title: Phase transition in a radiation-matter interaction with recoil and collisions.
abstract: The standard model introduced to describe the collective atomic recoil of an ensemble of atoms interacting with a strong electromagnetic field has been here extended by the inclusion of collisions with a buffer gas. As a result, we find that in the thermodynamic limit the coherent emission of radiation exhibits a continuous phase transition upon increasing the pump intensity. The output laser field is strictly larger than 0 only above a critical value. We find that the transition is not associated with the onset of spatial ordering but rather with the onset of a synchronization between the polarization phase and spatial position. A coherence parameter is introduced to characterize the phase transition.
authors.affiliation: Institut Non Linéaire de Nice, UMR 6618 CNRS, Université de Nice-Sophia Antipolis, 1361 Route des Lucioles, F-06560 Valbonne, France.
authors.forename: M
authors.initials: M
authors.lastname: Perrin
authors.forename: G L
authors.initials: GL
authors.lastname: Lippi
authors.forename: A
authors.initials: A
authors.lastname: Politi