Already the brightest light on Earth, the Diocles Laser at the University of Nebraska-Lincoln is also capable of accelerating electrons 1 trillion trillion times faster than a rocket blasting off into space.

While many think of light as the illumination of a dark room or the radiance from a midday sun, when concentrated into a laser beam, the extraordinary properties of light are put on full display.

"Light actually exerts a force," said Donald Umstadter, a professor of physics and astronomy who oversees UNL's Extreme Light Laboratory, where lasers are used to break new ground in physics.

Umstadter's team, led by senior research associate Grigory Golovin, recently proved that laser light is capable of pushing electrons in a new direction at incredible speeds — almost instantaneously.

It's the latest and most extreme example of how the forces created by light, while sounding like science fiction, are actually science fact.

Scientists have long theorized that light could be harnessed by mankind in applications such as a "light sail," advocated by the late physicist Stephen Hawking, as a way to propel spacecraft on long voyages without the need for fuel.

Pushed by light forces long enough, for years even, the spacecraft could theoretically achieve very high speeds that would be impossible through traditional jet propulsion.

Another application, currently used by scientists, implements the forces produced by light to trap and hold microscopic particles like "optical tweezers," or a kind of tractor beam seen in "Star Wars" or "Star Trek."

But both of those uses rely upon forces much smaller compared to the intensity of the Diocles Laser at UNL, named in honor of the inventor of the parabolic mirror more than 2,000 years ago.

"All the light you see is in the form of these electromagnetic waves, which are oscillating electric and magnetic fields," Umstadter said. "Up until now, in the other applications, the magnetic field was not involved in the force. In our case, it plays an equal role to the electric field, which leads to very strong forces."

Researchers at the Extreme Light Laboratory fired the Diocles Laser through helium gas. As the microscopic beam of light passed through the "sea of electrons" created by the helium, the force caused the electrons to oscillate at relativistic speeds, or at speeds comparable to the speed of light.

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Once the electrons began oscillating at relativistic speeds, the magnetic field also begin to act, intensifying the force being applied.

"We thought 'optical rocket' was an appropriate name to describe what happens," Umstadter said. "But an actual rocket is minuscule to the speed we can achieve with a laser."

Accelerating electrons to near the speed of light may help future researchers peel back the structure of matter, Umstadter said, in order to learn "what everything is made of at the highest resolution."

It also proves that electron accelerators used in radiation treatment for cancer patients or by technology companies to examine the quality of semiconductor chips can come in relatively compact and portable sizes.

Other universities and research sites, like the Stanford Linear Accelerator Center in California, have built electron accelerators in miles-long tubes, whereas the Diocles Laser is housed in a basement on UNL's City Campus.

The total energy produced in Behlen Hall might be smaller than the stadium-sized electron accelerators, but for its size, the energy produced is comparable, Umstadter said: "We basically shrunk their accelerator by 10,000 times."

This year's discovery marks the second breakthrough in less than a year for the nine-member Extreme Light Laboratory.

In 2017, the lab discovered that an intense pulse from the Diocles Laser 1 billion trillion times brighter than the sun forced electrons to scatter, creating a unique kind of X-ray.

That finding, which landed the team on the cover of "Nature Photonics" last December, could prove useful in low-radiation medical imaging, or for national security purposes, Umstadter said.

The Extreme Light Laboratory got a second home run this year with its National Science Foundation-funded electron acceleration study, which was published in the September edition of "Physical Review Letters."

"Like the football team, we also have dreams of national championships," Umstadter said. "For us, getting published in 'Physical Review Letters' is a national championship."

Reach the writer at 402-473-7120 or cdunker@journalstar.com.

On Twitter @ChrisDunkerLJS.


Higher education reporter

Chris Dunker covers higher education, state government and the intersection of both.

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