Possibilities of efficient frequency conversion in active media

It is shown that parametric amplification of signal waves of frequencies ω_s=ω _l± 2ω_p and ω_s=2ω_p– ω _l traveling in an inverted medium in the presence of a pump wave (frequency ω_p) has the same gain as the laser wave (ω _l) and occurs over a distance considerably greater than the linear phase-matching length. The possibility of experimental realization of such processes is considered.