Speeding up Electronics With Light

Light pulses generate Multi-PHz electric current in bulk solids. The emitted extreme ultraviolet radiation allows scientists to record these electric currents in real time. (Source: Attoelectronics, MPQ)

Light pulses generate Multi-PHz electric current in bulk solids. The emitted extreme ultraviolet radiation allows scientists to record these electric currents in real time. (Source: Attoelectronics, MPQ)

The perfor­mance of modern electronic devices such as computers or mobile phones is dictated by the speed at which electric currents can be made to oscillate inside their elec­tronic circuits. The shrinkage of basic elec­tronic elements, such as tran­sistors, to smaller and smaller dimensions over the last decades has allowed the development of ever-faster elec­tronic devices like the ones used in everyday life. However, this metho­dology of speeding up elec­tronics is now rapidly approaching its ultimate limits; devices are becoming nearly as small as only a few atoms and con­ventional principles of elec­tronic tech­nology hardly apply in these dimensions, calling for new routes to be discovered.

A team of scientists led by Elef­therios Gouliel­makis, head of the “Atto­electronics” research group at the Max Planck Institute of Quantum Optics, have been able for the first time to use lasers to create electric currents inside solids which exceed the frequency of visible light by more than ten times. The scientists used silicon dioxide, a material that is typically used as an insulator in the elec­tronic industry aiming to stop rather than to allow electric currents in its bulk. However, when this material was exposed to intense lasers the con­ductivity was increased by more than 19 orders of magnitude enabling new oppor­tunities for modifying the pro­perties of material on an ultrafast time scale.

“The possi­bility of having light replace conven­tional sources of elec­tricity, such as batteries in order to generate electric currents inside solid materials, like those used in the electronic industry, has captured the imagi­nation of scientists for more than a century,” explained Elef­therios Gouliel­makis. In his Nobel lecture, Karl Ferdinand Braun, the inventor of the first solid-state elec­tronic device — the recti­fying diode — alluded to his unsuc­cessful attempts to observe currents in solid materials by shining light on them. “Today, however, as control of matter with lasers is rapidly advancing and the capability to measure light fields with ever finer precision has turned to reality, the idea of using lasers for guiding the motion of electrons inside solids such as to create high frequency elec­tronic currents is rapidly gaining momentum,” Goulielmakis adds.

Conven­tional electronic tech­niques can neither generate nor capture such fast electric currents. Scientists in the Atto­electronics group used another approach. “To generate the currents we used lasers, as they can set electrons in solids into an extremely fast oscil­latory motion,” explained Manish Garg, a graduate student and leading author of this work. But why can lasers bring such an advance? In conven­tional circuits, electrons are pushed by the electric field of standard electric sources, such as batteries to perform oscillations. Even though all electrons initially follow the force of the battery fields, they even­tually collide with other slower moving particles such as atoms or ions and lose their synchrony with each other. Intense light fields can push electrons extremely fast. They can perform their oscillations and create currents before any other particle in the solid has the oppor­tunity to move. “To measure this fast electronic motion, we used optical techniques. Instead of directly measuring the electric currents, we measured the oscillations of the extreme ultra­violet radiation emitted as the electrons cohe­rently oscil­late inside silicon dioxide to generate this radiation,” he adds.

The detected electric currents are approxi­mately one million times faster than those widely used in a modern computer processor. “Although our focus is to explore the physical limits, our study may open the way of speeding up future elec­tronic devices by a million times in the years to come,” said Minjie Zhan a researcher in the group of Gouliel­makis. “Our work opens up the route to realizing coherent elec­tronics in bulk materials, an idea earlier concei­vable only for isolated molecules. As electrons move cohe­rently they also generate light which is the key element of pho­tonics. For this reason it may soon allow us to unify two impor­tant areas of modern science and techno­logy, elec­tronics and photonics,” Goulie­makis adds. (Source: MPQ)

Reference: M. Garg et al.: Multi-petahertz electronic metrology, Nature 538, 359 (2016); DOI: 10.1038/nature19821

Link: ERC Research Group Attoelectronics, Max Planck Institute of Quantum Optics, Garching, Germany

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