Emission of continuous terahertz waves by high Tc superconductors

Continuous coherent terahertz waves have various kinds of application such as biology and information science. One of the hurdles for technical advancements in the terahertz region of electromagnetic wave is development of sources for intense and continuous coherent and frequency tunable terahertz waves. Therefore, we investigate a mechanism for emitting the terahertz waves by using high Tc superconductors. High Tc superconductors form naturally stacked Josephson junctions. In the junctions there appears an excitation called Josephson plasma, the frequency of which is in the range of terahertz. The frequency appears inside the superconducting main energy gap and the Landau damping is weak. Therefore, if the Josephson plasma is excited in someway, the excited plasma decays by emitting an electromagnetic wave. When an external current and a magnetic field are applied to the sample, fluxon flow induces a voltage. The voltage creates oscillation current through the Josephson effect, and the current excites the Josephson plasma waves with terahertz frequencies. In the present work we perform simulation of terahertz emission using Earth Simulator. We used the parameters corresponding to Bi2Sr2CaCu2O8+δ and obtained the following results. The sample itself works as a cavity, and the input energy given by an external current is stored in a form of standing wave of the Josephson plasma. A part of the energy is emitted as terahertz waves. The emitting electromagnetic wave is continuous coherent terahertz waves with the power of an order of 1000 W/cm2. The frequency is tunable by changing the applied current.