Low temperature laser scanning microscopy of a superconducting   radio-frequency cavity
  An apparatus was developed to obtain, for the first time, 2D maps of the surface resistance of the inner surface of an operating superconducting radio-frequency niobium cavity by a low-temperature laser scanning microscopy technique. This allows identifying non-uniformities of the surface resistance with a spatial resolution of about one order of magnitude better than with earlier methods and surface resistance resolution of ~ 1 micro-Ohm at 3.3 GHz. A signal-to-noise ratio of about 10 dB was obtained with 240 mW laser power and 1 Hz modulation frequency. The various components of the apparatus, the experimental procedure and results are discussed in detail in this contribution. 
G. Ciovati, Steven M. Anlage, C. Baldwin, G. Cheng, R. Flood, K.   Jordan, P. Kneisel, M. Morrone, G. Nemes, L. Turlington, ...
cond-mat.supr-con physics.acc-ph