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| Light pulses emit electrons bursts from a metallic nanotip that last merely 53 attoseconds. Credit: Eleftherios Goulielmakis, University of Rostock |
By using ultrafast laser flashes, scientists at the University of Rostock in
collaboration with researchers of the Max Planck Institute for Solid State
Research in Stuttgart have generated and measured the shortest electron
pulse to date. The electron pulse was created by using lasers to remove
electrons from a tiny metal tip and lasted only 53 attoseconds, that is, 53
billionths of a billionth of a second. The event has set a new speed record
in man-made control of electric currents in solid materials.
The research opens new avenues for advancing the performance of electronics
and information technologies, as well as developing new scientific
methodologies for visualizing phenomena in the microcosm at ultimate speeds.
Ever wondered what makes your computer and your other electronic gadgets
slow or fast in their performance? It is the time it takes electrons, some
of the tiniest particles of our microcosm, to stream out from minute leads
inside the transistors of electronic microchips and to form pulses. Methods
to speed up this process are central for advancing electronics and their
applications to ultimate performance limits. But what is the shortest
possible streaming time of electrons from a tiny metal lead in an electronic
circuit?
By using extremely short laser flashes, a team of researchers led by
Professor Eleftherios Goulielmakis, head of the group Extreme Photonics of
the institute for Physics at the University of Rostock, and collaborators at
the Max Planck Institute of Solid State Research in Stuttgart used
state-of-the art laser pulses to eject electrons from a tungsten nanotip to
generate the shortest electron burst to date. This work is published in
Nature.
Whereas it has long been known that light can release electrons from
metals—Einstein was the first to explain how—the process is extremely hard
to manipulate. The electric field of light changes its direction about a
million billion times per second making it challenging to control the way it
rips off electrons from the surface of metals.
To overcome this challenge, the Rostock scientists and their co-workers used
a modern technology that had been previously developed by their group—light
field synthesis—which allowed them to shorten a light flash to less than a
full swing of its own field. In turn, they used these flashes to illuminate
the tip of a tungsten needle to knock electrons free into vacuum.
"Using light pulses that comprise merely a single cycle of its field, it is
now possible to give electrons a precisely controlled kick to set them free
from the tungsten tip within a very short time interval," explains
Eleftherios Goulielmakis, head of the research group.
But the challenge could not be overcome unless the scientists also found a
way to measure the brevity of these electron bursts. To deal with this
hurdle, the team developed a new type of camera that can take snapshots of
the electrons during the short time the laser is pushing them out from the
nanotip and into the vacuum.
"The trick was to use a second, very weak, light flash" said Dr. Hee-Yong
Kim, the leading author of the new study. "This second laser flash can
gently perturb the energy of the electron burst to find out how it looks
like in time. It is like the game 'What's in the box?' where players try to
identify an object without looking at it but just by turning it around to
feel its shape with their hands."
But how could this technology be used in electronics? "As technology
advances rapidly, it is reasonable to expect the development of microscopic
electronic circuits in which electrons travel in a vacuum space among
closely packed leads to prevent obstacles that slow them down," says
Goulielmakis. "Using light to eject electrons and drive them among these
leads could speed up future electronics by several thousand times of today's
performance."
But the researchers believe that their newly developed methodology will be
used directly for scientific purposes. "Ejecting electrons from a metal
within a fraction of a light's field cycle dramatically simplifies the
experiments and allows us to use advanced theoretical methods to understand
the emission of electrons in ways that were not previously possible," says
Professor Thomas Fennel, a coauthor in the new publication.
"Since our electron bursts provide excellent resolution for taking snapshots
of electronic and atomic motions in materials, we plan to use them to
acquire a deep understanding of complex materials to facilitate their
applications in technology," Goulielmakis says.
Reference:
H. Y. Kim et al, Attosecond field emission, Nature (2023).
DOI: 10.1038/s41586-022-05577-1
Tags:
Physics