The Diocles laser at the University of Nebraska-Lincoln. Image: UNL

Physicists Made the Brightest Light Ever

The Diocles laser is as bright as one billion suns and could pave the way for next generation x-ray technology.

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Jun 26 2017, 3:00pm

The Diocles laser at the University of Nebraska-Lincoln. Image: UNL

A group of physicists at the University of Nebraska-Lincoln's Extreme Light Laboratory announced Monday that they have created the brightest light ever produced on Earth using Diocles, one of the most powerful lasers in the United States.

By firing this laser at individual electrons, the researchers found that past a certain threshold, the brightness of light will actually change an object's appearance rather than simply making it brighter.

"When we have this unimaginably bright light, it turns out that the scattering [of photons]—this fundamental thing that makes everything visible—fundamentally changes in nature," Donald Umstadter, a physicist at the University of Nebraska-Lincoln, said in a statement.

In order to appreciate what Umstadter and his colleagues have accomplished, consider the way light normally works. When photons from a light source such as the sun or a lightbulb strike an object, those photons interact with the electron clouds that surround the nuclei of the atoms that make up that object. More to the point, when photons strike these negatively charged particles, they are scattered with the same angle and energy which the photon possessed before the interaction with the electron. It is this scattering effect produced by photon-electron interactions that allow us to see objects.

In nature, an individual electron interacts with an individual photon pretty infrequently—about every four months, according to Umstadter. Moreover, the brightness of the light source doesn't affect the way the photons interact with the electrons. The photons will still retain their energy and angle after striking the electrons.

But as Umstadter and his colleagues found, this only holds true up to a certain threshold of light intensity. Beyond this threshold, ultrahigh-intensity light sources will cause the photon's angle and wavelength to change after striking the electron. The effect of this is that the object will actually change appearance, rather than just getting brighter.

In the experiment, Umstadter and his colleagues suspended electrons in helium and then hit these individual electrons with the Diocles laser. In nature, a single photon will interact with a single electron at a time. But in the University of Nebraska experiment, the researchers would bombard a single electron with roughly 1,000 photons during each laser pulse, which last for about 30 billionths of one millionth of a second.

When this high intensity laser pulse, which is one billion times brighter than the surface of the sun, strikes the electron, it causes it to behave differently. Rather than maintaining its regular "up-and-down" motion, the electron begins moving in a pattern that looks more like a figure eight. This new movement causes the photons to scatter differently than they would under natural circumstances, which is why it makes the object appear differently, rather than just getting brighter.

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When photons strike electrons in nature, the electrons emit their own photon as a result of the interaction. But when the researchers hit electrons with the Diocles laser, they found that the photon that was ejected absorbed the collective energy of the rest of the scattered photons from the laser. This imbued the ejected photon with the energy and wavelength of an x-ray, which has a smaller wavelength and greater energy than visible light.

The x-rays that are produced in this fashion have an extremely high amount of energy, and Umstadter and his colleagues think this could end up being applied in a number of ways. For starters, it could allow doctors to produce x-ray medical images on the nanoscale, which would allow them to detect tumors and other anomalies that regular x-rays might have missed.

Moreover, it could also be used for more sophisticated x-ray scanning at airports and other security checkpoints.

For now, however, this method of x-ray production remains highly experimental. Still, Umstadter and his colleagues are excited by the results, which added substantial new information to the fields of electrodynamics and optical physics.

"There were many theories, for many years, that had never been tested in the lab because we never had a bright enough light source to actually do the experiment," Umstadter said. "There were various predictions for what would happen, and we have confirmed some of those predictions."