  Molecular Circular dichroism (CD) spectroscopy faces significant limitations
due to the inherent weakness of chiroptical light-matter interactions. In this
view, resonant optical antennas constitute a promising solution to this problem
since they can be tuned to increase the CD enhancement factor, fCD, a magnitude
describing the electromagnetic near-field enhancement of scatterers associated
with a given helicity. Here, we derive an exact multipolar expansion of fCD,
which is valid to deduce the integrated near-field CD enhancements of chiral
molecules in the presence of scatterers of any size and shape under general
illumination conditions. Based on our analytical findings, we show that the
near-field fCD factor can be related to magnitudes that can be computed in the
far-field, i.e., the scattering cross-section and the helicity expectation
value. Moreover, we show that in the case of lossless cylindrically symmetric
samples, the near-field fCD factor can be inferred experimentally only from two
far-field measurements at specific scattering angles. Our contribution paves
the way for the experimental characterization of devices capable of enhancing
molecular CD spectroscopy.
