  Quantum states with non-Gaussian statistics generated by optical parametric
oscillators (OPO) with fluctuating parameters are studied by means of the
Kurtosis excess of the external field quadratures. The field generated is
viewed as the response of a nonlinear device to the fluctuations of laser pump
amplitude and frequency, crystal temperature and cavity detuning, in addition
to quantum noise sources. The Kurtosis excess has been evaluated perturbatively
up to the third order in the strength of the crystal nonlinear coupling factor
and the second order in the classical fluctuating parameters. Applied to the
device described in Opt. Expr. 13, 948-956 (2005) the model has given values of
the Kurtosi excess in good agreement with the measured ones.
