THZ EMISSION FROM HIGH-T-C SUPERCONDUCTORS BY OPTICAL PULSE EXCITATION

Emission of ultrashort electromagnetic pulses from current-biased supe rconducting YBCO films has been observed by exciting with femtosecond laser pulses. The emission device is made of YBCO strip lines with a b ridge at their center on an MgO substrate. The electric field of the p ulse is detected by a photoconductive switch made of LT-GaAs, The emit ted pulse width is similar to 0.5 psec and its Fourier component exten ds up to 2 THz. Characteristics of the THz emission such as bias curre nt, pump power and temperature dependence are Investigated in detail. The emission mechanism is ascribed to the ultrafast supercurrent modul ation caused by the photoexcitation.