AccelOnChip is about merging nanophotonics with free electron beams. To achieve this, we translated particle acceleration concepts from the microwave RF domain to the optical domain. The electromagnetic frequencies increase by roughly a factor of 10,000, while the wavelengths decrease accordingly. Since accelerator dimensions scale with the driving wavelength, we had to turn to nanofabrication to build the structures. Cleanroom technologies such as electron beam lithography and plasma etching—standard in electronics and photonics—were now applied to particle accelerators. Our work therefore centered on designing and fabricating nanostructures in the cleanroom.
We used the cleanroom at the Max Planck Institute for the Science of Light in Erlangen, with outstanding support from the engineers and technicians (many thanks to the team around OL, IH and FG). After fabrication, we tested the structures in our optics lab. Using modified electron microscopes as electron sources, we injected pulsed electron beams into the structures and overlapped them with intense pulsed laser light. With home-built spectrometers, we measured the electron energy and confirmed that the structures performed as designed.
For joint experiments with our colleagues at the Technion in Israel, we shipped a high-efficiency electron–light coupling structure tailored to their electron energies. The structures performed so well that, using their existing setup, they immediately observed differences in electron behavior under two types of light.
For the needle tip experiments, we used ultrahigh vacuum chambers to hold the needles. By focusing laser or quantum light onto them, we measured electron energy spectra and, often with demanding quantum-mechanical simulations, reconstructed what occurred at the needle tip on attosecond timescales.
Together with our quantum light partners at MPL/FAU, we built a new ultrahigh vacuum chamber with a custom electron spectrometer to study electron dynamics driven by quantum light. The setup was compact enough to transport to their lab, where the quantum light was generated.
We also developed light-generation structures. Electron beams, either in-house or at PSI, were focused into cleanroom-fabricated devices. Using optical spectrometers, we demonstrated that these structures can generate light as intended.
The project produced extensive scientific output, published in leading journals. Team members presented the results worldwide, delivering around 200 talks. Although this was fundamental research, we filed several patents and are preparing to spin out a company. ERC funding was crucial in making this possible. Beyond the scientific impact—difficult to measure in monetary terms—we hope the project will lead to new mini-accelerator-based instruments with tangible economic benefits, and perhaps even clinical impact. As with most deep-tech ventures, this will take several more years, which we approach with great excitement. Thank you, ERC, for enabling us to lay these foundations.
