PROPAGATION OF WAVES IN THE SPECTRUM OF A MULTIMODE LASER

We show that the longitudinally multimode class-B laser can behave as a chain of locally coupled oscillators, each being associated to one m ode. Propagation of waves in the laser spectrum is demonstrated theore tically and experimentally in the case of a Nd-doped fiber laser. By e xtracting the dispersion curves, we show that the group and phase velo cities always have opposite signs. This property is a direct consequen ce of the mode coupling nature (cross saturation), and does not seem t o depend on the model details.