Scientists in Switzerland and Germany have achieved efficient electron-beam
modulation using integrated photonics—circuits that guide light on a chip.
The experiments could lead to entirely new quantum measurement schemes in
electron microscopy.
The transmission electron microscope (TEM) can image molecular structures at
the atomic scale by using electrons instead of light, and has revolutionized
materials science and structural biology. The past decade has seen a lot of
interest in combining electron microscopy with optical excitations, trying,
for example, to control and manipulate the electron beam by light. But a
major challenge has been the rather weak interaction of propagating
electrons with photons.
In a new study, researchers have successfully demonstrated extremely
efficient electron beam modulation using integrated photonic
microresonators. The study was led by Professor Tobias J. Kippenberg at EPFL
and by Professor Claus Ropers at the Max Planck Institute for Biophysical
Chemistry and the University of Göttingen, and is published in Nature.
The two laboratories formed an unconventional collaboration, joining the
usually unconnected fields of electron microscopy and integrated photonics.
Photonic integrated circuits can guide light on a chip with ultra-low low
losses, and enhance optical fields using micro-ring resonators. In the
experiments conducted by Ropers' group, an electron beam was steered through
the optical near field of a photonic circuit, to allow the electrons to
interact with the enhanced light. The researchers then probed the
interaction by measuring the energy of electrons that had absorbed or
emitted tens to hundreds of photon energies. The photonic chips were
engineered by Kippenberg's group, built in such a way that the speed of
light in the micro-ring resonators exactly matched the speed of the
electrons, drastically increasing the electron-photon interaction.
The technique enables a strong modulation of the electron beam, with only a
few milli-Watts from a continuous wave laser—a power level generated by a
common laser pointer. The approach constitutes a dramatic simplification and
efficiency increase in the optical control of electron beams, which can be
seamlessly implemented in a regular transmission electron microscope, and
could make the scheme much more widely applicable.
"Integrated photonics circuits based on low-loss silicon nitride have made
tremendous progress and are intensively driving the progress of many
emerging technologies and fundamental science such as LiDAR,
telecommunication, and quantum computing, and now prove to be a new
ingredient for electron beam manipulation," says Kippenberg.
"Interfacing electron microscopy with photonics has the potential to
uniquely bridge atomic scale imaging with coherent spectroscopy," adds
Ropers. "For the future, we expect this to yield an unprecedented
understanding and control of microscopic optical excitations."
The researchers plan to further extend their collaboration in the direction
of new forms of quantum optics and attosecond metrology for free electrons.
The silicon nitride samples were developed in the Center of
MicroNanoTechnology (CMi) at EPFL. The experiments were conducted at the
Göttingen Ultrafast Transmission Electron Microscopy (UTEM) Lab.
Reference:
Claus Ropers et al, Integrated photonics enables continuous-beam electron
phase modulation, Nature (2021).
DOI: 10.1038/s41586-021-04197-5
Tags:
Physics