Development of a double-diffraction grating interferometer for measurements of displacement and angle

A double-diffraction grating interferometer for precision displacement and rotation angle measurement is proposed. The grating interferometer uses electro-optical modulation technology to generate heterodyne light sources, then the "double-diffraction" optical path is established by the cooperation of the mirror and the grating, so that the diffracted light passes through the grating again to generate a diffraction, thereby introducing a doubled phase change to improve the system resolution of the measurement effectively. Then we can obtain the measurement result of the in-plane displacement and the in-plane rotation angle by the measurement result of the light detection. Under this optical path system, the interferometer system can continue to provide correct in-plane displacement and rotation angle measurement information as the grating moves out of plane. The experimental results show that the double-diffraction grating interferometer measurement technology can provide measurement information of double-degree-of-freedom displacement and rotation angle without changing the optical structure. The resolution of the displacement and rotation angle can reach 2 nm and 300 nrad respectively, the repeatability is better than 2 nm and 100 nrad respectively, and the measurement speed limit can reach 160 μm/s, which has excellent measurement performance.