Steering Smith-Purcell radiation angle in a fixed frequency by the Fano-resonant metasurface
Steering Smith-Purcell radiation angle in a fixed frequency by the Fano-resonant metasurface
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DOI：
10.1364/oe.434580
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发表时间：
2021-08-16
期刊：
影响因子：
3.8
通讯作者：
Liu, Wenxin
中科院分区：
文献类型：
--
作者：
Fu, Tao;Wang, Daofan;Liu, Wenxin
Smith-Purcell辐射（SPR）是一种电磁波辐射，当高能电子束非常接近平行于直纹光学衍射光栅的表面时发生。不同的电子速度在光栅的上下空间产生不同频率的辐射波，满足SPR关系。在这项研究中，Fano谐振超颖表面被提出来转向的SPR波在固定的谐振频率，通过改变电子束的速度，而不改变几何参数或添加额外的耦合结构。利用坡印亭矢量的积分，得到最大发射功率始终位于谐振频率处。在441 GHz处，相对辐射效率最高可达91%，当SPR方向接近垂直时，由于高透射率，效率曲线出现一个凹陷。在太赫兹频率下，无论是解析计算还是PIC（particle-in-cell of CST）模拟，通过改变电子束的速度从0.6c到0.95c，都可以使辐射角从65 °转向107 °，其中c是真空中的光速。此外，Fano共振之间的磁性模式和环形模式的破坏性干扰显示了在一个固定的频率转向SPR的基本物理。我们的研究表明，所提出的结构可以产生方向可调的太赫兹辐射波在谐振频率通过改变电子束的速度，这是有希望的各种应用在紧凑，可调谐，高功率毫米波和太赫兹波辐射源。(C)根据OSA开放获取出版协议的条款，2021年美国光学学会
Smith-Purcell radiation (SPR) is a kind of electromagnetic wave radiation that happens when an energetic beam of electrons passes very closely parallel to the surface of a ruled optical diffraction grating. The frequency of radiation waves varies in the upper and lower space of the grating for different electron velocity, satisfying the SPR relationship. In this study, a Fano-resonant metasurface was proposed to steer the direction of the SPR waves at the fixed resonant frequency by changing the velocity of the electron beam without varying the geometric parameters or adding extra coupling structure. The maximum emission power always locates at the resonant frequency by utilizing the integration of the Poynting vector. The relative radiated efficiency can reach to a maximum value of 91% at the frequency of 441 GHz and the efficiency curve has a dip when the direction of SPR is nearly vertical due to the high transmission. There is a great consistence of steering radiation angle from 65 degrees to 107 degrees by altering the velocity of electron beam from 0.6c to 0.95c both in analytical calculation and PIC (particle-in-cell of CST) simulation at terahertz frequencies, where c is the speed of light in vacuum. Furthermore, the destructive interference of Fano resonance between the magnetic mode and the toroidal mode shows the underlying physics of steering SPR in a fixed frequency. Our study indicates that the proposed structure can produce direction-tunable THz radiation waves at resonant frequency by varying the velocity of the electron beam, which is promising for various applications in a compact, tunable, high power millimeter wave and THz wave radiation sources. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement