December 06, 2012

Laser Pulse Controlled Petahertz Transistors could become 10 thousand times faster than todays transistors

A discovery that promises transistors – the fundamental part of all modern electronics – controlled by laser pulses that will be 10,000 faster than today’s fastest transistors has been made by a Georgia State University professor and international researchers.

There are three basic types of solids: metals, semiconductors, used in today’s transistors, and insulators – also called dielectrics.

Dielectrics do not conduct electricity and get damaged or break down if too high of fields of energy are applied to them. The scientists discovered that when dielectrics were given very short and intense laser pulses, they start conducting electricity while remaining undamaged.

The fastest time a dielectric can process signals is on the order of 1 femtosecond – the same time as the light wave oscillates and millions of times faster than the second handle of a watch jumps.

Dielectric devices hold promise to allow for much faster computing than possible today with semiconductors. Such a device can work at 1 petahertz, while the processor of today’s computer runs slightly faster than at 3 gigahertz.

“Now we can fundamentally have a device that works 10 thousand times faster than a transistor that can run at 100 gigahertz,” Stockman said. “This is a field effect, the same type that controls a transistor. The material becomes conductive as a very high electrical field of light is applied to it, but dielectrics are 10,000 times faster than semiconductors.”


Simultaneous attosecond absorption and streaking spectroscopy.

Nature - Optical-field-induced current in dielectrics



At one time, scientists thought dielectrics could not be used in signal processing – breaking down when required high electric fields were applied. Instead, Stockman said, it is possible for them to work if such extreme fields are applied at a very short time.

In a second paper also published online Dec. 5 in Nature, Stockman and his fellow researchers experimented with probing optical processes in a dielectric – silica – with very short extreme ultraviolet pulses. They discovered the fastest process that can fundamentally exist in condensed matter physics, unfolding at about at 100 attoseconds – millions of times faster than the blink of an eye.

The scientists were able to show that very short, highly intense light pulses can cause on-off electric currents – necessary in computing to make the 1s and 0s needed in the binary language of computers -- in dielectrics, making extremely swift processing possible.


Schematic of the experimental set-upforthedetection of light-field-induced photocurrents at a metal-dielectric-metal nanojunction.

ABSTRACT - The time it takes to switch on and off electric current determines the rate at which signals can be processed and sampled in modern information technology. Field-effect transistors are able to control currents at frequencies of the order of or higher than 100 gigahertz, but electric interconnects may hamper progress towards reaching the terahertz (10^12 hertz) range. All-optical injection of currents through interfering photoexcitation pathways or photoconductive switching of terahertz transients has made it possible to control electric current on a subpicosecond timescale in semiconductors. Insulators have been deemed unsuitable for both methods, because of the need for either ultraviolet light or strong fields, which induce slow damage or ultrafast breakdown respectively. Here we report the feasibility of electric signal manipulation in a dielectric. A few-cycle optical waveform reversibly increases—free from breakdown—the a.c. conductivity of amorphous silicon dioxide (fused silica) by more than 18 orders of magnitude within 1 femtosecond, allowing electric currents to be driven, directed and switched by the instantaneous light field. Our work opens the way to extending electronic signal processing and high-speed metrology into the petahertz (10^15 hertz) domain.

25 pages of supplemental material

Nature - Controlling dielectrics with the electric field of light

The control of the electric and optical properties of semiconductors with microwave fields forms the basis of modern electronics, information processing and optical communications. The extension of such control to optical frequencies calls for wideband materials such as dielectrics, which require strong electric fields to alter their physical properties. Few-cycle laser pulses permit damage-free exposure of dielectrics to electric fields of several volts per ångström and significant modifications in their electronic system. Fields of such strength and temporal confinement can turn a dielectric from an insulating state to a conducting state within the optical period. However, to extend electric signal control and processing to light frequencies depends on the feasibility of reversing these effects approximately as fast as they can be induced. Here we study the underlying electron processes with sub-femtosecond solid-state spectroscopy, which reveals the feasibility of manipulating the electronic structure and electric polarizability of a dielectric reversibly with the electric field of light. We irradiate a dielectric (fused silica) with a waveform-controlled near-infrared few-cycle light field of several volts per angström and probe changes in extreme-ultraviolet absorptivity and near-infrared reflectivity on a timescale of approximately a hundred attoseconds to a few femtoseconds. The field-induced changes follow, in a highly nonlinear fashion, the turn-on and turn-off behaviour of the driving field, in agreement with the predictions of a quantum mechanical model. The ultrafast reversibility of the effects implies that the physical properties of a dielectric can be controlled with the electric field of light, offering the potential for petahertz-bandwidth signal manipulation.


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