Cascaded emission from cold atomic ensembles

We study the phase matched two-photon cascade emission from a collection of cold alkali atoms induced by two color laser excitation. The cascade configuration, which has recently been employed for the generation of polarization-entangled photon pairs at infra-red and telecommunication wavelengths Chaneliere et al. [PRL 96, 093604 (2006) ], exhibits superradiant time scales for the infra-red field component. We will present a theoretical analysis which explain the characteristic features observed.