Free-space electrooptic sampling of terahertz radiation from optically excited superconducting YBa/sub 2/Cu/sub 3/O/sub 7-(delta)/ thin films

The characteristics of photogenerated terahertz radiation from a current-biased superconducting YBa/sub 2/Cu/sub 3/O/sub 7-(delta)/ (YBCO) bow-tie antenna were investigated using a free-space electrooptic sampling technique. Picosecond electromagnetic pulses about 450 fs wide were obtained. The frequency spectrum derived by Fourier transforming the picosecond pulses spans over 0.1-4 THz. The dynamics of the quasi-particles optically induced by the ultrafast laser pulse primarily determines the performances of the transient terahertz radiation generated under different operating parameters. The results indicate a characteristic quasi-particle relaxation time of about 2.5 ps close to the critical temperature T/sub c/, and a faster time at lower temperatures.