Refractometer for measuring refractive index of air - has measuring path defined by plane parallel rod of defined length

摘要

The refractometer is used in conjunction with a polarisation/optical differential interferometer to allow calibration. Its measuring path is provided by a plane parallel rod of known length with reflective surfaces at its ends. The beam splitter of the interferometer and the rod allow a ranging measurement to be obtained in free air and in a vacuum. A linearly movable measuring mirror (17) allows the refractive index of the air to be measured via a heterodyne path measurement. Pref. the movable measuring mirror (17) is made of the same material as the rod defining the measuring path. USE - For calibration of precision interferometric ranging device.