AbstractThe mutual influence of two laser modes corresponding to two different transitions with the same lower level is investigated by expressing the losses of each resonator as a function of the photon numbers of both laser modes. The calculations are performed in two different ways:aby using rate equations based upon the concept of constant transition probabilities independent of subsequent transitions.bin the frame of semiclassical theory of laser action.The difference between the results a) and b) displays the effect of reduced transition rates due to a perturbation of the lower level, already discussed in preceding papers [1, 2]. Numerical values are given for the case of a HeNe dc laser with the transitions 3s2→ 2p4and 2s2→ 2p4lasing simultane