Abstract-High power Continuously Frequency-tunable Terahertz Radiation Sources and Transmission Lines for DNP-enhanced NMR System

Diwei Liu, Tao Song,  Hao Shen,  Jie Huang, Ning Zhang, Chenghai Wang, Wei Wang, Shenggang Liu

https://ieeexplore.ieee.org/document/8510299

The effect of the electron beam quality of a 250GHz continuously frequency-tunable gyrotron used for Dynamic Nuclear Polarization enhanced Nuclear Magnetic Resonance is tuned by changing the operating voltage Vo or the operating magnetic field Bo on the operating frequency and the beam-wave interaction efficiency is investigated. Meanwhile, an improved transmission and mirror system with a well-focused Gaussian-like output beam is designed to match the DNP-NMR sample.

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.