Dependence on crystal parameters of the correlation time between signal and idler beams in parametric down conversion calculated in the Wigner representationA. Casado, A. Fernández-Rueda, T. Marshall, J. Martínez, R. Risco-Delgado and E. SantosEur. Phys. J. D, 11 3 (2000) 465-472DOI: https://doi.org/10.1007/s100530070074