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NIST Scientists Use Neutrons to Develop Holograms

Interference pattern created by neutron holography. Credit: NIST

A team of scientists from the National Institute of Standards and Technology (NIST) have used neutron beams for the first time to develop holograms of huge solid objects, exhibiting details about their interiors in a manner that has never been achieved by ordinary laser light-based visual holograms.

Holograms, flat images that change based on the viewer’s perspective highlighting the fact that they are three-dimensional objects, owe their striking potential to an interference pattern. All matter, such as photons and neutrons of light, can act like rippling waves with valleys and peaks. Just like a water wave that hits a gap between the two rocks, a wave can come apart and then re-combine to develop information-rich interference patterns.

An optical hologram is produced by shining a laser at an object. Instead of just photographing the light reflected from the object, a hologram is produced by recording how the reflected laser light waves hinder each other. The patterns obtained, according to the phase differences of the waves, or relative positions of their valleys and peaks, comprise of more details regarding the appearance of an object when compared to what a simple photo does, though they do not usually reveal much about its hidden interior.

Hidden interiors are the ones explored by neutron scientists. Neutrons excel at penetrating metals and various other solid things, enabling neutron beams to be useful for scientists who produce a new substance and want to examine its properties. Limitations found in neutrons highlight that they are not very good for producing visual images and that neutron experiment data is generally expressed as graphs that would look at home in a high school algebra textbook.

This data typically provides details about how a substance is produced on average, fine if they are interested in knowing more about an object constructed from a bunch of repeating structures such as a crystal. However, it is not good if they just want to know the details about only one particular bit of it.

The scientists have discovered a way to acquire the best of both the worlds.

Their earlier work, carried out at the NIST Center for Neutron Research (NCNR), focused on passing neutrons through an aluminum cylinder that had a small spiral staircase carved into one of its circular faces. A twist to the neutron beam was caused by the shape of the cylinder, but the scientists also observed that the individual neutrons of the beam changed phase based on what section of the cylinder they passed through: greater phase shift took place when the thickness of the section increased.

The team finally realized that this was the information they needed to develop holograms of objects’ innards, and this method has been described in their new paper.

This discovery will not change anything about interstellar chess games, but it instead adds to the palette of techniques scientists have to investigate solid materials. The team demonstrated that all that is needed is a beam of neutrons and an interferometer, a detector used for measuring interference patterns, to develop direct visual representations of an object and present details about particular points within it.

Other techniques measure small features as well, only they are limited to measuring surface properties. This might be a more prudent technique for measuring small, 10-micron size structures and buried interfaces inside the bulk of the material.

Michael Huber, Physical Measurement Laboratory, NIST

The work was a multi-institutional collaboration that included scientists from NIST and the Joint Quantum Institute, a research partnership of NIST and the University of Maryland, as well as North Carolina State University and Canada’s University of Waterloo.

Neutron Holography Video

These animations, even though they are not holograms themselves, explain data that established the fact that neutron beams, rather than the typical laser light, can be used to produce holograms of solid objects, in this case a small aluminum plate with a spiral carved into one of its faces.

Animation of neutron scanning data, demonstrating that scientists can use neutron beams to create holograms instead of the usual laser light.

The first animation demonstrates what happens when one slowly moves back from the plate, which stands out as the bright circle in the center. Just near the end, fainter circles are observed at bottom and top (developed by interference patterns in the neutron beams) that generally exhibit the outlines of the spiral surface of the plate.

Animation of neutron scanning data, demonstrating that scientists can use neutron beams to create holograms instead of the usual laser light.

Transmitting the neutron beam through successively thicker portions of the spiral plate develops the interference data used for producing the second animation below, whose “fork” grows greater numbers of tines at right based on an increase in the thickness of the plate. Integrating these data with neutron measurements can develop 3D holograms, which could allow scientists to visually interpret the neutron scan results in an effortless manner.

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