Length Measurement of Gauge Blocks Using a 3.39 µm He-Ne Laser Interferometer

An infrared interferometer is described for length measurement which uses a simply stabilized 3.39 µm He-Ne laser as a light source and has a piezoelectric-transducer scanning system for recording interference fringes of two fields of view simultaneously and automatically. Pointing accuracy of the order of interference obtained is estimated to be 0.5° in phase. Using this interferometer, the refractive index of air at a wavelength of 3.39 µm is measured with an accuracy of 3 × 10 -8 and Edlén's dispersion formula is confirmed with an accuracy of less than one part in 10 7 . The length of a gauge block of nominal length 200 mm is measured with an accuracy of 5 × 10 -8 in standard deviation.