EMISSION PROPERTIES OF YBA2CU3O7-DELTA-FILM PHOTOSWITCHES AS TERAHERTZ RADIATION SOURCES

Terahertz (THz) radiation is generated from biased YBa2Cu3O7-delta (YB CO)-film photoswitches by exciting them with femtosecond (fsec) laser pulses. The pump power, bias current and temperature dependence of the radiation amplitude is measured in order to characterize the emission properties of the high-critical-temperature (high-T-C) superconductin g photoswitches. The radiation amplitude increases superlinearly with increasing pump power in the moderate pump power range and saturates a t high pump power. The bias current dependence of the radiation amplit ude shows superlinear increase for high bias current. The temperature dependence of the radiation amplitude increases with increasing temper ature except near the critical temperature. The features observed in t he measurements are explained by the thermal and transient changes of the complex refractive index, which affects the output coupling effici ency of the THz radiation from the high-T-C superconducting film to th e free space.