Dual non-diffractive terahertz beam generators based on all-dielectric metasurface
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RESEARCH ARTICLE
Dual non-diffractive terahertz beam generators based on all-dielectric metasurface Chunyu LIU1, Yanfeng LI (✉)1, Xi FENG1,2, Xixiang ZHANG2, Jiaguang HAN1, Weili ZHANG3 1 Center for Terahertz Waves, College of Precision Instrument and Optoelectronics Engineering, Key Laboratory of Optoelectronics Information and Technology (Ministry of Education of China), Tianjin University, Tianjin 300072, China 2 Physical Science and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia 3 School of Electrical and Computer Engineering, Oklahoma State University, Stillwater, OK 74078, USA
© Higher Education Press 2020
Abstract The applications of terahertz (THz) technology can be greatly extended using non-diffractive beams with unique field distributions and non-diffractive transmission characteristics. Here, we design and experimentally demonstrate a set of dual non-diffractive THz beam generators based on an all-dielectric metasurface. Two kinds of non-diffractive beams with dramatically opposite focusing properties, Bessel beam and abruptly autofocusing (AAF) beam, are considered. A Bessel beam with longdistance non-diffractive characteristics and an AAF beam with low energy during transmission and abruptly increased energy near the focus are generated for x- and y-polarized incident waves, respectively. These two kinds of beams are characterized and the results agree well with simulations. In addition, we show numerically that these two kinds of beams can also carry orbital angular momentum by further imposing proper angular phases in the design. We believe that these metasurface-based beam generators have great potential use in THz imaging, communications, non-destructive evaluation, and many other fields. Keywords terahertz (THz) wave, all-dielectric metasurface, Bessel beam, abruptly autofocusing (AAF) beam, vortex beam
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Introduction
Terahertz (1 THz = 1012 Hz) waves usually refer to the electromagnetic waves with a frequency in the range of 0.1–10 THz, which is a band between far-infrared light and microwaves. With the development of generation [1–3] and detection techniques [4], more research now focuses Received September 5, 2020; accepted November 1, 2020 E-mail: [email protected]
on the applications of THz waves [5,6] and the development of THz functional devices [7–9]. THz waves have a low photon energy and are transparent to non-polar and non-metallic materials, and many molecules have rotational and low-vibrational lines in the THz band, so that THz waves can be used in spectroscopy and imaging [5,6,10], non-destructive testing [11], chemical analysis [12], communications [13], and many other fields. Gaussian beams are subject to diffraction, which limits their applications in fields like optical tweezers, optical imaging, laser fabrication. The emergence of diffractionfree beams like Bessel beams [14] and Airy beams [15– 17], have greatly overcome this limitation. Bessel beams are characterized by a propagation-invariant intensity distribu
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