High Temperature Superconductor Terahertz Emitters: Fundamental Physics and Its Applications

Coherent and continuous radiation sources of the electromagnetic (EM) waves at terahertz (1 THz = 10 12 c/s) frequencies using a mesa structure fabricated from high temperature superconducting Bi 2 Sr 2 CaCu 2 O 8+δ single crystals are described with a special emphasis on the physics of the radiation mechanism and the applications. After the intensive studies of many mesas fabricated with different conditions, it is revealed that the ac-Josephson effect works as a primary driving mechanism of the radiation and the cavity resonance needed for stronger radiation plays an additional role to the mechanism, although both are working together while radiating. A prototype of the imaging machine for multipurpose uses has successfully been developed.