  In this paper we consider an alternative formulation of a class of stochastic
wave and master equations with scalar noise that are used in quantum optics for
modelling open systems and continuously monitored systems. The reformulation is
obtained by applying J.M.C. Clark's pathwise reformulation technique from the
theory of classical nonlinear filtering. The pathwise versions of the
stochastic wave and master equations are defined for all driving paths and
depend continuously on them. In the case of white noise equations, we derive
analogs of Clark's robust approximations. The results in this paper may be
useful for implementing filters for the continuous monitoring and measurement
feedback control of quantum systems, and for developing new types of numerical
methods for unravelling master equations. The main ideas are illustrated by an
example.
