Abstract

Terahertz (THz) vortex beams carrying orbital angular momentum (OAM) with high purity and tunable topological charge (TC) will undoubtedly bring extraordinary capacities for advanced imaging or communication systems. We propose a convenient and efficient method to generate a tunable and broadband vortex beam that is excited by superradiant Smith-Purcell radiation (SSPR) on a helical grating. This scheme fully explores the advantages of natural broadband evanescent wave carried by the electron beam and the Bloch's theorem regulated helical periodic systems. An explicit relation is established between the index of the spatial harmonic wave on the grating and the topological charge of the vortex beam. The electron energy in the SSPR can be customized to ignite the specific spatial harmonics and manipulate the OAM beam, accordingly. The separated radiation region also promises the high purity of the OAM spectrum. The harmonic excitation reduces the communality between the wavelength and the device size and alleviates the difficulty of device fabrication in the THz band. The proposed vortex scheme can not only be handily scaled to microwave and mid-infrared regions, but also bring possibilities to applications based on compact tunable vortex beam sources.

Plasmonic vortex beam emitter

Zi-Wen Zhang, Yu-Lu Lei, Juan-Feng Zhu, and Chao-Hai Du
Photon. Res. 11(10) 1723-1732 (2023)

Measuring the topological charge of terahertz vortex beams with a focal hyperbolic lens

Yongqiang Yang, Liting Niu, Zhengang Yang, and Jinsong Liu
Appl. Opt. 59(15) 4685-4691 (2020)

Smith–Purcell radiation from helical grating to generate wideband vortex beams

Juan-Feng Zhu, Chao-Hai Du, Zi-Wen Zhang, Pun-Kun Liu, Liang Zhang, and Adrian W. Cross
Opt. Lett. 46(18) 4682-4685 (2021)

Vortex Smith–Purcell radiation generation with holographic grating

Mengxuan Wang, Fang Liu, Yuechai Lin, Kaiyu Cui, Xue Feng, Wei Zhang, and Yidong Huang
Photon. Res. 8(8) 1309-1315 (2020)

Orbital angular momentum and topological charge of a multi-vortex Gaussian beam

Alexey A. Kovalev, Victor V. Kotlyar, and Alexey P. Porfirev
J. Opt. Soc. Am. A 37(11) 1740-1747 (2020)