‘Whispering Gallery’ Effect Allows Light to Be Stored and Controls Electron Beams

Electrons, Light and a Transparent Silica Sphere

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Artist’s view of specific electrons connecting with an optical whispering gallery mode as it circles around a silica sphere. The matching in between the speeds of the electron and the light-wave it is riding modifications the quantum state of the electron, showed as a larger halo. Credit: Dr. Murat Sivis

Research group led by the University of Göttingen is successful in coupling totally free electrons to optical resonators.

When you speak gently in among the galleries of St Paul’s cathedral, the sound runs so quickly around the dome that visitors anywhere on its area can hear it. This striking phenomenon has actually been called the ‘whispering gallery’ result, and variations of it appear in lots of situations where a wave can take a trip almost completely around a structure. Researchers from the University of Göttingen have actually now utilized the result to manage the beam of an electron microscopic lense by light. The outcomes were released in Nature.

In their experiments, the group of Dr. Ofer Kfir and Professor Claus Ropers lit up little spheres of glass with a laser, trapping light in a so-called ‘optical whispering-gallery mode.’ Similar to the acoustics example, the light wave circumnavigates in these spheres nearly without damping. In their electron microscopic lense, the scientists then passed a beam of electrons near the edge of the sphere. By determining the circulation of electron speeds, they found that the electrons and the light field had actually exchanged big quantities of energy.

According to very first author Kfir, the strength of the interaction occurs from 2 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 discusses: “Think of a surfer that matches the speed of the wave in order to best use its energy.” In the research study, the physicists observed that specific electrons had actually gotten or handed out the energy of numerous photons, the primary particles of the light field.

Besides the essential interest in this phenomenon, the scientists think that their findings have significant future importance. “We investigate ways in which light can add functionality to electron microscopy,” states Ropers from the Faculty of Physics, the leader of the group 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.”

Reference: “Controlling free electrons with optical whispering-gallery modes” by Ofer Kfir, Hugo Lourenço-Martins, Gero Storeck, Murat Sivis, Tyler R. Harvey, Tobias J. Kippenberg, Armin Feist and Claus Ropers, 3 June 2020, Nature.
DOI: 10.1038/s41586-020-2320-y

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