The history of the development of methods and interference devices for measuring small optical phase differences (overview)

Methods of interferometry, which are used to measure very small phase differences, are considered. in fundamental and applied problems. It is shown that the first improvements in interferometric methods for measuring small phase differences for recording various physical phenomena in the second half of the XIX – early XX centuries. carried out by I.A. Fizeau, A.A. Michelson, E. Morley, Lord Rayleigh, D.C. Miller and J.M. Sagnac. It was also shown that the most sensitive method of modulation interferometry was created in the period 1949–1952. Soviet radiophysicists A.A. Andronov, I.L. Berstein and G.S. Gorelik. It is noted that the modulation interferometry method could be implemented even in 1914 with a photocell on an external photoelectric effect, or in 1923 with a photocell on internal photoelectric effect (photodiode). However, then professional opticians used traditional methods for measuring small phase differences, and radiophysics as a science was just beginning its formation. It is shown that the methods of electrical and photoelectric harmonic analysis developed in late XIX – early XX centuries could find successful application in interferometry, but by that time, when they could find practical use, they were almost completely forgotten.