  Spin noise spectroscopy (SNS) is a new method for studying magnetic resonance
and spin dynamics based on measuring the Faraday rotation noise. In strong
contrast with methods of nonlinear optics, the spectroscopy of spin noise is
considered to be essentially nonperturbative. Presently, however, it became
clear that the SNS, as an optical technique, demonstrates properties lying far
beyond the bounds of conventional linear optics. Specifically, the SNS shows
dependence of the signal on the light power density, makes it possible to
penetrate inside an inhomogeneously broadened absorption band and to determine
its homogeneous width, allows one to realize an effective pump-probe
spectroscopy without any optical nonlinearity, etc. This may seem especially
puzzling when taken into account that SNS can be considered just as a version
of Raman spectroscopy, which is known to be deprived of such abilities. In this
paper, we clarify this apparent inconsistency.
