A Switch for Light Wave Electronics

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Light waves might be able to drive future transistors. The electromagnetic waves of light oscillate approximately one million times in a billionth of a second, hence at petahertz frequencies. In principle future electronics could reach this speed and become 100.000 times faster than current digital electronics.

A team of the Laboratory for Attosecond Physics (LAP) at the Max-Planck Institute of Quantum Optics (MPQ), the Ludwig-Maximilians University Munich (LMU) and the Technical University of Munich (TUM) in collaboration with theorists from the University of Tsukuba have optimized the interaction of light and glass in a way that facilitates its possible future usage for light wave driven electronics (Nature, "Attosecond nonlinear polarization and light-matter energy transfer in solids").

Electron movements form the basis of electronics as they enable storage, processing and transfer of information. State-of-the-art electronic circuits have reached maximum clock rates of several billion switching cycles per second, limited by the heat accumulated in the process of switching power on and off.

The electric field of light changes its direction a trillion times per second and is able to move electrons in solids at this speed. Thus light waves could form the basis for future electronic switching once the induced electron motion and its influence on heat accumulation is precisely understood.

Physicists from the Laboratory for Attosecond Physics have already found out that it is possible to manipulate the electronic properties of matter at optical frequencies. In a follow-up experiment the researchers, in a manner similar to their previous approach, shot extremely strong, femtosecond-laser pulses (one femtosecond is a millionth of a billionth of a second) onto silicon dioxide glass.

A single oscillation

The light pulse comprises only a single strong oscillation cycle of the field, hence the electrons are moved left and right only once. The full temporal characterization of the light field after transmission through the thin glass plate now, for the first time, provides direct insight into the attosecond electron dynamics, induced by the light pulse in the solid.

This measurement technique reveals that electrons react with a delay of only some ten attoseconds (one attosecond is a billionth of a billionth of a second) to the incoming light. This time delay in the reaction determines the energy transferred between light and matter.

Since it is now possible to measure this energy exchange within one light cycle, the parameters of the light-matter interaction can be understood and optimized to reach out for the ultimate speed in signal processing. The more reversible the exchange and the smaller the residual energy left in the medium after the light pulse has passed, the more suitable the interaction for future light field-driven electronics.

Cool relationship

To understand the observed phenomena and identify the best set of experimental parameters to that end, the experiments were backed up by a novel simulation method based on first principles developed at the Center for Computational Sciences at University of Tsukuba. The theorists there used the K computer, currently the fourth fastest supercomputer in the world, to compute electron movement inside solids with unprecedented accuracy.

Finally, the researchers succeeded in optimizing the energy consumption by adapting the amplitude of the light field. At certain field strengths energy is transferred from the field to the solid during the first half of the pulse cycle and is almost completely emitted back in the second half of the light.

These findings verify that a potential switching medium for future light-driven electronics need not overheat. Thus the ‘cool relationship’ between glass and light might provide an opportunity for dramatically accelerating electronic signal and data processing, up to the ultimate limit.