Construction of silicon neutron interferometers requires a perfect crystalsilicon ingot (5 cm to 30 cm long) be machined such that Bragg diffracting"blades" protrude from a common base. Leaving the interferometer bladesconnected to the same base preserves Bragg plane alignment, but if theinterferometer contains crystallographic misalignments of greater than about 10nrad between the blades, interference fringe visibility begins to suffer.Additionally, the parallelism, thickness, and distance between the blades mustbe machined to micron tolerances. Traditionally, interferometers do not exhibitusable interference fringe visibility until 30 $\mu$m to 60 $\mu$m of machiningsurface damage is chemically etched away. However, if too much material isremoved, the uneven etch rates across the interferometer cause the shape of thecrystal blades to be outside of the required tolerances. As a result, theultimate interference fringe visibility varies widely among neutroninterferometers that are created under similar conditions. We find thatannealing a previously etched interferometer at $800^\circ \mathrm{C}$dramatically increased interference fringe visibility from 23 % to 90 %. TheBragg plane misalignments were also measured before and after annealing usingneutron rocking curve interference peaks, showing that Bragg plane alignmentwas improved across the interferometer after annealing. This suggests thatcurrent interferometers with low fringe visibility may be salvageable and thatannealing may become an important step in the fabrication process of futureneutron interferometers, leading to less need for chemical etching and larger,more exotic neutron interferometers.
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