Infrared He–Xe laser interferometry for measuring length

A technique is described for determining absolute lengths up to 3 m from measurement of the interference fringe fractions for multiple wavelengths. The required accuracies of the wavelength ratio and fringe fraction reading are analyzed. To satisfy the accuracies, a low-cost simply stabilized He-Xe laser, operating simultaneously at two wavelengths, 3.51 and 3.37 microm, was developed. Using this laser the preliminary measurement of the wavelength ratio was made interferometrically with the length standard of a gauge block.