Study of the effect of pump focusing on the performance of ghost imaging and ghost diffraction, based on spontaneous parametric downconversion

We study the effects of ghost imaging (GI) and ghost diffraction (GD), based on spontaneous parametric downconversion (SPDC) photon-pair sources. In particular, we focus on the effect of pump focusing in the SPDC process, on GI and GD. Our theory presented in this paper includes the cases of frequency-degenerate and frequency non-degenerate SPDC. We show analytically, and confirm through numerical simulations, that pump focusing degrades the performance of GI and GD, and for a sufficient focusing strength can altogether suppress these effects.