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The transverse correlation between the pairs of photons produced in optical spontaneous parametric down-conversion is analyzed. The interesting features of the correlation arise from the form of the two-photon state generated in the process. The physics of the rings of radiation emerging from the crystal is described. We discuss the theory behind the recent experiments on two-photon geometric and physical optics. 1996 The American Physical Society.
Morton H. Rubin (Sun,) studied this question.