Stationary emission and stability of a detuned cascade laser

The stationary emission and stability of a three-level cascade laser in which two fields of different frequencies can be simultaneously amplified is investigated under conditions of cavity detuning. Different monomode and bimode solutions are found and analysed for the effects of different pitchfork and Hopf bifurcations. At moderate cavity detunings, features different from those observed in other classes of lasers are found, such as for instance a decrease in the instability threshold when detuning is introduced. Particular attention is paid to the case of resonance of the two-photon transition, which allows us to study the continuous evolution, when detuning is increased, of a resonant cascade laser towards a pure two-photon laser. In particular, this establishes the origin of some features which are characteristic of two-photon lasers.