Simple and compact grating-based heterodyne interferometer with the Littrow configuration for high-accuracy and long-range measurement of two-dimensional displacement.

Abstract

We propose a simple and compact reading head with the Littrow configuration that will increase measurement range and reduce the complexity of a two-dimensional grating-based interferometer. The reading head contains only a beam splitter, two polarizing beam splitter modules, and two mirrors. The theoretical resolutions in two directions are 0.27nm and 0.18nm, respectively. In comparison with a dual-frequency laser interferometer, the proposed interferometer can measure displacement from 3nm to 10mm with high accuracy. The 3σ values in two directions for the difference are 1.67nm and 1.35nm for a displacement of 9nm. Repeatability for a displacement of 1μm is better than 2nm.