Resonant terahertz radiation from Tl2Ba2CaCu2O8+δ thin films by ultrafast optical pulse excitation

Abstract

We have observed the free-space radiation of the resonant terahertz wave from c-axis oriented Tl2Ba2CaCu2O8+δ thin films by femtosecond optical pulse excitation under a radial magnetic field of about 100 Oe nearly parallel to the c axis of the thin film. The observed wave form showed clear oscillations up to 80 K. The frequency was shifted from ∼620 GHz at 24 K to ∼300 GHz at 80 K, corresponding to an increase in c-axis penetration depth, λc, from ∼26 μm to ∼53 μm, and disappeared above TC as expected for the Josephson plasma resonance.