Abstract
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.
Highlights
Over the past decades, terahertz (THz) radiation becomes one of the most intensive research fields in modern science and technology because of its unique characteristics and wide potential applications[1,2,3,4]
It is known that surface plasmon polaritions (SPPs) in planar graphene always lie below the light line in dielectrics and cannot be transformed into radiation
In what follows we shall show that SPPs modes can cross the light line of the dielectrics and transformation of SPPs into radiation becomes possible
Summary
Tao Zhao[1,2], Sen Gong[1,2], Min Hu1,2, Renbin Zhong[1,2], Diwei Liu[1,2], Xiaoxing Chen[1,2], Ping Zhang[1,2], Xinran Wang[2,3], Chao Zhang[2,4], Peiheng Wu2,3 & Shenggang Liu[1,2]. 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. We shall demonstrate that the circular cylindrical graphene structure is an excellent candidate for THz sources which are coherent, with high power density and great tunability. The mechanism involves two processes, (i) excitation of SPPs in circular cylindrical graphene structures with a CEB inside the light cone of the dielectrics, and (ii) immediate transformation of the excited SPPs into Cherenkov THz radiation. This synchronization assures that SPPs can gain energy from the electron beam continuously to compensate the loss due to the radiation and decay Both monolayer and double-layer graphene structures are proposed and studied. In case of the double-layer structure, two-color THz radiation can be achieved
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