Note: A small roll angle measurement method with enhanced resolution based on a heterodyne interferometer.

Small roll angle is hard to be measured directly by commercial interferometer instruments due to their low sensitivities in axial direction. A method for its measurement based on a heterodyne interferometer is presented, which adopts accessories including a half wave plate, a multiple-reflector, and a phase meter to achieve test by detecting phase differences between the measurement and reference arms. Mathematical model reveals the resolution will be improved by increasing pass times through the half wave plate. The theoretical resolution is up to 0.19 in. when the pass times increase to three and the phase meter resolution is 0.01°. The proposed method is proved by the experiment.