The 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 HeNe dc laser with the transitions 3s2 → 2p4 and 2s2 → 2p4 lasing simultaneously.