  An effective scheme of synchronized laser-triggered ion acceleration and the
corresponding theoretical model are proposed for a slow light pulse of
relativistic intensity, which penetrates into a near-critical-density plasma,
strongly slows, and then increases its group velocity during propagation within
a target. The 3D PIC simulations confirm this concept for proton acceleration
by a femtosecond petawatt-class laser pulse experiencing relativistic
self-focusing, quantify the characteristics of the generated protons, and
demonstrate a significant increase of their energy compared with the proton
energy generated from optimized ultrathin solid dense foils.
