Abstract
The results of length measurements made with a 800-mm-long gauge block, using an infrared interferometer whose light source is a 3.51– 3.37-μm simultaneous operation He–Xe laser, are described. The wavelength ratio of the 3.51-μm line to the 3.37-μm line is determined to an accuracy of 1.7×10−8 and the absolute length of the gauge block is uniquely determined to an accuracy of 4.9×10−8 by the method of excess fractions. This interferometer has a possibility of measuring lengths up to several meters.