Short pulse evolution in two-photon-absorbing media as a function of frequency and initial energy

A numerical analysis is made of the frequency dependence of the evolution of the envelopes and energy loss of short optical pulses propagating under two-photon resonance conditions. It is established that for pulses with an initial energy situated in the range $2\pi(m+1)>\theta_0>2\pi m$, there are $m$ intervals of resonance-frequency detunings within which the pulse evolution differs qualitatively. It is shown that a quasimultistage frequency dependence of the energy loss for a fixed length of medium may serve as a test for the coherence of the resonant interaction.