The generation of neutron orbital angular momentum

Orbital angular momentum (OAM) beams of light and matter have several interesting properties that make them prime candidates as probes of chiral and textured condensed matter systems. We present two neutron spin echo experiments that demonstrate the generation of neutron OAM, one using magnetic Wollaston prisms (MWPs) and the other using a 2D array of silicon forked diffraction gratings (FDGs). MWPs generate OAM by using strong magnetic fields paired with high-temperature superconducting films to ensure sharp transitions between the field regions. In addition to OAM, MWPs in the 2D spin-echo modulated small-angle neutron scattering (SEMSANS) configuration also produce high-polarization spin textured neutron beams. We have demonstrated the ability to produce a wide variety of spin textures, and from these textures we can indirectly verify the production of neutron OAM. On the other hand, FDGs are non-magnetic and so can be used with techniques such as spin-echo small-angle neutron scattering (SESANS) that require non-depolarizing samples. We have demonstrated the production of OAM from FDGs using radio-frequency neutron spin flippers with SESANS, which also showed that SESANS can be used as a direct probe of topological structures and defects in materials. These experiments show that both MWPs and FDGs can generate high-fidelity states of neutron OAM which may have future application in the measurement of spin-textured and topological materials.