High-finesse measurements at low temperatures.

@article{Richard1991HighfinesseMA,
  title={High-finesse measurements at low temperatures.},
  author={Jean-Philippe P. Richard and James J. Hamilton},
  journal={Applied optics},
  year={1991},
  volume={30 25},
  pages={3560-1}
}
High-reflectivity supermirrors were used to produce a Fabry-Perot cavity that operated at cryogenic temperatures. The best finesse below 80 K was found to be 19,000 and remained constant down to 4.2 K.