'Whispering gallery' effect controls electron beams with light
Research succeeds in coupling free electrons to optical resonators

Date:
June 5, 2020
Source:
University of Go"ttingen
Summary:
When you speak softly in one of the galleries of St Paul's
cathedral, the sound runs around the dome and visitors anywhere on
its circumference can hear it. This striking phenomenon has been
termed the 'whispering gallery' effect, and one variant is where
a wave travels nearly perfectly around a structure. Researchers
have now harnessed the effect to control the beam of an electron
microscope by light.



FULL STORY ==========================================================================
When you speak softly in one of the galleries of St Paul's cathedral,
the sound runs so easily around the dome that visitors anywhere on its circumference can hear it. This striking phenomenon has been termed the 'whispering gallery' effect, and variants of it appear in many scenarios
where a wave can travel nearly perfectly around a structure. Researchers
from the University of Go"ttingen have now harnessed the effect to
control the beam of an electron microscope by light. The results were
published in Nature.


==========================================================================
In their experiments, the team of Dr Ofer Kfir and Professor Claus Ropers illuminated small spheres of glass with a laser, trapping light in a
so-called 'optical whispering-gallery mode'. Similar to the acoustics
example, the light wave travels around in these spheres almost without
damping. In their electron microscope, the researchers then passed a beam
of electrons near the edge of the sphere. By measuring the distribution
of electron velocities, they discovered that the electrons and the light
field had exchanged large amounts of energy.

According to first author Kfir, the strength of the interaction arises
from two contributions: "First, the whispering gallery effect allows us
to store light and use the time to build up a stronger wave. Second,
the electrons run at the same velocity as the light wave on the glass
sphere." He explains: "Think of a surfer that matches the speed of
the wave in order to best use its energy." In the study, the physicists observed that individual electrons had picked up or given away the energy
of hundreds of photons, the elementary particles of the light field.

Besides the fundamental interest in this phenomenon, the researchers
believe that their findings have considerable future relevance. "We
investigate ways in which light can add functionality to electron
microscopy," says Ropers from the Faculty of Physics, the leader of
the team and Director at the Max Planck Institute for Biophysical
Chemistry. "We can now use light to steer the beam of electrons in
space and time. Enhancing the coupling of free electrons and photons
may eventually lead to entirely new quantum technologies for nanoscale
sensing and microscopy. We are confident that the present work is an
important step in this direction."

========================================================================== Story Source: Materials provided by University_of_Go"ttingen. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Ofer Kfir, Hugo Lourenc,o-Martins, Gero Storeck, Murat Sivis,
Tyler R.

Harvey, Tobias J. Kippenberg, Armin Feist, Claus Ropers. Controlling
free electrons with optical whispering-gallery modes. Nature,
2020; 582 (7810): 46 DOI: 10.1038/s41586-020-2320-y ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200605105357.htm

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