High-precision 12-times optical subdivision heterodyne laser interferometer for short-distance measurement

Heterodyne laser interferometers are based on high-directional and high-coherence laser wavelengths, have broad application prospects in the fields of nano-scale multi-axis joint control of ultra-precision five-axis machine tools and sub-nano alignment positioning of high-end lithography machines. It is necessary to improve the measurement accuracy of the measurement mirror group to enhance its theoretical resolution limit. However, traditional heterodyne methods are limited by optical subdivision accuracy and spatial positioning accuracy. To meet this challenge, we propose a high-precision 12-times optical subdivision heterodyne laser interferometer for short-distance measurement, which not only avoids the problems of measurement accuracy reduction due to insufficient optical subdivision multiples and the difficulty of adjustment due to the increase in the number of reflections, but also reduces the influence of periodic nonlinear errors. By introducing space position and equal optical path, it makes better use of the Doppler frequency shift information superposition characteristic of short distance interferometry, compared with the traditional 4-times optical subdivision mirror group. It further proves the advantages of the proposed 12-times optical subdivision mirror group in short distance high-precision measurement, and its theoretical resolution is better than 0.103 nm. Experiments prove that the actual test results show the dynamic resolution is better than 1 nm, the dynamic error in vertical movement state is better than ±10nm@20 mm, the dynamic error in horizontal movement state is better than 35 nm@20 mm, and the stable step measurement error is better than ±1 nm. Therefore, the proposed method is effective for ultra-precise positioning and ultra-precise displacement measurement.