Abstract-Circular-Photon-Drag-Effect-Induced Elliptically Polarized Terahertz Emission from Vertically Grown Graphene

Lipeng Zhu, Zehan Yao, Yuanyuan Huang, Chuan He, Baogang Quan, Junjie Li, Changzhi Gu, Xinlong Xu, and Zhaoyu Ren

https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.12.044063

Circular photon drag effect (CPDE) is important for helicity-dependent optoelectronic emitters and detectors yet is less studied in graphene due to the relatively weak light-matter interaction and is submerged by other nonlinear optical effects. We give experimental evidence of CPDE in vertically grown graphene (VGG) by terahertz (THz) emission spectroscopy. The emitted THz polarization states can be tuned to linear, left-handed, and right-handed elliptical polarizations by changing the helicity of the pump laser. Polarity reversal of the THz time-domain signal occurs with the opposite helicity of pump laser excitation due to the CPDE. Theory analysis suggests that both the linear photon drag effect and CPDE-induced transient photocurrents contribute to the THz emission from which the contribution weight of CPDE can be tuned by different elliptical states of the excitation light. The photon-helicity-dependent THz emission from VGG based on CPDE offers an alternative thought of graphene-based polarization sensitive THz sources for chiral analysis in the THz field.

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Abstract-Towards Ultra-strong Terahertz Field Enhancement in Nanogap Split Ring Resonators

Jiahui Cao, Baogang Quan, Kanglong Chen, Bo Wang, Li Wang, and Xiaojun Wu

https://www.osapublishing.org/abstract.cfm?uri=ISUPTW-2018-WI12

We design and fabricate terahertz split ring resonators with nanogaps for extremely high field enhancement factor of >100000 when the splitting gap is sub-10 nm, and the experimental results agree very with the simulated results.

© 2018 OSA

Abstract-Enhanced Polarization-sensitive Terahertz Emission from Vertical Grown Graphene by Dynamical Photon drag Effect

Lipeng Zhu,  Yuanyuan Huang,  Zehan Yao,  Baogang Quan,  Longhui Zhang ,  Junjie Li,  changzhi gu,  Xin Long Xu  and  Zhaoyu Ren 

http://pubs.rsc.org/en/content/articlelanding/2017/nr/c7nr02227a#!divAbstract

Improving terahertz (THz) emission from graphene is a challenge for graphene-based THz photonics as graphene demonstrates a weak light-matter interaction. With an unique ultra-black surface structure, vertical grown graphene (VGG) is proposed to enhance the light-matter interaction and further enhance THz emission. Herein, enhanced THz radiation is observed by THz time-domain emission spectroscopy from VGG compared with single-layer graphene. The radiated THz amplitude shows a linear dependence on the pump power, which demonstrates a second order nonlinear effect. Considering the symmetry of VGG on substrate, we can exclude the optical rectification effect and photogalvanic effect (PGE) by the D6h point group with centrosymmetry. Thus we analyze the transient photocurrent related to THz emission only by the photon drag effect (PDE). The polarization-sensitive THz radiation signals are wave-vector reliance and demonstrate cos2φ and sin2φ dependence on the polarization angles of the pump laser. This is consistent with the theoretical analysis of PDE. Our results show the enhanced, ultrafast, broadband THz radiation property of VGG, which paves the way for high performance of THz emitter and THz detector based on graphene materials.

Abstract-Optical modulation of terahertz behavior in silicon with structured surfaces

Xiaojun Wu, Xuecong Pan, Baogang Quan, and Li Wang

http://apl.aip.org/resource/1/applab/v103/i12/p121112_s1?isAuthorized=no

Optically modulated terahertz (THz) transmittance through Si with various resistivities, in particular the high-resistivity samples with a structured surface showing nanosized pillars or split-ring resonators (SRRs), was investigated. The samples with nanosized pillars display an increased transmittance and an accordingly reduced modulation depth. With SRRs on the surface, strongly selective modulation can be realized at the resonant frequencies where the transmittance is vanishingly small, whereas at the non-resonant frequencies, where the transmittance is large, the modulation depth is much greater. These results demonstrate an alternative route for the modulation of THz wave in the all-optical devices.

© 2013 AIP Publishing LLC

Article & Abstract-Design of a polarization insensitive multiband terahertz metamaterial absorber

Fangrong Hu, Li Wang, Baogang Quan, Xinlong Xu, Zhi Li, Zhongan Wu,  Xuecong Pan
My Note: you can read the entire article here:
http://m.iopscience.iop.org/0022-3727/46/19/195103/

We design a terahertz (THz) metamaterial absorber having four narrowband high absorptivities of 98%, 97%, 98% and 97% at frequencies of 0.68 THz, 1.27 THz, 2.21 THz and 3.05 THz, respectively. The absorber consists of three metallic layers, which are separated by two dielectric spacers. The absorption performances are simulated using a commercialized full-wave electromagnetic simulation software, and the mechanism of absorption is theoretically investigated. The result shows that the absorber is insensitive to the polarization of THz wave and the position of every absorption peak can be effectively tuned by the geometries of the absorber. The potential applications of the absorber include spectrally selective detecting, THz sensing and thermal imaging.

Abstract-Self-referenced sensing based on terahertz metamaterial for aqueous solutions

http://apl.aip.org/resource/1/applab/v102/i15/p151109_s1?isAuthorized=no

Xiaojun Wu¹, Xuecong Pan¹, Baogang Quan¹, Xinlong Xu^1,2, Changzhi Gu¹, and Li Wang¹

¹Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
²Nanobiophotonic Center, State Key Laboratory for Incubation Base of Photoelectric Technology and Functional Materials, Institute of Photonics & Photon-Technology, Northwest University, Xi'an 710069, China 

We demonstrated a self-referenced sensing method in reflection geometry for characterizing aqueous solutions based on terahertz metamaterials. The sensing signal and the reference signal are taken in one measurement from different interfaces of the substrate. For ethanol-water mixture and aqueous solution of NaCl, the line-shape of the modulated response shows distinct polarity, while the peak-valley value near resonant region depends linearly on the solution concentration. These observations result from the variation of dielectric environment near the interface between the metamaterials and the aqueous solutions. This method holds promise for future application in monitoring real aqueous biosystems and ecological water systems.