Donald Umstadter, head of the university's Extreme Light Laboratory, worked with colleagues in physics and astronomy to design an experiment in which pulses of light one billion times brighter than the surface of the sun were shot into an extremely tiny space. To facilitate the experiment, the research team fired up the lab's Diocles Laser, a room-sized assembly of optical equipment that can reach a peak power output greater than all the world's power plants combined.
The trick is that the laser produces bursts of light that only last a tiny fraction of a second.
“That makes high power, equivalent to a trillion light bulbs, but only for a very short amount of time — less than a trillionth of a second,” Umstadter said. “We then concentrate that power into a tiny spot, a millionth of a meter in size. That makes high intensity or brightness.”
By aiming the laser bursts at an intersecting stream of electrons, with precision down to a millionth of a meter, the researchers were able to observe how photons behave when striking a single electron.
It turns out that, at this level of brightness, the photons misbehave rather spectacularly. The high-energy illumination essentially knocks the electrons out of their usual alignment, scattering light in a fundamentally different way. The impact rattles the electrons into a figure-eight “quiver” pattern, shooting off additional photons at different angles, shapes, and wavelengths. The phenomenon, mathematically predicted in various theories, had never before been confirmed in the laboratory.
The team's research was funded by the US Air Force, US Department of Energy, the Department of Homeland Security's Domestic Nuclear Detection Office, and US and Chinese national science foundations. Thee findings are published in the journal Nature Photonics.
Under the ultra-bright light of the Diocles laser, however, scientists can actually see things that are otherwise invisible to the human eye.
“It is amazing,” Umstadter said. “The light's coming off at different angles, with different colors, depending on how bright it is. What it reveals for the first time is the motion of electrons oscillating in the light fields at nearly the speed of light. They oscillate in a different pattern than they do in normal light.”
As a practical matter, the new technique can generate three-dimensional images with unprecedented resolution and accuracy. The additional photons ejected from the illuminated electrons act like super-powered X-rays. Doctors could use this kind of imaging to spot tumors or microfractures that would otherwise be missed by standard X-ray machines.
The technology can also be used to map circuitry on the molecular level, which will be useful for manufacturers who are increasingly building semiconductors on the nanoscopic scale. The super x-ray properties could also be used at airport security checkpoints, to make sure that that laptop computer is really a laptop computer.
“The higher X-ray energies we produce can be used to see through thickly shielded materials, nearly a meter thickness of steel, for cargo inspection, or non-destructive testing and evaluation of critical components,” Umstadter said.
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