Compression of parametrically amplified pulses using ultrashort high-intensity adiabatic pumping

The problem of transient four-wave parametric interaction in a two-level medium is solved taking into account the group delay without assuming a weak exciting field. It is found that a high-power narrow peak whose duration $\tau_s$ is considerably shorter than the pump duration $\tau_p$ is observed against the background of a slowly varying envelope of the weak signal during its amplification process. In the case of a high pump intensity ($|\Omega_m|\gg\tau^{-1}_p$) the lowest possible value of $\tau_s$ that can be achieved for a suitable angle of incidence and input signal frequency is governed by $|\tau_p/\Omega_m|^{1/2}$, where $\Omega_m$ is the peak Stark shift of the resonance frequency.