Flying-focus laser beats dephasing limit in plasma electron acceleration, Nature Physics study finds

Researchers accelerated electrons to more than twice the energy predicted by the traditional dephasing limit for laser-plasma accelerators over the same distance, using a specially engineered "flying focus" laser pulse, phys.org reported of a Nature Physics study. Laser-plasma accelerators drive a charge wave through plasma with an ultrashort laser pulse, aiming for high particle energies over centimeters rather than kilometers. Dephasing occurs when ultra-relativistic electrons outrun the slightly slower plasma wave set by the laser's group velocity, ending acceleration early. First author Dr. Charlie Arrowsmith of the University of Rochester's Laboratory for Laser Energetics said dephasing ends acceleration when electrons catch up with the driving laser pulse. The team used dephasingless laser wakefield acceleration, steering the pulse's peak intensity forward at a chosen speed with specialized optics including an axiparabola mirror fabricated in-house at LLE. In a hydrogen-argon mixture and a narrow plasma density window of roughly 4.5 to 5.4 × 10¹⁸ cm⁻³, electrons reached up to 396 ± 14 MeV, more than twice the 185 MeV dephasing-limited energy calculated for the same conditions with conventional laser wakefield acceleration. The paper suggests reaching 100 GeV would require an accelerator length under a meter, about a 20-fold reduction versus a traditional single-stage laser-plasma design at that energy. DOI: 10.1038/s41567-026-03352-x.