  The relative intensity noise (RIN) of a solid state whispering-gallery-mode
class-B laser is studied both theoretically and experimentally under different
pumping regimes. In particular, we show that harmonics of the spiking frequency
are observed in the RIN spectrum. A rate equation model including Langevin
forces and the nonlinear coupling between inverted ion and photon number
fluctuations has been developed to reproduce the experimental results and to
extract relevant physical parameters from the fitting of the RIN spectrum.
