Three-degrees-of-freedom laser interferometer based on differential wavefront sensing with wide angular measurement range.

We present a three-degrees-of-freedom laser interferometer based on differential wavefront sensing with a wide angular measurement range. To obtain measurement signals with a high AC/DC ratio and improve the linearity of differential wavefront sensing in a wide range angular displacement measurement, a fiber bundle instead of a quadrant photodiode is applied to receive the interference light. Meanwhile, a decoupled algorithm with quadratic correction derived by the ray tracing method and kinematic analysis is detailed in the case of the wide range angular displacement. The simulation and experimental results prove that the laser interferometer with the proposed structure could realize hundreds of microradian range of angular displacement measurement, which are expanded in the differential wavefront sensing.