Periodic Reporting for period 4 - AccelOnChip (Attosecond physics, free electron quantum optics, photon generation and radiation biology with the accelerator on a photonic chip)
Reporting period: 2025-04-01 to 2025-09-30
In AccelOnChip, we focus on nanophotonics-based control of electrons. By using nanophotonic structures to generate optical nearfield forces, we aim to achieve a new level of control. Our goals are twofold: building a particle accelerator on a nanophotonic chip and reaching new regimes of quantum control. We made major progress in both areas, demonstrating complex optical phase-space control of electrons (Nature 2021) and realizing the accelerator-on-a-chip concept (Nature 2023).
The project also advanced related topics, including diamond as a nanophotonic material and improved laser illumination schemes. On the quantum side of electron–light coupling, we showed that key effects can be observed even in a standard scanning electron microscope (Phys. Rev. Lett. 2022), avoiding the need for complex transmission electron microscopes. We introduced inverse photonic design to the field, enabling a high-efficiency electron–light coupling structure. In collaboration with Technion, we demonstrated that electron spectra can reveal the quantum statistics of light (Science 2021): coherent laser light and thermal light produce distinctly different spectra, even when average power and wavelength are identical. We also explored new on-chip schemes for light generation by electrons.
Our ultrafast studies of electron dynamics at needle tips reached new precision. Together with theory partners in Rostock, we measured electron emission durations with 30-attosecond precision (Nature 2023) and identified a new optical nearfield effect leading to strong-field sensitivity (Nature Physics 2025). With MPL/FAU collaborators, we further showed that quantum light can imprint its photon counting statistics onto emitted electrons (Nature Physics 2024) and can even strongly drive electron emission at needle tips (Nature Physics 2025).
The project also advanced related topics, including diamond as a nanophotonic material and improved laser illumination schemes. On the quantum side of electron–light coupling, we showed that key effects can be observed even in a standard scanning electron microscope (Phys. Rev. Lett. 2022), avoiding the need for complex transmission electron microscopes. We introduced inverse photonic design to the field, enabling a high-efficiency electron–light coupling structure. In collaboration with Technion, we demonstrated that electron spectra can reveal the quantum statistics of light (Science 2021): coherent laser light and thermal light produce distinctly different spectra, even when average power and wavelength are identical. We also explored new on-chip schemes for light generation by electrons.
Our ultrafast studies of electron dynamics at needle tips reached new precision. Together with theory partners in Rostock, we measured electron emission durations with 30-attosecond precision (Nature 2023) and identified a new optical nearfield effect leading to strong-field sensitivity (Nature Physics 2025). With MPL/FAU collaborators, we further showed that quantum light can imprint its photon counting statistics onto emitted electrons (Nature Physics 2024) and can even strongly drive electron emission at needle tips (Nature Physics 2025).
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.
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.
Before AccelOnChip, a compact accelerator—let alone one on a chip—did not exist. Our demonstration of an accelerator on a chip is therefore a scientific breakthrough with significant socio-economic potential. We envision chip-scale particle accelerators integrated into future surgical tools, enabling applications such as proximity tumor treatment. Even before full miniaturization to pen-tip size, more compact accelerators could allow smaller, more affordable electron and possibly X-ray sources, making radiation therapy cheaper and more accessible.
We also see strong prospects in quantum light–electron coupling. This could enable new forms of electron microscopy capable of imaging coherence—central to quantum technology but currently difficult to measure with high spatial resolution. In addition, our work on novel light-generation schemes addresses challenges tackled today by billion-euro facilities such as European XFEL, SwissFEL, LCLS, and SACLA. Developing new approaches may ultimately lead to compact light sources suitable for university labs or small companies.
Beyond the scientific achievements, we are in the process of founding a company to commercialize accelerator-on-a-chip technology. Dissemination has been highly successful, with broad media coverage. For example, our mini-accelerator was featured on SciShow, a YouTube channel with over 8 million subscribers (“The World’s Smallest Particle Accelerator Doesn’t Do Anything”).
We also see strong prospects in quantum light–electron coupling. This could enable new forms of electron microscopy capable of imaging coherence—central to quantum technology but currently difficult to measure with high spatial resolution. In addition, our work on novel light-generation schemes addresses challenges tackled today by billion-euro facilities such as European XFEL, SwissFEL, LCLS, and SACLA. Developing new approaches may ultimately lead to compact light sources suitable for university labs or small companies.
Beyond the scientific achievements, we are in the process of founding a company to commercialize accelerator-on-a-chip technology. Dissemination has been highly successful, with broad media coverage. For example, our mini-accelerator was featured on SciShow, a YouTube channel with over 8 million subscribers (“The World’s Smallest Particle Accelerator Doesn’t Do Anything”).