Abstract-Huge field enhancement and high transmittance enabled by terahertz bow-tie aperture arrays: a simulation study

Xupeng Zhu, Shi Zhang, Huimin Shi, Mengjie Zheng, Yasi Wang, Shuwen Xue, Jun Quan, Jun Zhang, and Huigao Duan

 (a) The charge distribution of a BTAAs unit cell at the feature frequencies of 1.13 THz and 1.46 THz when S = 0.04 µm, respectively. Top surface: the interface between the Au film and the vacuum. Bottom surface: the interface between the Au film and the adhesive substrate. (b) The field distribution around the feature gap size of S = 0.04 µm. Blue solid line: the line field distribution on the x-axis (y = 0). Red solid line: the line field distribution on the y-axis (x = 0).

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-4-5851

Sub-wavelength aperture arrays featuring small gaps have an extraordinary significance in enhancing the interactions of terahertz (THz) waves with matters. But it is difficult to obtain large light-substance interaction enhancement and high optical response signal detection capabilities at the same time. Here, we propose a simple terahertz bow-tie aperture arrays structure with a large electric field enhancement factor and high transmittance at the same time. The field enhancement factor can reach a high value of 1.9×104 and the transmission coefficient of around 0.8 (the corresponding normalized-to-area transmittance is about 14.3) at 0.04 µm feature gap simultaneously. The systematic simulation results show that the designed structure can enhance the intensity of electromagnetic hotspot by continuously reducing the feature gap size without affecting the intensity of the transmittance. We also visually displayed the significant advantages of extremely strong electromagnetic hot spots in local terahertz refractive index detection, which provides a potential platform and simple strategy for enhanced THz spectral detection.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Saturated absorption of different layered Bi2Se3 films in the resonance zone [Invited]

Jun Zhang, Tian Jiang, Tong Zhou, Hao Ouyang, Chenxi Zhang, Zheng Xin, Zhenyu Wang, and Xiang’ai Cheng

http://65.202.222.105/prj/abstract.cfm?uri=prj-6-10-C8

Here, we used the micro P-scan method to investigate the saturated absorption (SA) of different layered Bi2Se3${\mathrm{Bi}}_2{\mathrm{Se}}_3$ continuous films. Through resonance excitation, first, we studied the influence of the second surface state (SS) on SA. The second SS resonance excitation (∼2.07  eV$\sim 2.07\mathrm{eV}$) resulted in a free carrier cross section that was 4 orders of magnitude larger than usual. At the same time, we found that the fast relaxation process of the massless Dirac electrons is much shorter than that of electrons in bulk states. Moreover, the second SS excitation resonance reduced the saturation intensity. Second, we studied the effect of the thickness on the SA properties of materials. The results showed that the saturation intensity was positively correlated to the thickness, the same as the modulation depth, and the thicker the Bi2Se3${\mathrm{Bi}}_2{\mathrm{Se}}_3$ film was, the less the second SS would influence it. This work demonstrated that by using Bi2Se3${\mathrm{Bi}}_2{\mathrm{Se}}_3$ as a saturable absorber through changing the thickness or excitation wavelength, a controllable SA could be achieved.

© 2018 Chinese Laser Press

Abstract-Graphene-based tunable Imbert–Fedorov shifts and orbital angular momentum sidebands for reflected vortex beams in the terahertz region

Linqing Zhuo, Wenjin Long, Mengjiang Jiang, Wenguo Zhu, Heyuan Guan, Jieyuan Tang, Jianhui Yu, Huihui Lu, Jun Zhang, and Zhe Chen

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-43-12-2823

Upon reflection, a light beam embedded with 𝑚$m$-order orbital angular momentum (OAM) will undergo the Imbert–Fedorov (IF) shift, which induces OAM sidebands. The energies of the neighboring {−𝑚−1}$\{-m-1\}$ and {−𝑚+1}$\{-m+1\}$ sideband modes of the reflected beam are always equal. Controllable OAM sidebands are theoretically achieved by introducing a monolayer graphene in a three-layer structure composed of air, hexagonal boron nitride, and metal. By modulating the Fermi energy of graphene, the OAM-dependent IF shift can be tuned from positive to negative values, and the OAM sideband modes can be suppressed or enhanced, since the reflectivity for perpendicular and parallel polarizations vary with the Fermi energy. These findings provide an alternative method for the control of optical OAM in the terahertz region.

© 2018 Optical Society of America