A billion suns: Bright light illuminates healthcare

04 July 2017

Interview with

Donald Umstradter, University of Nebraska-Lincoln

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When light particles, called photons, hit the electrons in the atoms that things are made of, the light is scatted. And this is the reason why things are actually visible. But now scientists at the University of Nebraska-Lincoln have created the brightest light on Earth and found that at these energies when substances are illuminated something exciting happens that could make a massive contribution to healthcare and security. Izzie Clarke spoke to Donald Umstradter about the light source he’s made and what happens when it illuminates something...

Donald - It’s about a billion times brighter than the surface of the Sun. In terms of power, it’s got the power of all the Earth’s electrical grid but it’s only on for a very short time. To make high brightness you need to have that power of light focussed to a very small spot. We focussed it to an area that is only about a millionth of a metre in diameter. We’re producing the most photons per unit area that has ever been produced on Earth.

Izzie - Donald and his team amplified short pulses of light up to high energy in a laser system. That makes this light of a high power which is equivalent to a trillion light bulbs. But that only occurred for a very short amount of time. Concentrating that power into a tiny spot makes the light incredibly bright with high intensity. Next step was to aim this extremely bright light at a minute target - an electron… But how?

Donald - What we’re using is a mirror that has a curved surface. We call it a parabolic reflector that allows the rays to be focused at some distance away.

Izzie - These parabolic mirrors are similar to those used in radio telescopes. Looking at how light interacts with matter is a fundamental part of physics. Under typical conditions, when the light from a bulb or the Sun strikes a surface, it’s scattered by an electron, and this is what makes vision possible.

With light of a standard brightness, the electron will scatter the photon at the same angle and energy it had before striking the electron, regardless of how bright that light might be. Yet, Donald’s team found that above a certain threshold, the laser’s brightness altered the properties of the scattered light…

Donald - The electron responded to this brighter light by emitting a new light that had much more energy than the original light. The energy was high enough that we would call it an X-ray.

Izzie - That phenomenon stemmed partly from a change in the electron’s movement, which abandoned it’s usual up and down motion in favour of a figure eight pattern. It was found that the ejected photon had absorbed the collective incoming photon energy granting it the energy and wavelength of an X-ray. Whilst this theory had existed for decades, this behaviour in light had never been documented. Let’s break this down a bit more…

Imagine you had a dimmer switch in your kitchen. At low brightness your table would appear dark but, as you turn up the switch, it gets brighter and more visible. This is what happens when we use standard light to see. But, hypothetically, if your dimmer switch was controlling this ultra bright light, it’s as though your table would have suddenly disappeared. The light waves that are being scattered back from the table have turned into X-rays, which we cannot see. But, and X-ray scanner can, of course…

Donald - The typical X-ray that you get at a hospital is more like a light bulb than it is a laser and so produces all frequencies of  X-rays, and it produces them over all different angles and most of those X-rays are wasted. X-rays can also give you cancer and so the dosage has to be kept below a certain level. It turns out that the X-rays we produce, produce good quality images with ten times lower dose, and so they’re much safer and better quality.

Izzie - X-rays are also used within security. Is there the possibility that we could X-rays to improve security as well?

Donald - We have shown that the X-rays we are producing this way can penetrate through very thick steel and still get a very good image of what is hidden behind that steel. There’s a big concern that nuclear materials could be transported through cargo containers and so it’s very important to be able to inspect cargo containers for such threats in a rapid and non-destructive way, and that’s what we’ve demonstrated with our X-ray source.

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