Air refractometer

摘要

An optical measuring light path formed by a vacuum-side laser beam (Pa) as a reference standard and an optical measuring light path formed by a gas-side laser beam (Pb) as a dimension to be measured are coaxially located sandwiching a movable end (optical transparent body 12) of a vacuum container (11) in order to satisfy Abbe's principle requiring linear disposition of the reference standard and the dimension to be measured in measurement direction, thereby reducing measurement error in measuring air refractive index and improving measurement accuracy therefor.