Laser feedback interferometry based on high density cosine-like intensity fringes with phase quasi-quadrature

A novel laser feedback interferometry based on high-order feedback is presented and realized for the first time. The interferometer uses a birefringence dual frequency laser and a tilted feedback mirror with high amplitude reflectivity to generate high density cosine-like optical fringes. These optical fringes have nanoscale resolution. Particularly, phase quasi-quadrature between the dual frequency fringes is obtained because of the phase shift caused by the changes of external optical path length. This phase characteristic can be used to distinguish the direction of movement easily. Under typical room conditions, the system's resolution is 0.51nm in 850μm range, and its 2 min displacement accuracy is 5nm.