Asymmetry of the amplification of light in optically dense active media

An asymmetry effect in the amplification and efficiency of an optically dense amplifier is predicted theoretically and confirmed experimentally for opposite and concurrent collinear signal and pump paths. The effect is due to a difference in the losses as a result of the two-stage absorption of pump radiation in a system of luminescing centers described by a model of three energy levels. Calculations are made of various characteristics of this type of amplifier using the quasisteady-state approximation.