A micrometre-sized device that produces light by firing a beam of electrons over a slab of crystal could be used to build tiny particle accelerators and X-ray machines. Such chip-sized devices could be manufactured more quickly, cheaply and compactly than current particle accelerators.
Built by Yi Yang at the University of Hong Kong and his colleagues at the Massachusetts Institute of Technology, the new device consists of a special piece of silicon called a photonic crystal, a modified scanning electron microscope that fires a beam of electrons over it and a device that detects the emitted light. The set-up takes advantage of the electromagnetic fields that surround electrons as they move, which can make charged particles within a nearby material – in this case, the photonic crystal – become excited and emit light.
From mathematical models, the researchers knew that they could enhance the interactions between the crystal and the electrons by adding a pattern to the former, so they etched a grid of circular indentations, each about 100 nanometres wide, into it. Light and electrons don’t normally interact much, but engineering the energy and momentum of the light to match that of the electrons allows for unusually large interactions between the two. This matching method could eventually enhance light emissions up to a million times, says Yang.
That light has many potential uses, from spectroscopy, in which the light helps scientists learn about the internal structure of different materials, to light-based communication.
Notably, it can be used to make tiny particle accelerators, says Peter Hommelhoff at the University of Erlangen-Nuremberg in Germany. Researchers could use intense light pulses to accelerate particles instead of hitting them with microwaves, as is more common, he says.
Thomas Krauss at the University of York in the UK says the new device may not only be a step toward tiny particle accelerators but also toward smaller X-ray machines. X-rays are essentially light waves with wavelengths too short for us to see. By adapting the silicon pattern and the speed of the electrons in the device, it might be possible to change the wavelength of emitted light to X-rays.
“When you get an X-ray at your doctor, it’s a big beast of a machine. Now we can imagine doing it with a little light source, on a chip,” he says. That could make X-ray technology more accessible for small or remote medical facilities or make it portable for use by first responders in an accident.