  We numerically and experimentally show that all photons generated by
spontaneous parametric down-conversion (SPDC) follow a transverse amplitude
similar to that of the pump. This amplitude transfer from pump to SPDC is
revealed in the Fourier image plane of the down-converted photons restricted by
an aperture. We also observe a considerable shift of the image plane from the
actual Fourier plane, when size of the aperture is gradually increased. The
shift of the Fourier image of down-converted photons affects the quality of
spatial mode-based projection in various quantum correlation experiments with
parametric down-converted photon pairs. The results may be useful in
applications of down-converted photons for quantum imaging and quantum
communication.
