Fourth-order image formation by spontaneous parametric down-conversion: The effect of anisotropy

We analyze the transfer of angular spectrum and fourth-order image formation in two-photon states generated by spontaneous parametric down-conversion in both type I and type II phase matchings. We show how the image transfer from the pump beam to the two-photon field is affected by the anisotropy of the nonlinear crystal and by the coupling between frequency and wave vector. We also show how the distortion produced by the anisotropy can be compensated by the frequency bandwidth in type II phase matching.