High-reflectivity (m=4) elliptical neutron focusing supermirror fabricated by numerically controlled local wet etching with ion beam sputter deposition

High-performance neutron-focusing supermirror devices with both high figure accuracy and high reflectivity are essential to effectively collect and focus a neutron beam on a sample without scattering loss. To fabricate these devices, numerically controlled local wet etching and ion beam sputter deposition techniques were developed for the figuring of an aspherical mirror substrate and for the deposition of NiC/Ti multilayers, respectively. By applying these techniques, a plano-elliptical supermirror with a clear aperture size of 90 mmx40 mm was fabricated to focus a cold neutron beam. Focusing performance and reflectivity were evaluated using a neutron reflectometer and a focusing gain of 4.4 and a reflectivity of 0.64-0.7 in the near-critical-angle region for m=4 were achieved.