Optically tunable proton acceleration with a controlled prepulse in ultrashort intense laser double-foil target interaction

Competition and transition of the dominated mechanisms for proton acceleration were investigated in experiments by optically tuning the preplasma density profile using an additional femtosecond pre-ablation laser beam. Two groups of proton beams with angular separation were measured along the laser propagation axis and target normal direction from a vacuum-gapped double-foil target. A transition of proton acceleration from a target normal sheath acceleration regime to relativistically induced transparency (RIT) domination was observed when increasing the prepulse intensity. Two-dimensional particle-in-cell simulations qualitatively verify the experimental observations that a proton component along the laser axis is mainly generated by the RIT induced breakout afterburner from the tailored pre-expanded ultrathin front-layer foil with spatial-intensity distribution improvement by the second-layer foil. Our method can be popularized in manipulating the laser-driven proton acceleration and beam spatial quality for wide applications.

Automated summary

The competition and transition of dominant mechanisms for proton acceleration were investigated experimentally by tuning the preplasma density profile using an additional femtosecond pre-ablation laser beam. A transition from target normal sheath acceleration to relativistically induced transparency (RIT) domination was observed with increasing prepulse intensity. The experimental observations were qualitatively verified by two-dimensional particle-in-cell simulations, which showed that the proton component along the laser axis is mainly generated by RIT-induced breakout afterburner from a tailored pre-expanded ultrathin front-layer foil.