  All beams of electromagnetic radiation are made of photons. Therefore, it is
important to find a precise relationship between the classical properties of
the beam and the quantum characteristics of the photons that make a particular
beam. It is shown that this relationship is best expressed in terms of the
Riemann-Silberstein vector -- a complex combination of the electric and
magnetic field vectors -- that plays the role of the photon wave function. The
Whittaker representation of this vector in terms of a single complex function
satisfying the wave equation greatly simplifies the analysis. Bessel beams,
exact Laguerre-Gauss beams, and other related beams of electromagnetic
radiation can be described in a unified fashion. The appropriate photon quantum
numbers for these beams are identified. Special emphasis is put on the angular
momentum of a single photon and its connection with the angular momentum of the
beam.
