[en] The dynamics of a two-mode laser is studied in the presence of a selective saturable absorber interacting only with one of the modes. The specific nature of the system is determined by the presence of the out-of-phase relaxation oscillation, which becomes undamped when a sufficiently dense saturable absorber interacts with the weaker mode. If the absorber interacts with the stronger mode, the in-phase relaxation oscillation is excited, and the situation becomes similar to that observed in a single-mode laser. In the case of a slowly relaxing absorber, the difference of populations of its working levels can be adiabatically excluded. This procedure substantially simplifies the model and does not change its dynamic characteristics. (lasers)

[en] The dynamics of a neodymium-doped bipolarised fibre laser were investigated both theoretically and experimentally. It was found that the state of pump polarisation affects the intensity ratio of polarisation modes. The intensity fluctuation spectrum of each polarisation mode exhibits three relaxation peaks. The observed experimental features of low-frequency dynamics of the fibre laser are explained on the basis of an advanced model of a class B laser with two orthogonal elliptically polarised modes. (control of laser radiation parameters)