High-performance Kirkpatrick-Baez supermirrors for neutron milli- and micro-beams

High-performance Kirkpatrick-Baez (KB) neutron supermirror optics can nondispersively image neutrons to small spots. Ray tracing finds that under many conditions, KB mirrors work near the theoretical limit set by source brilliance and can deliver orders of magnitude greater intensities than is possible with conventional (nonfocusing) neutron optics. In general, KB neutron supermirrors are preferred when the required beam size at the sample is small and when the distance between the optics and the sample is not small. Waveguides with beam definings slits are preferred for very short wavelengths, for big beams and when the slits can be placed very close to the sample. For example, for λ ∼ 0.1 nm, if the distance from the last optical element to the sample is ∼100 mm, almost two orders of magnitude greater intensity can be focused onto a 100 μm spot with M = 3 KB supermirrors than with a beam guide and symmetric slits. This is independent of whether the beam guide collimates or condenses the beam so long as without slits the beam is larger than the acceptable beam size at the sample. We describe the ray tracing and phase space arguments that support the use of KB supermirrors for producing intense small beams and describe the performance of a prototype KB device which achieved a 89 μm × 90 μm focus. We briefly describe even more advanced methods that can increase the beam divergence on the sample while maintaining a small beam.