Propagation of a U-shaped radio pulse in a selectively amplifying medium

General relations are obtained that govern the evolution of the leading edge of a signal propagating in a selectively amplifying medium. The propagation of a pulse with a rectangular envelope, the carrier frequency of which is close to the frequency of one of the spectral amplification lines of a selective (in frequency) amplifying medium, is considered. The time dependence of the envelope of the initially rectangular signal is studied for various values of the optical thickness of the substance layer for the Gaussian and Lorentzian contours of the spectral line. It is shown that in the case of a shift of the carrier frequency of the signal relative to the center of the spectral line, the interference of the primary and amplified signal can lead to very significant oscillations of the total signal in time.