Abstract-Achromatic terahertz Airy beam generation with dielectric metasurfaces

 

Qingqing Cheng , Juncheng Wang, Ling Ma, Zhixiong Shen, Jing Zhang, Xiaoying Zheng ,Tao Chen, Ye Yu, Dong Yu, Qiong He, Wei Hu, Tao Li, Songlin Zhuang,  Lei Zhou

https://www.degruyter.com/view/journals/nanoph/ahead-of-print/article-10.1515-nanoph-2020-0536/article-10.1515-nanoph-2020-0536.xml?rskey=WV2s5h&result=7&tab_body=abstract

Airy beams exhibit intriguing properties such as nonspreading, self-bending, and self-healing and have attracted considerable recent interest because of their many potential applications in photonics, such as to beam focusing, light-sheet microscopy, and biomedical imaging. However, previous approaches to generate Airy beams using photonic structures have suffered from severe chromatic problems arising from strong frequency dispersion of the scatterers. Here, we design and fabricate a metasurface composed of silicon posts for the frequency range 0.4–0.8 THz in transmission mode, and we experimentally demonstrate achromatic Airy beams exhibiting autofocusing properties. We further show numerically that a generated achromatic Airy-beam-based metalens exhibits self-healing properties that are immune to scattering by particles and that it also possesses a larger depth of focus than a traditional metalens. Our results pave the way to the realization of flat photonic devices for applications to noninvasive biomedical imaging and light-sheet microscopy, and we provide a numerical demonstration of a device protocol.

Abstract-Broadband achromatic metalens in terahertz regime

Qingqing Cheng, Meilin Ma, Dong Yu, Zhixiong Shen, Jingya Xie, Juncheng Wang, Nianxi Xu, Hanming Guo, Wei Hu, Shuming Wang, Tao Li, Songlin Zhuang



https://www.sciencedirect.com/science/article/pii/S2095927319304621

Achromatic focusing is essential for broadband operation, which has recently been realized from visible to infrared wavelengths using a metasurface. Similarly, multi-terahertz functional devices can be encoded in a desired metasurface phase profile. However, metalenses suffer from larger chromatic aberrations because of the intrinsic dispersion of each unit element. Here, we propose an achromatic metalens with C-shaped unit elements working from 0.3 to 0.8 THz with a bandwidth of approximately 91% over the centre frequency. The designed metalens possesses a high working efficiency of more than 68% at the peak and a relatively high numerical aperture of 0.385. We further demonstrate the robustness of our C-shaped metalens, considering lateral shape deformations and deviations in the etching depth. Our metalens design opens an avenue for future applications of terahertz meta-devices in spectroscopy, time-of-flight tomography and hyperspectral imaging systems.

Abstract-Study of protein conformation change induced by pH condition using terahertz spectroscopy

Jun Zhou, Xin Rao, Junhong Tian,  Jiafu Wang, Tao Li,

https://ieeexplore.ieee.org/document/8068501/

The terahertz absorption spectra of BSA (Bovine Serum Albumin) in aqueous solution were measured under different pH values from 2.2 to 8. The absorption spectra were analyzed using the two-dimensional correlation spectroscopy (2DCOS). By comparing the cross peaks corresponding to the different pH values, it can be obtained that the conformation is related to the pH condition.

Abstract-Tunable unidirectional surface plasmon polariton launcher utilizing a graphene-based single asymmetric nanoantenna

Lei Huang, Shan Wu, Yulin Wang, Xiangjun Ma, Hongmei Deng, Shuming Wang, Ye Lu, Chuanqi Li, and Tao Li

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-7-2-569&origin=search

We design and numerically investigate a graphene-based asymmetric nanoantenna microstructure that can be used to realize electrically controllable, unidirectionally propagating broadband surface plasmon polaritons. The device geometry facilitates the simultaneous excitation of two localized surface plasmons resonances in the whole structure, and consequently, the asymmetric nanoantenna can be considered as being composed of two oscillating magnetic dipoles, wherein the interference of the radiated electromagnetic waves leads to a unidirectional propagation effect. Our results indicate that our proposed active device is promising for realizing compactable, tunable, terahertz plasmonic light sources.

© 2017 Optical Society of America

Abstract-High speed optical modulation of terahertz waves using annealed silicon wafer

Tao Li   Dongxiao Yang   Jian Wang 
http://www.opticsjournal.net/abstract.htm?id=OJ140723000031C0FbIe

Modulation properties of terahertz waves going through a light excited high resistivity silicon wafer are analyzed and measured. Free carrier lifetime of the silicon wafer affects the modulation depth and speed of the terahertz wave. The lifetime is reduced to less than 1 μs by thermal processing for high speed modulation. Experimental results show that the response time and modulation depth of the proposed modulating structure are close to 1 μs and 51%, respectively.

Abstract-Role of surface plasmon resonant modes in anomalous terahertz transmission through double-layer metal loop arrays

Song Xia, Dongxiao Yang, Tao Li, Xiang Liu, and Jian Wang  »View Author Affiliations

Optics Letters, Vol. 39, Issue 5, pp. 1270-1273 (2014)
http://dx.doi.org/10.1364/OL.39.001270

A three-layer construction was proposed to induce anomalous transmission response for a normal incidence of terahertz (THz) wave. This structure was composed of a dielectric layer of quartz and two metallic layers, which were deposited on the two surfaces of quartz and patterned the same periodic arrays of subwavelength air circular loop. Based on comparative analyses of dispersion relations of both the structure and its partial structures, propagating surface plasmon and localized surface plasmon principally dominated the lower and higher resonant peaks appearing in the calculated transmittance spectrum, respectively. A sample was fabricated by laser technology for experiment and the measured THz transmission showed a good agreement with simulation, providing reference for potential applications.

© 2014 Optical Society of America