  This paper develops, in precise quantum electrodynamic terms, photonic
attributes of the "optical chirality density", one of several measures long
known to be conserved quantities for a vacuum electromagnetic field. The
analysis lends insights into some recent interpretations of chiroptical
experiments, in which this measure, and an associated chirality flux, have been
treated as representing physically distinctive "superchiral" phenomena. In the
fully quantized formalism the chirality density is promoted to operator status,
whose exploration with reference to an arbitrary polarization basis reveals
relationships to optical angular momentum and helicity operators. Analyzing
multi-mode beams with complex wave-front structures, notably Laguerre-Gaussian
modes, affords a deeper understanding of the interplay between optical
chirality and optical angular momentum. By developing theory with due
cognizance of the photonic character of light, it emerges that only the spin
angular momentum of light is engaged in such observations. Furthermore, it is
shown that these prominent measures of the helicity of chiral electromagnetic
radiation have a common basis, in differences between the populations of
optical modes associated with angular momenta of opposite sign. Using a
calculation of the rate of circular dichroism as an example, with coherent
states to model the electromagnetic field, it is discovered that two terms
contribute to the differential effect. The primary contribution relates to the
difference in left- and right- handed photon populations; the only other
contribution, which displays a sinusoidal distance-dependence, corresponding to
the claim of nodal enhancements, is connected with the quantum photon
number-phase uncertainty relation. From the full analysis, it appears that the
term "superchiral" can be considered redundant.
