An achromatic neutron lens

Neutrons provide exceptional insight into the structure and dynamics of materials, owing to their sensitivity to light elements, isotopic composition, magnetic moments, and high-penetration capabilities. Neutron sources produce beams that are polychromatic and have low brightness. Neutron optics provides a promising route to mitigate these challenges by guiding and focusing neutron beams, and to date, various types of neutron optics have been developed based on reflection, refraction, diffraction, and magnetism. Notably, compound refractive lenses and Fresnel zone plates have also been demonstrated for imaging and focusing applications, yet their severe chromatic aberration under polychromatic beams has prevented their widespread use and continues to limit progress towards true high-resolution neutron microscopy. Here, we demonstrate an achromatic neutron lens combining a compound refractive lens and a Fresnel zone plate. We experimentally verify its achromatic behaviour and compare its performance to a Fresnel zone plate. We employ the achromatic neutron lens to realise a full-field neutron microscope. This development overcomes the long-standing trade-off between flux and spatial resolution that constrains neutron imaging in a pinhole-based radiography geometry and establishes a pathway towards high-resolution neutron microscopy. We anticipate that this new class of neutron optics will advance a broad range of neutron methods that require or benefit from focused neutron beams.