Multimode instability in inhomogeneously broadened class-B ring lasers:: Beyond the uniform-field limit -: art. no. 053805

The multimode emission threshold of class-B ring lasers is analytically investigated taking into account the localized nature of the cavity losses and the inhomogeneous broadening of the amplifying medium. This analysis finds a relevant application to erbium-doped fiber lasers (EDFL's). The main conclusion is that the predictions of the simplest models are deeply modified both quantitatively and qualitatively. Thus, any attempt to interpret multimode emission in EDFL's must incorporate the two considered factors. Two main results are: (i) While in homogeneously broadened lasers instabilities are inhibited for values of the mirrors' reflectivity R<0.54ca, this limitation disappears as soon as the inhomogeneous width exceeds 0.9 times the homogeneous width: and (ii) the band of unstable modes is reduced as cavity losses increase.