Effective a posteriori Co-Phasing of Interferometric Fringe Data

We have recently shown that a posteriori co-phasing of multi-spectral interferograms was possible.(1) In this contribution, we extend our approach so that it can be applied to actual data as provided by AMBER(2) or MATISSE instruments. The main advantage of the proposed post-processing technique is that it requires no modifications of the instruments and yields interferometric observables with higher SNR and much fewer unknowns (in particular for the Fourier phase) than conventional measurements. In order to perform the co-phasing of a complete sequence of interferograms, we jointly estimate a global phase template and the frame dependent optical path errors due to the turbulence. We show that this strategy is effective for very low SNR data. We assess the effectiveness of our method on simulated and actual AMBER data. We also compare the lowest SNR that can be achieved to the theoretical bounds and estimate the gain in sensitivity compared to usual interferometric data.