High Dose-Rate MeV Electron Beam from a Tightly-Focused Femtosecond IR Laser in Ambient Air

Ultrashort electron beams with femtosecond to picosecond bunch durations offer unique opportunities to explore active research areas ranging from ultrafast structural dynamics to ultra-high dose-rate radiobiological studies. It presents a straightforward method to generate relativistic electron beams in ambient air via the tight focusing of a few-cycle, mJ-class femtosecond infrared laser. It demonstrates experimentally that electrons can reach up to 1.4 MeV at a dose-rate of 0.15 Gy/s, providing enough dose rate for radiation therapy applications. 3D Particle-In-Cell simulations confirm that the acceleration mechanism is based on the relativistic ponderomotive force and show theoretical agreement with the measured electron energies and divergence. Relativistic peak intensities up to 1019 Wcm-2 are reached in ambient air due to a very low B-integral accumulation during focusing, which prevents intensity clamping. Furthermore, it discusses the scalability of this method with the continuing development of mJ-class high average power lasers, and providing a promising approach for FLASH radiation therapy. The generation of a high dose-rate (0.15 Gy/s), 1 MeV electron beam produced through pondermotive laser acceleration simply by tight focusing a mJ-class, femtosecond, 100 Hz, infrared laser in ambient air is reported. The measured beam characteristics are supported by 3D Particle-In-Cell simulations. The technique is scalable and provides a promising approach for FLASH radiation therapy.image