Terahertz emission from unbiased YBa₂Cu₃O₇ films

The observed terahertz emission from unbiased YBa₂Cu₃O₇ at room temperature excited by 1.5-eV and 3-eV 150-fs laser pulses are described. Terahertz waveforms measured from samples of YBCO and InP at an incident angle of θ = 50°, for different incident and emitted polarizations, are compared. The peak-to-peak amplitude of the terahertz radiation emitted from the YBCO was found to increase linearly as the incident power is varied from 10 to 100 mW at 800 nm. For 400 nm excitation, the emitted terahertz radiation also increased linearly with excitation fluence. No terahertz emission was observed from an insulating sample of YBCO (YBa₂Cu₃O_6.2) grown on MgO which was optically excited under the same experimental conditions as the doped sample.