  Applying stochastic differential equations, we study the squeezing and
statistical properties of the cavity and output modes of a degenerate
three-level laser whose cavity contains a parametric amplifier and coupled to a
squeezed vacuum reservoir. We consider the case in which the top and bottom
levels of the three-level cascade atoms injected into the cavity are coupled by
the pump mode emerging from the parametric amplifier. It turns out that the
presence of the squeezed vacuum reservoir and the parametric amplifier
contribute considerably to the mean photon number and the degree of squeezing
of the cavity and output modes. It appears that almost perfect squeezing can be
achieved at steady state and at threshold for a suitable choice of parameters.
