Two-dimensional light beam shape characterization using interferometric closure amplitudes

We introduce a 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 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 for longer averaging intervals, with the potential to reduce 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, to our knowledge, 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.