Deriving the Size and Shape of the ALBA Electron Beam with Optical Synchrotron Radiation Interferometry Using Aperture Masks: Technical Choices

We explore non-redundant aperture masking to derive the size and shape of theALBA synchrotron light source at optical wavelengths using synchrotronradiation interferometry. We show that non-redundant masks are required due tophase fluctuations arising within the experimental set-up. We also show, usingclosure phase, that the phase fluctuations are factorizable into element-basederrors. We employ multiple masks, including 2, 3, 5, and 6 hole configurations.We develop a process for self-calibration of the element-based amplitudes(square root of flux through the aperture), which corrects for non-uniformillumination over the mask, in order to derive visibility coherences andphases, from which the source size and shape can be derived. We explore theoptimal procedures to obtain the most reliable results with the 5-hole mask,based on the temporal scatter in measured coherences and closure phases. Wefind that the closure phases are very stable, and close to zero (within 2^o).Through uv-modeling, we consider the noise properties of the experiment andconclude that our visibility measurements per frame are likely accurate to anrms scatter of ∼ 1%.