Ultra-low tilt angle measurement using temporal phase shifting in Sagnac interferometer

Temporal phase shifting has been achieved in the Sagnac interferometer for the first time. To achieve this phase shifting, a rectangular parallel glass plate is introduced into one half of the beam, leaving the other half without a parallel glass plate. When rotation is applied to the parallel glass plate, phase shifting occurs. This technique is used to measure the ultra-low tilt angle given to one of the mirrors of the Sagnac interferometer. In this study, we also elaborate on the method to determine the initial angle (rotation angle) of the parallel glass plate with respect to the beam direction. The design of the interferometer, theory for temporal phase shifting, tilt angle measurement, and finding the initial angle of the parallel glass plate are explained, and experimental results with error analysis are presented to verify them.