Typically a stimulated photon will be one of a pair with its stimulating photon. 

If the leading photon is absorbed by a particle in the ground state, will it then be re-emited by the stimulated emission caused by the second photon? 

If it causes a stimulated emission from an excited particle, will there then be a train of three photons, or will the new pair leave the excited particle excited? 

I am interested in the case where there is not a population inversion, but presumably the same rules would apply to lasers.