PHASE DYNAMICS IN A SINGLE-MODE CLASS-B LASER

We study the phase dynamics of the electric field in the four-level model for the CO2 laser with modulated losses. We show that in the temporal evolution of the laser phase there are no phase jumps and phase plateaus are almost inexistent. The laser phase on the average increases or decreases according to the sign of the detuning. The onset of inestabilities as the detuning changes is discussed. We find two properties of the laser phase which are invariant with respect to the detuning Delta and the reference frequency Omega and as well on the initial conditions and the choice of the Poincare section. These properties show that periodic modulation of the losses induces an effective shift in the frequency of the laser field. Qualitatively similar results are obtained for the laser phase in the two-level model.