Superradiant Amplification of an Ultrashort Laser Pulse in a Plasma by a Counterpropagating Pump

An initially short ( $<1/{\ensuremath{\omega}}_{p}$) laser pulse can be superradiantly amplified by a counterpropagating long low-intensity pump while remaining ultrashort. This superradiant amplification occurs if the frequency of the pulse is lower than that of the pump, and the initial pulse intensity is sufficiently high. Numerical simulations indicate that the short pulse can be amplified to an intensity hundreds of times the pump intensity, with the pump depletion as high as $40%$. This implies that the long pump is efficiently time compressed without frequency chirping and pulse stretching, making the superradiant amplification an interesting alternative to chirped-pulse amplification.