  Neutron scattering is a well-established tool for the investigation of the
static and dynamic properties of condensed matter systems over a wide range of
spatial and temporal scales. Many studies of high interest, however, can only
be performed on small samples and typically require elaborate environments for
variation of parameters such as temperature, magnetic field and pressure. To
improve the achievable signal-to-background ratio, focusing devices based on
elliptic or parabolic neutron guides or Montel mirrors have been implemented.
Here we report an experimental demonstration of a nested mirror optics (NMO),
which overcomes some of the disadvantages of such devices. While even simpler
than the original Wolter design, our compact assembly of elliptic mirrors
images neutrons from a source to a target, minimizing geometric aberrations,
gravitational effects and waviness-induced blurring. Experiments performed at
MIRA at FRM-II demonstrate the expected focusing properties and a beam
transport efficiency of 72 % for our first prototype. NMO seem particularly
well-suited to i) extraction of neutrons from compact high-brilliance neutron
moderators, ii) general neutron transport, and iii) focusing and polarizing
neutrons. The phase space of the neutrons hitting a sample can be tailored
on-line to the needed experimental resolution, resulting in small scattering
backgrounds. As additional benefits, NMO situated far away from both the
moderator and the sample are less susceptible to radiation damage and can
easily be replaced. NMO enable a modular and physically transparent realization
of beam lines for neutron physics similar to setups used in visible light
optics.
