Detection of light using high temperature superconducting microstrip lines

The authors report the results of measurements of the effects of external light on the transmission of microwaves through superconducting YBa₂Cu₃O_7-δ microstrip lines. The microstrip geometries used include an asymmetric ring and a meander path. Measurements were made as a function of the microwave frequency (up to 12 GHz), temperature (above to below the superconducting transition temperature), and microwave power. The authors variations in the T_c of the superconductor, caused by locally varying microwave current densities (standing-wave component). At low microwave powers, this technique can be used to optically probe the local character of the superconducting film without having to move contacts over the film. The asymmetric ring microstrip interferometer was observed to show light-induced shifts in the null frequencies due to the kinetic inductance effect