Transverse spatial and frequency properties of two-photon states generated by spontaneous parametric down-conversion

We present a detailed account of the two-photon states generated by SPDC in both type I and type II phase matching, including the effects of anisotropy of the nonlinear medium and the frequency spread of the down-converted fields. Accurate as well as simplified expressions are derived for type I and type II phase matching in the context of Fourier Optics. The main results are compared with experimental data available in the literature, showing good agreement in all cases.