  Quantum stochastic differential equations have been used to describe the
dynamics of an atom interacting with the electromagnetic field via
absorption/emission processes. Here, by using the full quantum stochastic
Schroedinger equation proposed by Hudson and Parthasarathy fifteen years ago,
we show that such models can be generalized to include other processes into the
interaction. In the case of a two-level atom we construct a model in which the
interaction with the field is due either to absorption/emission processes
either to direct scattering processes, which simulate the interaction due to
virtual transitions to the levels which have been eliminated from the
description. To see the effects of the new terms, the total, elastic and
inelastic eloctromagnetic cross sections are studied. The new power spectrum is
compared with Mollow's results.

Quantum Physics