Two-dimensional Light Beam Shape Characterization using Interferometric Closure Amplitudes

We introduce a novel technique using closure amplitudes, inspired by radio interferometry, to determine with high angular resolution the two-dimensional profile of a light beam using an interferogram from a non-redundantly masked aperture. Previous techniques have required multiple interferograms or accurate estimates of the non-uniform illuminations across the aperture. In contrast, our method using closure amplitudes avoids the need to estimate the aperture illuminations while determining the two-dimensional beam shape from a single interferogram. The invariance of closure amplitudes to even time-varying aperture illuminations makes it suitable to longer averaging intervals, with potential to reducing data rates and computational overheads. By using data from the ALBA synchrotron light source to validate the method and its results against existing methods, this paper represents the first real-world application of closure amplitudes to directly determine the light beam's profile using optical interferometry in the high angular resolution regime.