REFRACTIVE-INDEX MEASURING APPARATUS

PURPOSE:To provide an apparatus for obtaining refractive index readily and highly accurately by using a variable frequency light source, and measuring a vacuum part and an atmospheric part at the same time. CONSTITUTION:The output light from a variable frequency light source 1 is split into two light beams through a beam splitter 2. One light beam is transmitted through the splitter 2, cast into an interferometer 41 and split into two light beams. The light beams are reflected from reflecting surfaces 51a and 51b of an atmospheric part 51 in a reference space part 5, respectively, returned into the interferometer 41 and cast into detector 61. The other light beam is reflected from the beam splitter 2 and a mirror 3, cast into an interferometer 41 and split into two light beams. The light beams are reflected from reflecting surfaces 52a and 52b of a vacuum part 52 in the reference space part 5, respectively, returned into the interferometer 42 and cast into a detector 62. The outputs of the interference signals obtained from the interferometers 41 and 42 are measured in the detectors 61 and 62. The phases are measured with phase measuring devices 71 and 72. The absolute value of the refractive index is obtained in an operator 8 based on the change in phase. Thus, the highly accurate apparatus can be readily obtained.