title: Orbital angular momentum of entangled counterpropagating photons.
abstract: We elucidate the paraxial orbital angular momentum of entangled photon pairs generated by spontaneous parametric downconversion in different noncollinear geometries in which the entangled photons counterpropagate. We find, in particular, the orbital angular momentum of entangled pairs generated in transverse-emitting configurations, in which none of the known rules for selecting orbital angular momentum holds.
authors.affiliation: Institut de Ciencies Fotoniques, and Department of Signal Theory and Communications, Universitat Politecnica de Catalunya, 08034 Barcelona, Spain. jperez@tsc.upc.es
authors.forename: Juan P
authors.initials: JP
authors.lastname: Torres
authors.forename: Clara I
authors.initials: CI
authors.lastname: Osorio
authors.forename: Lluis
authors.initials: L
authors.lastname: Torner