Thermal and optical tuning of the resonant frequency in YBCO thin films

The modulation in the resonant frequency of superconducting passive devices fabricated with YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) thin films has been investigated as a function of temperature and optical pulse energy. The frequency-domain measurements are performed in a closed-cycle refrigerator in a temperature range of 20 to 80 K. The optical excitation consists of a 70 psec laser pulse train at 532 nm from an actively mode-locked Nd:YAG laser. The measured optical pulse energy dependence of the resonant frequency is described by f=f/sub p0/|1-a(P/P/sub c/)/sup 2/| where P/sub c/ is the critical optical pulse energy beyond which resonance has disappeared. As for the dependence on temperature, the resonant frequency can be expressed by f=f/sub T0/|1+2/spl lambda/coth(t//spl lambda/)/d|/sup -1/2/ where the magnetic penetration depth is given by a quadratic dependence on temperature, /spl lambda/=/spl lambda//sub 0/|1-(T/T/sub c/)/sup 2/|/sup -1/2/.