Laser-driven particle acceleration on a chip: status and applications

Dielectric laser acceleration (DLA) of electrons in nanophotonic structures is the analog of classical radio-frequency cavity-based particle acceleration but operating in the optical regime and using microfabricated photonic devices. Boundary conditions are chosen such that a structured vacuum results ideally suited to accelerate particles with the help of oscillating electro-magnetic fields. In conventional particle accelerators, these fields lie in the RF to microwave frequency range, while in the DLA case optical fields in the form of pulsed laser beams are being employed. DLA research has recently taken two major steps. The first optical wave-guide-fed DLA chip has been demonstrated. Based on silicon-on-insulator fabrication technology, two optical waveguides, the required laser beam input coupler and the accelerator channel have been incorporated on a single chip [1]. Driven with 1.94 µm central wavelength laser pulses at a peak field strength of 335 MV/m, a peak acceleration gradient of 30.5 MeV/m was demonstrated. In another experiment, active optical transport of electrons through a record-long DLA structure was demonstrated. We have recently demonstrated the concept of alternating phase focusing for the first time at optical frequencies and inside of a nanophotonic channel [2]. In principle, this technique allows us to guide electrons through the sub-micron-wide DLA channel over arbitrarily long distances with minimal particle loss. Active beam control is crucial for any particle accelerator to confine and transport the beam while it is being accelerated. Building from these results, within this year we plan to build an integrated particle accelerator on a chip to accelerate electrons from below 100 keV to 1 MeV. We will report on the experimental progress towards this goal and give an outlook on initial applications in science, radio-biology and as a medical treatment tool. ACHIP is generously funded by the Gordon and Betty Moore Foundation. We acknowledge the contributions of all ACHIP team members. [1] Neil V. Sapra, Ki Youl Yang, Dries Vercruysse, Kenneth J. Leedle, Dylan S. Black, R. Joel England, Logan Su, Rahul Trivedi, Yu Miao, Olav Solgaard, Robert L. Byer, Jelena Vuckovic, On-chip integrated laser-driven particle accelerator, Science 367, (2020), 79 [2] Johannes Illmer, Roy Shiloh, Tomas Chlouba, Peyman Yousefi, Norbert Schönenberger, Uwe Niedermayer, Anna Mittelbach, Peter Hommelhoff, Complex electron phase space control for on-chip laser-driven particle accelerators, manuscript in preparation