Scientists test upper limits of electron speed

The fastest electronic devices currently send information at speeds of several gigahertz, a billion oscillations per second. Some fiber-optic cables feature frequencies approaching a terahertz, a thousand billion oscillations.

But the need for speed is neverending, and researchers are beginning to experiment with how technology might move information-carrying electrons even faster. The next benchmark is the petahertz, a thousand times faster than the fastest fiber-optic cables.

Recently, researchers at ETH Zurich tested how electrons react to near-petahertz fields.

The scientists initiated the brief near-petahertz field by blasting a tiny diamond with a laser. They measured the reactions of the electrons by simultaneously flashing a pulse of ultraviolet light through the diamond.

The altered absorption of the light waves served as proof the electrons were uniquely excited by the laser-induced electric field. But to really understand what was happening inside the diamond, the scientists needed to build a computer model.

"The advantage of the simulations compared to the experiment, however, is that several of the effects that occur in real diamond can be switched on or off," Matteo Lucchini, a postdoctoral researcher at ETH, said in a news release. "So that eventually we were able to ascribe the characteristic absorption behavior of diamond to just two such energy bands."

The change in optical absorption of a semiconductor when an electric field is applied is known as the Franz-Keldysh effect.

The experiment -- detailed in the journal Science -- marks the first time the Franz-Keldysh effect has been observed as such extreme electronic frequencies.

"The fact that we could still see that effect even at petahertz excitation frequencies confirmed that the electrons could, indeed, be influenced at the speed limit of the laser field," concluded Lukas Gallmann.