# The photo-neutronrefractive effect

## TL;DR

This paper explores the photo-neutronrefractive effect, where certain materials change their neutron refractive index upon light exposure, and discusses experimental progress in creating neutron diffraction gratings and interferometers.

## Contribution

It introduces the concept of photo-neutronrefractive materials, presents experimental results on photopolymers and crystals, and advances neutron optical device development.

## Key findings

- Development of light-induced neutron diffraction gratings
- Construction of a cold neutron interferometer
- Survey of experimental results on photo-neutronrefractive materials

## Abstract

Since its discovery in 1966, the photorefractive effect, i.e. the change of the refractive index upon illumination with light, has been studied extensively in various materials and has turned out to play a key role in modern optical technologies like photonics. This article focuses on substances that change their refractive index for neutrons when irradiated with light. In analogy to light optics, we call them photo-neutronrefractive. After a short introduction to the relevant concepts of neutron optics, two materials exhibiting that effect, a photopolymer and an electrooptic crystal, are presented. Further, we discuss the the progress made concerning the development of creating light-induced gratings for neutron diffraction, which culminated in the setup of an interferometer for cold neutrons. Experiments performed on photo-neutronrefractive materials are surveyed and the variety of corresponding results obtained is presented, including a discussion of their impact on material science, neutron optics, and the foundations of physics.