  In this work I present a detailed description of the simplest nonlinear model
for an optical wavelength paramagnetic phaser, which is an acoustic analog of
the class-B lasers. Despite of its simplicity, this model gives a satisfactory
explanation of experimental data for optical-wavelength paramagnetic phasers
based on high-quality acoustic Fabry-Perot resonators. In particular, this
model was successfully used both for qualitative and quantitative
interpretation of deterministic chaotic motions observed in spin-phonon system
of a nonautonomous ruby phasers at liquid helium temperatures (see
arXiv:0704.0123v1 [nlin.CD]).
