Heterodyne angular interferometer using a square prism

An interferometer composed of a dual-frequency laser, sensing assembly, and decoding system is proposed for angular displacement determinations. The laser is a heterodyne light source. The sensing assembly generates an interference signal by the use of a square prism, and the decoding system extracts the phase difference of the interference signal. The theory, which reveals that the phase difference has a relation with the angular displacement of the square prism, of the interferometer is described. A setup constructed to realize the interferometer and the results of using this setup are then demonstrated and presented.