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Integrated photonics breakthrough enables continuous e-beam modulation

Technology News |
By Nick Flaherty

Experiments at EPFL in Switzerland, the Max Planck Institute for Biophysical Chemistry in Germany and the University of Göttingen could lead to entirely new quantum measurement schemes in electron microscopy.

Transmission electron microscope (TEM) is a well established technique for imaging molecular structures at the atomic scale by using electrons instead of light, and has revolutionized materials science and structural biology.

Researchers have successfully demonstrated extremely efficient e-beam modulation using integrated photonic microresonators. The study was led by Professor Tobias Kippenberg at EPFL and Professor Claus Ropers at the Max Planck Institute for Biophysical Chemistry and the University of Göttingen, and is published today in Nature.

The development also opens up the possibility of lower cost e-beam lithography systems.

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The two laboratories formed an unconventional collaboration, joining the usually unconnected fields of electron microscopy and integrated photonics that guide light on a chip with ultra-low low losses, and enhance optical fields using micro-ring resonators.

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 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.

The technique enables a strong modulation of the electron beam, with only a few milliwatts from a continuous wave laser. This is 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,” said Kippenberg.

“Interfacing electron microscopy with photonics has the potential to uniquely bridge atomic scale imaging with coherent spectroscopy,” said 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 work was funded by the Deutsche Forschungsgemeinschaft (DFG), Swiss National Science Foundation (SNF) and EBEAM and SEPhiM projects in Horizon 202 as well as the US Air Force Office of Scientific Research (AFOSR).

10.1038/s41586-021-04197-5; www.epfl.ch

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