the speed of light in undermining method and apparatus for detervarie environmental conditions in combination with an interferometer

摘要

An evacuable tube (30) is used to separate two optical elements (32, 34) spaced at a known predetermined length L. A laser interferometer (20) is arranged to measure the change in apparent distance DELTA between the elements (32, 34) when the tube is filled with ambient air and when the tube is evacuated. An interferometer calibration factor VA can then be determined from the equation VA=1- DELTA /L, where VA is the ratio of the wavelength of light in vacuum to the wavelength of the light in ambient air. This calibration factor VA is used to correct further interferometer measurements for existing ambient environmental conditions of temperature, relative humidity and atmospheric pressure. IMAGE