Effects of saturation and self-saturation in unidirectional-wave spectroscopy of transition between levels with a total moment of $J=1$

Nonlinear absorption of a probe field in a system of degenerate levels of an atom characterized by a total moment of $J=1$ in unidirectional waves is studied analytically and numerically taking into account saturation by its own spontaneous emission (OSE). The trends in changes of the amplitude and frequency characteristics of the nonlinear resonance associated with open and closed types of transitions for different polarizations of the waves that are introduced by self-saturation are established. Specific manifestations of the effect, including those related to magnetic coherence of levels, are revealed.