Low temperature laser scanning microscopy of a superconducting radio-frequency cavity

TL;DR

This paper introduces a novel low-temperature laser scanning microscopy technique to map the surface resistance of superconducting RF cavities with high spatial resolution, enabling detailed analysis of surface non-uniformities.

Contribution

The authors developed the first apparatus capable of 2D surface resistance mapping of superconducting RF cavities at low temperatures with improved spatial resolution and sensitivity.

Findings

Achieved ~1 micro-Ohm surface resistance resolution at 3.3 GHz.

Obtained 2D maps revealing surface non-uniformities.

Demonstrated high signal-to-noise ratio with modest laser power.

Abstract

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.