PHASE-DIFFERENCE OPERATOR

We introduce a unitary operator representing the exponential of the ph ase difference between two modes of the electromagnetic field. The eig envalue spectrum has a discrete character that is fully analyzed. We r elate this operator with a suitable polar decomposition of the Stokes parameters of the field, obtaining a natural classical limit. The case s of weakly and highly excited states are considered, discussing to wh at extent it is possible to talk about the phase for a single-mode fie ld. This operator is applied to some interesting two-mode fields.