We discovered a new type of terahertz (THz) radiation from YBa2Cu3O7-d
elta (YBCO) thin films. Ultrashort electromagnetic pulses with their s
pectra extending from 0.1 to 3 THz were excited by irradiating magneti
c-flux-trapped YBCO thin films with femtosecond laser pulses. The emis
sion mechanism is discussed in relation to the trapped flux. (C) 1997
Elsevier Science B.V.