  Bloch equations for the atomic population and the polarization/coherence and
the equation of motion for the photon number in a laser are solved in steady
state as a function of the pump rate. Two level atom and two modes of three
levels atom are investigated. Close to threshold the usual linear dependence of
the intensity on the pump rate in found for all cases. However, far above
threshold strongly nonlinear dependence is encountered. In the cases for which
the pump connects the lower lasing state to one of the excited states the
character of the non-linearity differs crucially from the cases when the pump
in not related directly to the lower lasing state. Non-monotonic dependence of
laser intensity upon the pump rate is predicted. Detailed discussion of the
nonlinear behavior is presented, including saturation and depletion effects.
