Theoretical and experimental presentations are given of a drastic suppression, during the interval of the excitation pulse, of forward-directed optically pumped stimulated emission from a two-photon resonantly excited state to a lower state which is also coupled to the ground state. The effect is caused by a self-induced interference from the difference-frequency mixing field that is generated during the time that the excitation fields are present. Several other implications of this effect are given and some puzzling observations in other studies are noted and clarified.