Abstract-Enhancement of Spintronic Terahertz Emission via Annealing in Ferromagnetic Heterostructures

Xiaojun Wu, Yang Gao, Yanbin He, Tianxiao Nie, Chun Wang, Deyin Kong, Chandan Pandey, Bo Wang, Lianggong Wen, Weisheng Zhao, Cunjun Ruan, Jungang Miao, Li Wang, Yutong Li, Kang L. Wang

https://arxiv.org/abs/1812.07113

We systematically investigate the influence of annealing effect on terahertz (THz) generation from CoFeB based magnetic nanofilms driven by femtosecond laser pulses. Three times enhancement of THz yields are achieved in W/CoFeB through annealing effect, and double boosting is obtained in Pt/CoFeB. The mechanism of annealing effect originates from the increase of hot electron mean free path induced by crystallization, which is experimentally corroborated by THz transmission measurement on time-domain spectroscopy. Comparison studies of the thickness dependent THz efficiency after annealing are also implemented, and we eventually conclude that annealing and thickness optimization are of importance for scaling up THz intensity. Our observations not only deepen understanding of the spintronic THz radiation mechanism but also provide normal platform for high speed spintronic opto-electronic devices.

Abstract-Broadband Magnetic-Manipulated Spintronic Terahertz Emitter with Arbitrarily Tunable Polarizations

Xiaojun Wu, Deyin Kong, Tianxiao Nie, Bo Wang, Meng Xiao, Chandan Pandey, Yang Gao, Lianggong Wen, Weisheng Zhao, Cunjun Ruan, Jungang Miao, Li Wang, Yutong Li

https://arxiv.org/abs/1809.10474

Flexible manipulation of terahertz-wave polarization during the generation process is very important for terahertz applications, especially for the next-generation on-chip functional terahertz sources. However, current terahertz emitters could not satisfy such demand, hence calling for new mechanism and conceptually new terahertz source. Here we demonstrate a magnetic-field-controlled, highly-efficient, cost-effective, and broadband terahertz source with flexible switch of terahertz polarization states in ferromagnetic heterostructures driven by femtosecond laser pulses. We verify that the chirality, azimuthal angle, and ellipticity of the generated elliptical terahertz waves can be independently manipulated by delicately engineering of the external applied magnetic fields via effectively manipulating the photo-induced spin currents. Such an ultrafast photomagnetic interaction-based, magnetic-field-controlled, and broadband tunable solid-state terahertz source integrated with terahertz polarization tunability function not only has the capability to reveal physical mechanisms of femtosecond spin dynamics, but also demonstrates the feasibility to realize novel on-chip terahertz functional devices, boosting the potential applications for controlling elementary molecular rotations, phonon vibrations, spin precessions, high-speed terahertz communication, and accelerating the development of ultrafast terahertz opto-spintronics.

Abstract-The Fabrication of Large-Area, Uniform Graphene Nanomeshes for High-Speed, Room-Temperature Direct Terahertz Detection

Weiqing Yuan, Min Li, Zhongquan Wen, Yanling Sun, Desheng Ruan, Zhihai Zhang, Gang Chen, Yang Gao, 

• https://link.springer.com/article/10.1186/s11671-018-2602-6

In recent years, graphene nanomesh (GNM), a material with high flexibility and tunable electronic properties, has attracted considerable attention from researchers due to its wide applications in the fields of nanoscience and nanotechnology. Herein, we have processed large-area, uniform arrays of rectangular graphene nanomesh (r-GNM) and circular graphene nanomesh (c-GNM) with different neck widths by electron beam lithography (EBL). The electronic properties of those high-quality GNM samples have been characterized systematically. Electrical measurements illustrated that top-gated field effect transistors with different neck widths of the GNM possessed different Ion/Ioff ratios. In particular, the devices based on r-GNM with a neck width of 30 nm were found to possess the largest Ion/Ioff ratio of ~ 100, and the band gap of the r-GNM was estimated to be 0.23 eV, which, to the best of authors’ knowledge, is the highest value for graphene ribbons or a GNM with a neck width under 30 nm. Furthermore, the terahertz response of large-area r-GNM devices based on the photoconductive effect was estimated to be 10 mA/W at room temperature. We also explored the practical application of terahertz imaging, showing that the devices can be used in a feasible setting with a response time < 20 ms; this enables accurate and fast imaging of macroscopic samples.

Abstract-High resolution continuous wave terahertz spectroscopy on solid-state samples with coherent detection

De-Yin Kong, Xiao-Jun Wu, Bo Wang, Yang Gao, Jun Dai, Li Wang, Cun-Jun Ruan, and Jun-Gang Miao

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-14-17964

We systematically investigate the data analysis methods in terahertz frequency domain spectroscopy (THz-FDS) with coherent detection. We demonstrate that the Hilbert transform method is one of the most appropriate for data processing in THz-FDS. By converting frequency-domain signal into time domain with further data processing, the system noise due to Fabry–Pérot (FP) interference is greatly restrained. Accurate permittivity of lactose monohydrate is successfully extracted under the condition of the existence of atmospheric water vapor. Our work greatly promotes the development of THz spectroscopy in practical applications.

© 2018 Optical Society of America

Abstract-Investigation of mechanism: spoof SPPs on periodically textured metal surface with pyramidal grooves

• Lili Tian
• , Jianlong Liu
• , Keya Zhou
• , Yang Gao
•  & Shutian Liu

https://www.blogger.com/blogger.g?blogID=124073320791841682#editor/target=post;postID=4769349778953500837

In microwave and terahertz frequency band, a textured metal surface can support spoof surface plasmon polaritons (SSPPs). In this paper, we explore a SSPPs waveguide composed of a metal block with pyramidal grooves. Under the deep subwavelength condition, theoretical formulas for calculation of dispersion relations are derived based on the modal expansion method (MEM). Using the obtained formulas, a general analysis is given about the properties of the SSPPs in the waveguides with upright and downward pyramidal grooves. It is demonstrated that the SSPPs waveguides with upright pyramidal grooves give better field-confinement. Numerical simulations are used to check the theoretical analysis and show good agreement with the analytical results. In addition, the group velocity of the SSPPs propagating along the waveguide is explored and two structures are designed to show how to trap the SSPPs on the metal surface. The calculation methodology provided in this paper can also be used to deal with the SSPPs waveguides with irregular grooves.