| 摘要 |
Apparatus capable of measuring either changes in the refractive index, or, if desired, the absolute refractive index, of a gas is provided which comprises a differential plane mirror interferometer to produce a pair of measurement beams and a pair of reference beams; and a gas-tight refractive index cell means (78) comprised, most preferably, of a window (70) affixed to the end of a cylindrical tube (73) closest to the interferometer and a mirror (75) affixed to the other end of the tube (73), the cell (78) being aligned to the interferometer so that the reference beams pass inside of the tube (73) in a sealed volume and the measurement beams pass outside of the tube (73), such as in ambient air, for the measurement of changes in the refractive index of the gas surrounding the gas-tight cell (78). When the absolute refractive index of a gas is to be measured, the gas-tight cell (78) comprises, most preferably, a window (70) affixed to the ends of a pair of cylindrical concentric tubes (73, 86) closest to the interferometer and a mirror (75) affixed to the other ends of the tubes (73, 86) to provide two sealed volumes, with the cell (78) being aligned to the interferometer so that thereference beams pass through the sealed volume of the inner tube (73) of the pair (73, 86) which is evacuated, and the measurement beams pass through the sealed volume between the tubes (73, 86), which sealed volume is either evacuated or contains the gas whose absolute refractive index is to be measured. In both embodiments, means (90, 92) for measuring the phae variation between the reference and measurement beams after they traverse the gas-tight cell (78); and means, most preferably a microcomputer, for converting the measured phase variation to provide an output which is either the changes in or the absolute refractive index of a gas are provided.
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