A theoretical investigation is made of transient energy exchange in the course of two-wave mixing in resonantly absorbing media. The optimal conditions for amplification of a weak pulse in the field of a cw pump and of a coherently propagating powerful pulse are identified and determined.
Equations describing a transient degenerate four-wave interaction in a resonant medium are derived and solved numerically. The approximation of a "following" nonlinear polarization state is used to determine the range of values of the parameters of the medium and the radiation field in which the efficiency of a transient four-wave interaction is higher than that of the steady-state process. It is found that amplification of weak radiation as a result of transient energy exchange can only be achieved in the four-wave interaction for different pump wave intensities.
A theoretical study is made of a linear, in respect of the field of lower frequency (signal), transient double resonance in a system with a shared upper level. The radiation of higher frequency (pump) is selected to be a 2π pulse which is spectrally much narrower than the contour of the Doppler scatter of the frequencies of a transition which is in resonance with this pulse. A condition is found for the appearance of a signal pulse of constant profile moving at the velocity of the pump pulse and growing exponentially in the course of its propagation into a resonant medium. It is shown that in general the energy of a signal pulse depends nonmonotonically on the energy of the pump pulse: there is an optimal value of the pump energy at which the rate of rise of the signal energy is maximal. A study is made of the efficiency of a double resonance on the detuning from a resonance in the pump and signal channels.