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 inv estigated 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 con clusion is that the predictions of the simplest models are deeply modified both quantitatively and qualitatively. Thus, any attempt to interpret multi mode emission in EDFL's must incorporate the two considered factors. Two ma in results are: (i) While in homogeneously broadened lasers instabilities a re inhibited for values of the mirrors' reflectivity R<0.54ca, this limitat ion disappears as soon as the inhomogeneous width exceeds 0.9 times the hom ogeneous width: and (ii) the band of unstable modes is reduced as cavity lo sses increase.