The device uses lasers to accelerate electrons along an etched channel.

In a full-scale particle accelerator, electrons fly along a kilometers-long path as microwaves bombard them, boosting the particles to near light speed. Such a high-energy electron beam, produced at facilities such as California’s SLAC National Accelerator Laboratory, enables a variety of experiments, including capturing extremely detailed images and probing the structures of molecules. But particle accelerators are expensive, require scientists to travel from locations all over the world and cannot accommodate all the researchers who submit requests to book time. To make these devices more accessible, a team at Stanford University developed a laser-driven particle accelerator that fits on a tiny silicon chip—and that could eventually be scaled up to produce a beam with as much energy as SLAC’s.

“The idea of using lasers in accelerators goes all the way back to the year the laser was invented, 1960,” says Robert Byer, a Stanford researcher who has been working on this concept since 1974. Lasers produce electromagnetic waves with much shorter wavelengths than the microwaves used in a full-scale accelerator, which means they can accelerate electrons moving through a much smaller space. “The size of these devices is uncannily small,” Byer says. The electrons in the new accelerator, for example, travel along a channel that is about three one-thousandths of a millimeter wide—around half the width of a human red blood cell.

Although laser-driven devices can accelerate electrons in a much smaller space than full-scale accelerators, they also require much greater precision to line up the laser and the electrons in the right way, so the light waves push the particles in the correct direction with as much energy as possible. “You not only have to demonstrate the ability to couple the laser light to the electrons in these very small structures, but you have to generate the electrons and have them also be transmitted by the channel,” Byer explains. In 2013 two research groups, one at Stanford and other U.S. institutions and another in Germany, independently managed to accelerate electrons with lasers. But these proof-of-concept prototypes required separate devices to generate the electrons, and they would be difficult to manufacture in bulk using existing techniques.

Image Credit:  Neil Sapra