Improved inverse design method based on AVM for long-distance dielectric laser accelerators

The dielectric laser accelerator (DLA) is an innovative on-chip particle accelerator that employs a periodic dielectric structure to modulate a laser beam, generating a longitudinal accelerating field to propel particles. Leveraging the high laser-induced damage threshold of dielectric materials, DLAs can achieve significantly higher acceleration gradients compared to traditional accelerators. Current inverse design approaches for DLAs, based on the adjoint variable method (AVM), overlook the impact of changes in electron velocity, which can result in dephasing between electrons and the accelerating field over long distances. To address this limitation, we propose an improved inverse design method that incorporates electron velocity variations into the objective function, specifically tailored for long-distance acceleration structures. Using an incident electric field amplitude of 1.2 GV/m, we designed a 20 µm DLA capable of accelerating 26.6 keV electrons with an average acceleration gradient of 347 MeV/m. Our method ensures sustained electron acceleration across the entire structure, surpassing the energy gain limits imposed by the original approach. Furthermore, the optimal initial electron energy in this design closely aligns with the target value (26.6 keV), demonstrating that the dephasing issue has been effectively resolved. This advancement paves the way for more efficient and robust on-chip particle acceleration.