M. Hangyo et al., ULTRAFAST OPTICAL-RESPONSE AND TERAHERTZ RADIATION FROM HIGH-T-C SUPERCONDUCTOR, IEICE transactions on electronics, E80C(10), 1997, pp. 1282-1290
New THz radiation devices made of high-T-c superconductors are fabrica
ted and their characteristics are studied in detail. Ultrashort electr
omagnetic pulses with similar to 0.5 ps width have been radiated into
free space from current biased devices made of superconducting YBa2Cu3
O7 (YBCO) films by exciting with femtosecond laser pulses. The Fourier
spectrum of them extends up to similar to 3 THz. The radiation mechan
ism is ascribed to the ultrafast supercurrent modulation by the optica
l pulses. The THz waveform is analyzed using rate equations describing
the relaxation of photoexcited quasiparticles. By the improvement of
the device structure and the collecting optics, the radiation power ca
n be increased up to similar to 0.5 mu W. A new type THz radiation fro
m YBCO films under an external magnetic field without a tranport curre
nt is also reported.