Each row of two frames represents one snapshot-pair of laser on (on the right side) and laser off (on the left side) with unchanged configuration. One can see a clear increase from these pictures, proof that the laser accelerates the 20 mega electron volts electron beam in vacuum. Pictures of the beam momentum spread after the spectrometer taken with the laser off (left column) and the laser on (right column). The length of the beam image reveals the energy spread of the beam. The experiment recorded 30 shots. Twenty shots were high intensity and showed effects of the laser on/laser off difference. Four shot examples are shown here. Pictures are taken from spectrometer on Beam Line #1 at BNL-ATF.


Physicists demonstrate acceleration of electrons by laser in vacuum

February 28, 2013

(Phys.org)—Accelerating a free electron with a laser has been a longtime goal of solid-state physicists. David Cline, a distinguished professor in the UCLA Department of Physics and Astronomy, and Xiaoping Ding, an assistant researcher at UCLA, have conducted research at Brookhaven National Laboratory in New York and have established that an electron beam can be accelerated by a laser in free space.

This has never been done before at high energies and represents a significant breakthrough, Cline said, adding that it also may have implications for fusion as a new energy source.

In free space, a plane-wave laser is unable to accelerate an electron, according to the Lawson–Woodward theorem, posited in 1979. However, Yu-kun Ho, a professor at China’s Fudan University in Shanghai, and his research group have proposed a concept of what physicists refer to as the capture–acceleration scenario to show that an electron can be accelerated by a tightly focused laser in a vacuum.

In the capture–acceleration scenario, the diffraction from a tightly focused laser changes not only the intensity distribution of the laser but also its phase distribution, which results in the field phase velocity being lower than the speed of light in a vacuum in some areas.

Thus, a channel that overlaps features of both strong longitudinal electric field and low–laser-phase velocity is created, and electrons can receive energy gain from the laser. The acceleration effect increases along with increasing laser intensity, Cline said. This channel for electrons may be useful for other scientific endeavors, such as guiding an electron beam into a specific region of laser fusion applications, he said.

Read more: Physicists demonstrate acceleration of electrons by laser in vacuum — phys.org.

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