Objective methods of measuring the path difference of polarized rays

Several objective methods of measuring the path difference of polarized rays are analyzed: the photometric analysis method, the Senarmont and Tardy modulation methods, Edel'shtein's method. Senarmont's simultaneous measurement of the path difference in two monochromes, having a working wavelength and an auxiliary wavelength, with the continuous modulation of the light polarization state was found to be the most effective method. Information about the sign of the path difference and about the whole number of interference orders in almost any range of variation of the path difference can be obtained from the values of the angles, characterizing the fractional part of the interference orders. If path difference compensators are needed in photoelectric instruments, it is advisable to use compensators in the form of phase wave plates of different thickness with third wave plates. It is also desirable to determine the direction of the principal axes over a broad spectral interval at the largest possible d/B values, where d = the diameter of the circular diaphragm and B is the arbitrary distance between interference fringes.