Speaker
Description
Dielectric laser acceleration is a concept where engineered nanophotonic structures, along with femtosecond laser pulses, are used to couple photon energy to free electrons passing in close proximity to them [1]. A viable and rather direct application is electron acceleration on a chip, which has recently been shown to breach the 30 keV limit of standard scanning electron microscopes with sophisticated phase-space acrobatics [2–4]. The nanostructure is composed of potentially thousands of fundamental acceleration sections, each of which with several degrees of freedom, and perfect synchronism must be kept throughout its length for efficient coupling. To reach even higher electron energies and – importantly – a larger number of accelerated electrons, the analytical models must be replaced or in the least augmented by a full-scale optimization of the tremendous number of degrees of freedom.
To achieve this, we extended the concept of the well-known adjoint method of inverse-design [5–7] which enables us to optimize an arbitrary number of parameters using only two physical simulations per iteration. This is the only feasible algorithm for such a challenging and computationally-intense calculation. Since the algorithm is physics-guided, we had to develop it anew to deal with non-periodic and extremely long nanophotonic structures.
In this contribution, I will feature our results on electron acceleration. However, the adapted algorithm is quite versatile: we expect to use it not only for achieving record-high electron energies and currents on a chip, but also for designing nanostructures that shape the electron's spectrum, maximize electron-photon coupling, temporally-engineer electron bunches, and generally provide complete, complex control of electron pulses with light.
[1] R. Shiloh et al., Miniature light-driven nanophotonic electron acceleration and control, Advances in Optics and Photonics 14, 862 (2022).
[2] R. Shiloh, J. Illmer, T. Chlouba, P. Yousefi, N. Schönenberger, U. Niedermayer, A. Mittelbach, and P. Hommelhoff, Electron phase space control in photonic chip-based particle acceleration, Nature 597, 498 (2021).
[3] T. Chlouba, R. Shiloh, S. Kraus, L. Brückner, J. Litzel, and P. Hommelhoff, Coherent nanophotonic electron accelerator, Nature 622, 476 (2023).
[4] P. Broaddus, T. Egenolf, D. S. Black, M. Murillo, C. Woodahl, Y. Miao, U. Niedermayer, R. L. Byer, K. J. Leedle, and O. Solgaard, Subrelativistic Alternating Phase Focusing Dielectric Laser Accelerators, Phys. Rev. Lett. 132, 085001 (2024).
[5] O. D. Miller, Photonic Design: From Fundamental Solar Cell Physics to Computational Inverse Design, arXiv:1308.0212.
[6] T. Hughes, G. Veronis, K. P. Wootton, R. J. England, and S. Fan, Method for computationally efficient design of dielectric laser accelerator structures, Optics Express 25, 15414 (2017).
[7] N. V. Sapra et al., On-chip integrated laser-driven particle accelerator, Science 367, 79 (2020).