Abstract-Optical bistability induced by nonlinear surface plasmon polaritons in graphene in terahertz regime

Matthew Sanderson¹, Yee Sin Ang¹, Sen Gong^2,3, Tao Zhao^2,3, Min Hu^2,3, Renbin Zhong^2,3, Xiaoxing Chen^2,3, Ping Zhang^2,3, Chao Zhang^1,3,a) and Shenggang Liu^2,3
http://scitation.aip.org/content/aip/journal/apl/107/20/10.1063/1.4936232?TRACK=RSS
a) czhang@uow.edu.au
Appl. Phys. Lett. 107, 203113 (2015); http://dx.doi.org/10.1063/1.4936232

We demonstrate optical bistability in a prism-air-graphene-dielectric structure. Under a moderate electric field in the terahertz frequency regime, the third order nonlinear optical conductivity is comparable to the linear conductivity. The nonlinear conductivity enhances the energy of surface plasmonpolaritons. Both the energy and frequency of the surface plasmonpolaritons depend on the strength of the nonlinear current in the graphene layer. When considering excitation in the Kretschmann configuration, the reflectance as a function of frequency exhibits bistability. The origin of the bistability is the field dependence of the plasmon mode. We have determined the parameter regime for the occurrence of bistability in this structure.

Abstract-Coherent and Tunable Terahertz Radiation from Graphene Surface Plasmon Polarititions Excited by Cyclotron Electron Beam

Tao Zhao

, Sen Gong

, Min Hu

, Renbin Zhong

, Diwei Liu

, Xiaoxing Chen

, Ping Zhang

, Xinran Wang

,Chao Zhang

, Peiheng Wu

 & Shenggang Liu

http://www.nature.com/articles/srep16059

Terahertz (THz) radiation can revolutionize modern science and technology. To this date, it remains big challenges to develop intense, coherent and tunable THz radiation sources that can cover the whole THz frequency region either by means of only electronics (both vacuum electronics and semiconductor electronics) or of only photonics (lasers, for example, quantum cascade laser). Here we present a mechanism which can overcome these difficulties in THz radiation generation. Due to the natural periodicity of 2π of both the circular cylindrical graphene structure and cyclotron electron beam (CEB), the surface plasmon polaritions (SPPs) dispersion can cross the light line of dielectric, making transformation of SPPs into radiation immediately possible. The dual natural periodicity also brings significant excellences to the excitation and the transformation. The fundamental and hybrid SPPs modes can be excited and transformed into radiation. The excited SPPs propagate along the cyclotron trajectory together with the beam and gain energy from the beam continuously. The radiation density is enhanced over 300 times, up to 105 W/cm2. The radiation frequency can be widely tuned by adjusting the beam energy or chemical potential. This mechanism opens a way for developing desired THz radiation sources to cover the whole THz frequency regime.

Coherent and tunable terahertz radiation from graphene surface plasmon polaritons excited by an electron beam

Shenggang Liu^1,2,a), Chao Zhang^1,2,3, Min Hu^1,2, Xiaoxing Chen^1,2, Ping Zhang^1,2, Sen Gong^1,2, Tao Zhao^1,2 and Renbin Zhong^1,2
 HIDE AFFILIATIONS
1 Terahertz Research Centre, School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu, Sichuan 610054, China
2 Cooperative Innovation Centre of Terahertz Science, Chengdu, Sichuan 610054, China
3 School of Physics and Institute for Superconducting and Electronic Materials, University of Wollongong, New South Wales 2522, Australia
a) liusg@uestc.edu.cn
Appl. Phys. Lett. 104, 201104 (2014); http://dx.doi.org/10.1063/1.4879017
http://scitation.aip.org/content/aip/journal/apl/104/20/10.1063/1.4879017

Although surface plasmon polaritons (SPPs) resonance in graphene can be tuned in the terahertz regime, transforming such SPPs into coherent terahertz radiation has not been achieved. Here, we propose a graphene-based coherent terahertz radiation source with greatly enhanced intensity. The radiation works at room temperature, it is tunable and can cover the whole terahertz regime. The radiation intensity generated with this method is 400 times stronger than that from SPPs at a conventional dielectric or semiconducting surface and is comparable to that from the most advanced photonics source such as a quantum cascade laser. The physical mechanism for this strong radiation is presented. The phase diagrams defining the parameters range for the occurrence of radiation is also shown.