When the cryogenic medium is Liquid Oxygen (or Liquid Natural Gas), calibration in water is a better approximation than calibration in air:
Air Refractive Index = 1.000
Liquid Oxygen Refractive index = 1.221
LNG Refractive Index = 1.286
Water Refractive Index = 1.332
A sensor’s operating range is extended in proportion to the ratio of the refractive indices.
For example, to calculate a sensor’s response in LOX, first calibrate the sensor submerged in water. Then remap the displacement data by the ratio 1.221/1.332.