Optical heterodyne grating interferometry for displacement measurement with subnanometric resolution

A novel method for displacement measurement is presented. The measurement system includes a heterodyne light source, a moving grating and a lock-in amplifier for phase measurement. The optical phase variation, which stems from the grating movement, is measured by an optical heterodyne interferometer. The experimental results demonstrate that our system can measure small and long displacement with subnanometric resolution. The theoretical resolution is about 1 pm. By means of isolating the measurement system, the low frequency noise can be reduced, and when only high frequency noises are considered, our method can achieve measurement resolution of about 0.2 nm.