In the case of stimulated emission we always see that one photon goes into the gain medium and two photons come out. How can this conserve energy?
I believe the key point here is that the electron is already excited. So yes, a photon enters and two leave, but the electron goes from an excited state to a lower energy level.
In a way, you could say that in a photon and an excited electron changes to 2 photons and an electron with lower energy than before.
Hence, conservation of energy!