A critical look at the source characteristics used for time varying fringe interferometry

Interference fringes are registered by detectors. All detectors absorb energy from a single or multiple superposed fields through the process of “square modulus” of the sum of the complex amplitudes. The detected energy becomes proportional to the total relative phase difference for all the superposed fields. The process creates ambiguity in discerning the effects due to frequency and phase modulations. We underscore that fringe detection being a physical interaction process between superposed fields and detecting molecules (including beam splitter boundary), the dipolar properties of atoms and molecules should be used to help us discern the effects due to frequency and phase modulations. We traditionally accept that orthogonally polarized light beams do not “interfere”. Or, light beams of different frequencies are “incoherent” to each other; but we have highly developed heterodyne interferometry for which the wave fronts of the superposed beams must be matched. Yet, we do not explicitly recognize the roles of the molecules of detectors and beam splitters that really carry out the real functions. Besides, understanding the various processes behind their dipolar response can help us innovate more precision interferometric techniques. As for examples: (i) How precisely the polarization should be parallel to produce perfect visibility fringes? (ii) How precisely equal the optical frequencies of superposed beams should be to create perfectly steady-state energy re-direction by a beam splitter in an interferometer with collimated and collinear beams. (iii) How small the wave front mis-match can be tolerated to produce perfect heterodyne fringes while superposing beams of different frequencies?