Stability of single-mode emission from a laser

It is shown that single-mode emission may be unstable in the absence of spatial and spectral "hole burning" if the distribution of the losses in the resonator is inhomogenous. An expression is obtained for the instability growth increment on the assumption that the single-pass gain is small when allowance is made for the gain dispersion. It is demonstrated that, in general, there are two pump power thresholds, i.e., single-mode emission is unstable, when the pumping rate lies in a certain range that depends on the parameters of the resonator and the medium it contains.