  The advanced-wave picture is "... an intuitive treatment of two-photon
correlation with the help of the concept of an effective field acting upon one
of the two detectors and formed by parametric conversion of the advanced wave
emitted by the second detector ..." [A. V. Belinskii and D. N. Klyshko, JETP
78, 259 (1994)]. This quote from Belinskii and Klyshko nicely describes the
concept of the advanced-wave picture; an intuitive tool for designing and
predicting results from coincidence-based two-photon experiments. Up to now,
the advanced-wave picture has been considered primarily for the case of an
ideal plane-wave pump beam and only for design purposes. Here we study the
advanced wave picture for a structured pump beam and in the context of
stimulated emission provoked by an auxiliary input laser beam. This suggests
stimulated parametric down-conversion as a useful experimental tool for testing
the experimental sets designed with the advanced-wave picture. We present
experimental results demonstrating the strategy of designing the experiment
with advanced-wave picture and testing with stimulated emission.
