusing profiles. Full-wave simulations and THz near-field scanning experiments were performed to verify the functionalities of the meta-device, both of which are in great agreement with theoretical predictions. Our findings may provide more solutions to design THz integrated photonic devices and systems.
Aiming at the beam-wave interaction in the helix TWTA, some of the main calculation results which were based on the loss transmission line model and kinetics equation with the particle-in-cell technic of the time-domain were shown in this paper. Comparison of the test results, it is apparent to see the two results were consistent. Secondly aiming at the nonlinear phase distortion, a result of phase length is shown in the later. The calculation result is 45 degrees which is close to the test of the institute (IECAS).
Summary form only given. In this paper, a low-voltage high-efficiency 330 GHz tunable gyrotron is investigated, which operates on the open-cavity TE 6,2 mode and employs an electron beam with voltage of 20 kV, current of 0.5A, and pitch factor of 1.5. Simulation achieves a competitive efficiency, more than 40%, under the assumption of using copper circuit wall and electron beam of 5% velocity spread. Besides, the investigation of the start-oscillation currents of the TE 6,2 and TE 1,4 modes indicates that the system is with reasonable broadband tunability.
Advances in graphene plasmonics offer numerous opportunities for enabling the design and manufacture of a variety of nanoelectronics and other exciting optical devices. However, due to the limitation of material properties, its operating frequency cannot drop to the microwave range. In this work, a new concept of microwave equivalent graphene based on the ultrathin monolayer plasmonic metasurface is proposed and demonstrated. Based on this concept, elliptical and hyperbolic dispersion can be theoretically obtained by stacking the equivalent graphene metasurfaces periodically. As proofs of the concept and method, an elliptical and an all-metal hyperbolic metamaterial are designed and numerically demonstrated. As a specified realization of the method, a practical hyperbolic metamaterial is fabricated and experimentally investigated with its validity verified by the directional propagation and photonic spin Hall effect. Furthermore, to investigate the validity of the method under extreme parameter conditions, a proof-of-concept hyperlens is designed and fabricated, with its near-field resolution of 0.05$\lambda$ experimentally verified. Based on the proposed concept, diverse optical graphene metamaterials such as focusing lens, dispersion-dependent directional couplers, and epsilon-near-zero materials can also be realized in the microwave regime.
The Institute of Electronics, Chinese Academy of Sciences (IECAS) is developing the 50MW S-band klystron for use in linear accelerators. A klystron structure of six-cavity and single output window is adopted. The first prototype was fabricated and tested, and the test results show the design of electron optics and RF system is basically successfully. This paper describes the development and status of this device including design ideas, simulation results and recent progress.
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