By means of optical phase shift measurements at low and high excitation levels, spontaneous and stimulated carrier lifetimes are determined (77°K) as a function of photon energy on nitrogen‐doped and nitrogen‐freen‐type GaAs1−xPx. Spontaneous lifetime data near laser threshold on N‐free samples show the effect of stimulated emission and intraband adjustment of electrons during sample fluorescence. Above threshold the lifetime drops sharply in the vicinity (energy or wavelength) of the sample peak laser output. Nitrogen‐doped samples show, in addition, the effect of electron transfer from the conduction band to the NN‐pair states, supporting in the process laser operation on the nitrogen states.