High Impact of Ultrafast Physics

Light waves and their electromagnetic fields oscillate at rates on the order of a million billion times per second. In principle then, light can be employed to modulate the behavior of electrons in solid-state matter at similar rates. (Source: A. Gelin)

Physicists can now control light in both time and space with hitherto unima­gined precision. This is particularly true for the ability to generate ultra­short light pulses in the infrared and visible regions of the spectrum. Extremely high-energy laser pulses, each lasting for a few femto­seconds, have made specta­cular experiments possible, which have in turn yielded revo­lutionary insights. Above all, the growth in under­standing of the inter­action between light and electrons opens up entirely new prospects for the future of elec­tronics. Stanislav Kruchinin, Ferenc Krausz and Vladislav Yakovlev from the Labora­tory for Atto­second Physics, which is jointly run by Ludwig-Maximilians-Univer­sität (LMU) and the Max Planck Institute of Quantum Optics (MPQ) in Munich, provide now a timely overview of current research in ultra­fast solid-state physics. They describe recent break­throughs and take a look at what we can expect from the field in the coming years.

The realm of electrons is becoming ever more familiar. One reason why is that researchers have learned to produce and precisely shape ultrashort pulses of light that enable them to probe the behavior of charged particles. A single oscil­lation of the electro­magnetic field associated with such a laser pulse is sufficient to excite electrons in atoms, molecules, and condensed matter. Inter­actions between ultra­short laser pulses and electrons take place on timescales ranging from a few femto­seconds to a few hundred atto­seconds. For more than 15 years, laser pulses have been used to probe the motions of electrons in atomic gases. Meanwhile, further advances have led to methods for generating atto­second pulses which make it possible to film the behavior of electrons in real time. “We now know a good deal about what goes on in the world of electrons, and how these particles behave in response to light,” says Yakovlev. “The micro­cosmos is no longer quite as strange as it once appeared to us.”

Moreover, these unfatho­mably brief light flashes can do much more than pas­sively tracking the dynamics of electron motions. As Krausz’s team has shown, such pulses can be uti­lized to control the behavior of electrons. In 2012, the Munich researchers used highly ener­getic, ultra­short laser pulses to induce a current in a crystal and to control the direction of electron flow via the electric field of light. Light waves and their electro­magnetic fields oscil­late at rates on the order of a million billion times per second. In principle then, light can be employed to modu­late the behavior of charged particles, such as electrons, in solid-state matter at similar rates. In the near future, our growing know­ledge of electron motions optically modulated at optical fre­quencies may well lead to new develop­ments in high-speed techniques for the inves­tigation of condensed matter. Further­more, the use of light to direct electron flows may lead to a new era of opto­electronics, marked by a drastic reduction in switching times and a con­comitant increase in the perfor­mance of electronic circuits, enabling compu­tations to be carried out at optical fr­equencies.

“Ultrafast, laser-based technologies give us the chance to develop the technology of the future,” says Yakovlev. “Now, we must consider how to make the best use of our insights and expertise.” Yakovlev and his colleagues hope that the use of precisely shaped optical fields to control electron flows will usher in a new era in electronics. (Source: MPQ)

Reference: S. Kruchinin et al.: Colloquium: Strong-field phenomena in periodic systems, Rev. Mod. Phys. 90, 021002 (2018); DOI: 10.1103/RevModPhys.90.021002

Link: Laboratory for Attosecond Physics, Max Planck Institute of Quantum Optics MPQ, Munich, Germany

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