Transition Radiation Field Enhanced Laser Proton Acceleration Employing Near-Critical-Density Foam

High-efficiency energy coupling of protons from laser-induced accelerating fields is complex, hybrid acceleration mechanisms that combine multiple field contributions prove critical for optimizing proton energy. Here, we report a laser proton acceleration scheme in which proton energy can be enhanced by a transition radiation field (TRF) built by high-energy and large-charged electron bunches.

Using near-critical-density plasmas, we experimentally produce electron beams with charges up to ~30 nC (>13 MeV). As these electrons exit the target, they emit intense TRF with energy up to 0.6 J in 0.1-15 THz range, corresponding to an acceleration field of 1012–13 V m–1. When superposed with the charge-separation field (CSF), proton cut-off energy is boosted by more than a factor of two, reaching 90 MeV.