Phase and intensity correlations produced by second-order non-linear interactions: from holographic imaging to ghost imaging

We discuss coherence properties of optical fields interacting via second-order non-linear polarization and their roles in procedures of image transfer and/or image reconstruction, including ghost-imaging. First-order coherence (phase correlations) is the key for the realization of real-time holographic image reconstruction, while second-order coherence (intensity correlations) allows ghost-imaging. We demonstrate these imaging properties for a single phase-matched chi^(2)-interaction and for two simultaneously phase-matched chi^(2)-interactions, which are interlinked by the participation of one of the fields to both interactions.