Mechanism behind steeper intensity scaling of TNSA ion energies with vortex beams

Determine the physical mechanism responsible for the steeper intensity scaling of maximum proton energy observed in target normal sheath acceleration (TNSA) experiments driven by vortex (Laguerre–Gaussian) laser beams compared to Gaussian focal spots, which indicates stronger coupling to laser intensity and currently lacks a theoretical explanation.

Background

Experiments at PHELIX and other facilities have compared ion acceleration driven by vortex beams versus conventional Gaussian beams in the TNSA regime. Measurements show that shots using vortex beams exhibit a significantly steeper power-law scaling of maximum proton energy with laser intensity, implying stronger coupling.

Despite consistent observations in multiple campaigns, the authors note that the dramatic improvement in scaling remains unexplained, highlighting a gap in theory regarding how the vortex beam’s structured intensity and phase (or associated OAM effects) enhance energy coupling in TNSA.