The key to the design of the neutron microscope is the Wolter mirror, similar in principle to grazing incidence mirrors used for x-ray and gamma-ray telescopes.
When a neutron grazes the surface of a metal at a sufficiently small angle, it is reflected away from the metal surface at the same angle. When this occurs with light, the effect is called total internal reflection. However, owing to the way neutrons interact with the electrons in a metal, it would be better to call this total external reflection – the neutrons refuse to enter the material. Fortunately, the critical angle for grazing reflection is large enough (a few tenths of a degree for thermal neutrons) that a curved mirror can be constructed. Given curved mirrors, an optical system that creates an image can be made. The figure below shows a cartoon of a four power neutron microscope after the MIT design.