Coherent imaging with pseudo-thermal incoherent light

We investigate experimentally fundamental properties of coherent ghost imaging using spatially incoherent beams generated from a pseudo-thermal source. A complementarity between the coherence of the beams and the correlation between them is demonstrated by showing a complementarity between ghost diffraction and ordinary diffraction patterns. In order for the ghost imaging scheme to work it is therefore crucial to have incoherent beams. The visibility of the information is shown for the ghost image to become better as the object size relative to the speckle size is decreased, and therefore a remarkable tradeoff between resolution and visibility exists. The experimental conclusions are backed up by both theory and numerical simulations. 1. Historical overview and introduction A decade has passed since the first experimental observation of unusual interference fringes in the coincidence counts of photon pairs [1, 2]. Signal and idler photons produced by parametric down-conversion (PDC) were spatially separated and in the signal photon arm a double slit was inserted. While no first order interference patter