The problem of determining the phase ø of the complex degree of coherence γof a light beam from measurements of its modulus |γ|is considered. If a reference beam of light with an exactly known complex degree of coherence is available, then the phase ø may be determined from an additional experiment in which the two beams are superimposed.
C. L. MEHTA, "New Approach to the Phase Problem in Optical Coherence Theory," J. Opt. Soc. Am. 58, 1233-1234 (1968)