Thermal and Optical Tuning of Resonant Frequency in YBCO Thin Films

초록

The modulation of the resonant freuency is used to determine the optical response of YBCO thin films under both thermal and optical perturbations. The frequency domain measurements are performed by monitoring the change of microwave resonance mode frequency and frequency width in a temperature range of 20 K to 80 K. The optical excitation consisted of a 70 psec laser pulse train at 532nm, generted by an actively mode-locked Nd:YAG laser. The pair-breaking effects induced by two external perturbations show the quadratic dependence of the perturbation in the range of 0.26Xc to 0.56Xc and the perturbation to the fourth dependence above 0.63Xc, where Xc is either the critical temperature or the critical optical pulse energy at which the resonance can no longer be distinguished. These results suggest that the optical response of the superconducting thin film is bolometric due to laser heating.