Emission of continuous coherent terahertz waves with tunable frequency   by intrinsic Josephson junctions
  We present a mechanism for emission of electromagnetic terahertz waves by simulation. High $T_{c}$ superconductors form naturally stacked Josephson junctions. When an external current and a magnetic field are applied to the sample, fluxon flow induces voltage. The voltage creates oscillating current through the Josephson effect and the current excites the Josephson plasma. The sample works as a cavity, and the input energy is stored in a form of standing wave of the Josephson plasma. A part of the energy is emitted as terahertz waves. 
Masashi Tachiki, Mikio Iizuka, Kazuo Minami, Syogo Tejima, and Hisashi   Nakamura