Microwave Current Imaging in Passive HTS Components by Low-Temperature Laser Scanning Microscopy (LTLSM)

We have used the Low-Temperature Laser Scanning Microscope (LTLSM) technique for a spatially resolved investigation of the microwave transport properties, nonlinearities, and material inhomogeneities in an operating coplanar waveguide YBa₂Cu₃O$_{7‐δ}$ (YBCO) microwave resonator on a LaAlO₃ (LAO) substrate. The influence of twin-domain blocks, in-plane rotated grains, and micro-cracks in the YBCO film on the nonuniform radiofre-quency (rf) current distribution was measured with a micrometer-scale spatial resolution. The impact of the peaked edge currents and rf field penetration into weak links on the linear device performance were also studied. The LTLSM capabilities and its future potential for nondestructive characterization of the microwave properties of superconducting circuits are discussed.