A Random Angle Error Interference Eliminating Method for Grating Interferometry Measurement Based on Symmetry Littrow Structure

Abstract All linear motion will have random angle errors, which will lead to linear displacement detection result deviating from the true value. To solve this common problem in the field of optical precision measurement, this study proposes a symmetry Littrow grating interferometry measurement method (SLGIM). SLGIM uses high‐precision planar diffraction gratings and place them on both sides of the central main optical system to build two complementary measurement arms with equal optical paths. There is a common mode suppression relationship between the two measurement arms, so the measurement system can eliminate random angle error interference and improve the precision of linear displacement detection. The experiment results show that when the same random angle error interference is applied, compared with the traditional grating measurement system, the mean value of error decreases 25.8%, the standard deviation decreases 37.5%, and the range decreases 33.7%. The result after using the structure proposed achieves nanometer‐level measurement precision.