The approach which has been proposed by one of us [Optics Comm. 136 (1
997) 219] is developed. The quantum phase properties of radiation are
determined via the conservation of the angular momentum in the interac
tion with a source. It is shown that the use of two dual representatio
ns of the angular momentum of the dipole transition leads to the defin
ition of five operators similar in some sense to the Stokes operators
of the radiation. The approach is compared with that by Pegg and Barne
tt [20]. (C) 1998 Elsevier Science B.V.