A Low-Nonlinearity Laser Heterodyne Interferometer with Quadrupled Resolution in the Displacement Measurement

Quantitative analysis has been applied extensively for modeling and compensation of periodic non-linearities since the invention of heterodyne laser interferometers. In this article, we mathematically analyze and modele the nonlinearity resulting from non-orthogonality and ellipticity of the polarized laser beams for a modified high-resolution nano-displacement measuring system based on a three-mode laser interferometer. Also, we present a simple method to compensate for the periodic nonlinearity in the modified system based on a two-mode type nonlinearity reduction method. The results reveal that the factor of nonlinearity reduction can reach a value of 99.9% for some special cases of deviations resulting from non-ideal polarized light. In addition to the nonlinearity compensation, we show that the resolution of the displacement measurement in the modified system is doubled and quadrupled with respect to the conventional three-and two-mode laser heterodyne interferometers, respectively.