Measurement of interferograms perturbed by random phase fluctuations

The measurement of interferograms which have been subjected to random phase fluctuations, as well as additive noise, is considered in the cases of (1) signals sufficiently strong to permit phase tracking, and (2) long averaging of weak signals. In the first case, it is shown that averaging of the in-phase and quadrature components, in order to reduce additive noise, causes a decorrelation noise power which increases with averaging time T, peaks and then decreases with T^-1. Averaging of these components also increases the probability of ±2π ambiguities. Optimum averaging times and criteria for minimizing the likelihood of phase ambiguities are presented. The possibility of obtaining reliable phase information from averaging times much longer than the coherence time of the fluctuations is shown.