On neutron holography, neutron interferometry, and neutron orbital angular momentum

In Opt. Express 24, 22528 (2016)10.1364/OE.24.022528, D. Sarenac et al. reported neutron holography using a Laue crystal interferometer and a spiral phase plate, interpreting the resulting interference pattern as a hologram reconstructing neutron beams carrying orbital angular momentum (OAM). However, this interpretation is highly questionable: the interferometer's markedly unequal lateral coherence lengths are far too small and, moreover, should have produced an asymmetric pattern, which was not observed. Our simulations demonstrate that the reported images can be fully explained as conventional interference patterns without invoking OAM. Furthermore, we highlight the inherent challenges of using crystal interferometry for holography and question whether neutron OAM states are necessary - or even sufficient - to account for the observed results.