Modulation of the resonance frequency of superconducting microwave resonators

The microwave transmission characteristics of superconducting YBa₂Cu₃O_7-x (YBCO) meander line resonators have been investigated as a function of temperature, optical pulse energy, and input power. The measurements are performed in a temperature range from 20 K 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 optical pulse energy is mapped out from zero to the critical optical pulse energy at which the resonance can no longer be distinguished. The measured resonance frequency shows a squared dependence on both the temperature and the optical pulse energy. As for the dependence on input power, the resonant frequency linearly decreases at a rate of 148 kHz/dBm at 50 K.