Laser Sparks New Behavior in Light

By focusing laser light to a brightness one billion times greater than the surface of the sun, physicists at the University of Nebraska-Lincoln have observed changes in a vision-enabling interaction between light and matter. The changes produced unique x-ray pulses with the potential to generate extremely high-resolution imagery useful for medical, engineering, scientific and security purposes.

A scientist at work in the Extreme Light Laboratory at the University of Nebraska-Lincoln, where physicists were able to change the way photons scatter from electrons. Courtesy of University of Nebraska-Lincoln.

The university’s Extreme Light Laboratory fired their Diocles laser at helium-suspended electrons to measure how the laser’s photons scattered from a single electron after striking it.

Though previous laser-based experiments had scattered a few photons from the same electron, the University of Nebraska-Lincoln team managed to scatter nearly 1000 photons at a time. At the ultrahigh intensities produced by the laser, both the photons and electron behaved much differently than expected.

"When we have this unimaginably bright light, it turns out that the scattering — this fundamental thing that makes everything visible — fundamentally changes in nature," said Donald Umstadter, the Leland and Dorothy Olson professor of physics and astronomy.

A rendering of how changes in an electron's motion (bottom view) alter the scattering of light (top view), as measured in a new experiment that scattered more than 500 photons of light from a single electron. Previous experiments had managed to scatter no more than a few photons at a time. Courtesy of Extreme Light Laboratory/University of Nebraska-Lincoln.

A photon from standard light typically scatters at the same angle and energy it did before striking the electron, regardless of how bright its light might be. Yet Umstadter's team found that, above a certain threshold, the laser's brightness altered the angle, shape and wavelength of the scattered light.

"So it's as if things appear differently as you turn up the brightness of the light, which is not something you normally would experience," said Umstadter. "An object normally becomes brighter, but otherwise, it looks just like it did with a lower light level. But here, the light is changing the object's appearance. The light's coming off at different angles, with different colors, depending on how bright it is."

University of Nebraska-Lincoln physicists obtained this high-resolution x-ray of a USB drive. The image reveals details not visible with ordinary x-ray imaging. Courtesy of Extreme Light Laboratory/University of Nebraska-Lincoln.

That phenomenon stemmed partly from a change in the electron, which abandoned its usual up-and-down motion in favor of a figure-8 flight pattern. As it would under normal conditions, the electron also ejected its own photon, which was jarred loose by the energy of the incoming photons. The researchers found that the ejected photon absorbed the collective energy of all the scattered photons, granting it the energy and wavelength of an x-ray.

The research has been published in the journal Nature Photonics (doi:10.1038/nphoton.2017.100).