Two-photon interference in micro- and macro-systems

Two-photon correlations are discussed within the formalism of Hanbury-Brown and Twist interferometry and Bose-Einstein correlations. The technique is presented as a universal tool to study the properties of any boson source - light sources such as stars, or photon and meson sources in the early phase of heavy-ion collisions. The method is illustrated using experimental data on photon-pair production in nuclear reactions, available only in the intermediate (several tens of MeV/N) energy domain. The observed interference signals is interpreted in terms of source size and reaction dynamics. (author)