High-stability proton beams accelerated in p-polarized interactions with converging liquid jet targets

Laser-driven ion sources exhibit peak energies exceeding 100 MeV and fluxes greater than 10¹¹ particles/MeV/sr, making them compelling alternatives to conventional accelerators for applications in medicine, materials science, and fundamental physics. To realize the full potential of these sources, they must stably deliver high ion beam fluxes and energies at repetition rates at the Hz scale or beyond. Optimization of laser parameters such as the polarization and pulse shape is crucial to producing high-quality ion beams. Advanced targets, such as converging liquid sheet jets, are necessary for sustained high repetition rate ion beam generation. These targets can also enable detailed mapping of the phase space of advanced ion acceleration mechanisms beyond target normal sheath acceleration.

Here, we present results from a recent LaserNetUS experiment using the ALEPH laser at Colorado State University (400 nm, 5 J, 50 fs, 0.5 Hz). We performed the first study operating 2ω ALEPH with p-polarization on target, producing proton beams with cutoff energies up to 10 MeV. This more than doubled the maximum energy obtained in our previous experiments using s-polarized pulses. These beams also exhibited remarkable flux stability, with a relative standard deviation of 10% or less across much of the energy spectrum. We will additionally discuss preliminary experiments exploring shaping of the target density profile using pre-expansion of the liquid sheet before the arrival of the main pulse.