Abstract-Evanescent resonant mode for a T-shaped cavity in a terahertz parallel-plate waveguide

Kai Wang, Qing Cao, Huifang Zhang, Pengcheng Shen, and Lujing Xing

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-57-27-7967

The evanescent resonant modes are proposed for a T-shaped cavity in a terahertz (THz) parallel-plate waveguide (PPWG) to understand the essence of the resonant phenomenon. The theoretical modal field and the resonant frequency of the TE2${}_{\mathrm{}}$-like evanescent resonant mode show agreement with the simulated ones through the whole THz region. The modal field consists of three evanescent fields outside the cross region and one propagation field inside the cross region. When the TE2${}_{\mathrm{}}$-like mode is excited, the input THz wave is reflected. The resonance frequency of the TE2${}_{\mathrm{}}$-like mode depends closely on the geometrical parameters of the T-shaped cavity. In particular, the separation of the PPWG must be twice larger than the width of the groove to avoid the non-evanescent electric field in the groove. In addition, the electric field of the TE1${}_{\mathrm{}}$-like mode is localized in the T-shaped cavity. These results have potential applications in field enhancement, sensors, and filters.

© 2018 Optical Society of Americahttps://www.osapublishing.org/ao/abstract.cfm?uri=ao-57-27-7967

Abstract-Terahertz and infrared characteristic absorption spectra of aqueous glucose and fructose solutions

Chao Song, Wen-Hui Fan, Ling Ding, Xu Chen, Ze-You Chen,  Kai Wang,

https://www.nature.com/articles/s41598-018-27310-7

In this paper, the terahertz (THz) and infrared (IR) characteristic absorption spectra of aqueous glucose solutions and aqueous fructose solutions with different concentrations were measured and studied. The absorption spectra of these two molecules in solid-state and in aqueous solutions were compared and analyzed, the significant effect of molecular adjacent environment on the molecular structure and vibrational mode was revealed. In addition, the THz and IR absorption spectra of these two isomers’ aqueous solutions were also compared and explored. No obvious differences were found from their IR absorption features measured at room temperature, while their THz absorption spectra do have the differences, indicating THz characteristic absorption spectra more suitable for the detection and identification of aqueous glucose and fructose solutions. The results are helpful to understand the influence of aqueous solutions environment on the molecular structures and vibrational modes of the materials, and also provide a theoretical reference for the quantum chemical calculation of biological macromolecules.

Abstract-Broadband tunable terahertz absorber based on vanadium dioxide metamaterials

Zhengyong Song, Kai Wang, Jiawen Li, and Qing Huo Liu

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-6-7148

An active absorption device is proposed based on vanadium dioxide metamaterials. By controlling the conductivity of vanadium dioxide, resonant absorbers are designed to work at wide range of terahertz frequencies. Numerical results show that a broadband terahertz absorber with nearly 100% absorptance can be achieved, and its normalized bandwidth of 90% absorptance is 60% under normal incidence for both transverse-electric and transverse-magnetic polarizations when the conductivity of vanadium dioxide is equal to 2000 𝛺−1𝑐𝑚−1$2000{\Omega }^{-1}c{m}^{-1}$. Absorptance at peak frequencies can be continuously tuned from 30% to 100% by changing the conductivity from 10 𝛺−1𝑐𝑚−1$10{\Omega }^{-1}c{m}^{-1}$ to 2000 𝛺−1𝑐𝑚−1$2000{\Omega }^{-1}c{m}^{-1}$. Absorptance spectra analysis shows a clear independence of polarization and incident angle. The presented results may have tunable spectral applications in sensor, detector, and thermophotovoltaic device working at terahertz frequency bands.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Giant Two-Photon Absorption and Its Saturation in 2D Organic–Inorganic Perovskite

Weiwei Liu, Jun Xing, Jiaxin Zhao, Xinglin Wen,Kai Wang, Peixiang Lu, Qihua Xiong

http://onlinelibrary.wiley.com/doi/10.1002/adom.201601045/abstract

Organic–inorganic perovskites have attracted great attentions driven by exceptional progress in photovoltaics, photonics, and optoelectronics. Different from the corner sharing framework of 3D perovskite, 2D organic–inorganic perovskites possess a layered staking structure composed of alternative organic and inorganic components. Due to the inherent multi-quantum-well-like structure, it is intriguing to explore the optical properties of 2D perovskites enabled by spatial and dielectric confinement. Herein, the two-photon absorption (TPA) properties of 2D perovskite phenylethylamine lead iodide ((PEA)2PbI4) are systematically studied. The 2D perovskite exhibits a giant TPA and saturation effect under excitation of 800 nm femtosecond laser. The TPA coefficient of a (PEA)2PbI4 flake is measured to be about 211.5 cm MW−1, which is at least one order of magnitude larger than those of 3D perovskite films and some typical semiconductor nanostructures. The giant TPA can be attributed to the enhanced quantum and dielectric confinement in the organic–inorganic multi-quantum-well structure. In addition, a highly thickness-dependent TPA is observed for the 2D perovskite flakes. The result advocates a great promise of 2D organic–inorganic perovskites for nonlinear optical absorption related optoelectronic devices.

Abstract-Enhanced plasmonic nanofocusing of terahertz waves in tapered graphene multilayers

Weiwei Liu, Bing Wang, Shaolin Ke, Chengzhi Qin, Hua Long, Kai Wang, and Peixiang Lu
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-13-14765

We investigate the plasmonic nanofocusing of terahertz waves in tapered graphene multilayers separated by dielectrics. The nanofocusing effect is significantly enhanced in the graphene multilayer taper compared with that in a single layer graphene taper due to interlayer coupling between surface plasmon polaritons. The results are optimized by choosing an appropriate layer number of graphene and the field amplitude has been enhanced by 620 folds at λ = 50 μm. Additionally, the structure can slow light to a group velocity ~1/2815 of the light speed in vacuum. Our study provides a unique approach to compress terahertz waves into deep subwavelength scale and may find great applications in terahertz nanodevices for imaging, detecting and spectroscopy.

© 2016 Optical Society of America

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