Abstract
We discovered a new type of terahertz (THz) radiation from YBa2Cu3O7-δ thin films. Ultrashort electromagnetic pulses, which are referred to as THz radiation, were emitted into free space by irradiating the superconductive films with femtosecond laser pulses. The THz radiation, with a spectrum extending from 0.1 to 3 THz, was excited in both the films applied with a magnetic field and the flux-trapped films. The results suggest that the screening current for the external magnetic field and circulating current around the trapped flux play an important role in the emission mechanism.