Light sail boosted by instantaneous radiation pressure

Light sail acceleration by ultrashort, superintense laser pulses is presently investigated as an approach to compact accelerators of matter. The usual light sail equation assumes a cycle-averaged light pressure, which becomes questionable for ultrashort pulse drivers or in the highly relativistic regime. Here, we remove such assumption and compute solutions of the light sail equations which show oscillations of the sail acceleration. The dependence of the final sail velocity on the temporal profile of extremely short pulses is discussed.