Terahertz radiation from high-Tc superconductors excited by femtosecond laser pulses and its application to visualizing supercurrent distribution

The THz radiation by exciting photoconductive antennas or semiconductor surfaces with femtosecond laser pulses opens a new field of ultrashort laser applications. The transient current induced by the laser pulse irradiation is the source of the radiation in these cases. We proposed and demonstrated that the THz radiation is also emitted from high-T_c superconductor (HTSC) thin films under a bias current by exciting with femtosecond laser pulses, and interpreted this phenomenon in terms of the transient supercurrent decrease and recovery associated with the transient Cooper pair breaking. We show the properties of the THz radiation from the HTSCs in some detail and the applications to the visualization of the supercurrent distribution