Optical theorem for the conservation of electromagnetic helicity: Significance for molecular energy transfer and enantiomeric discrimination by circular dichroism

We put forward the physical meaning of the conservation equation for the helicity on scattering of an electromagnetic field with a generally magnetodielectric bi-isotropic dipolar object. This is the optical theorem for the helicity that, as we find, plays a role for this quantity analogous to that of the optical theorem for energy. We discuss its consequences for helicity transfer between molecules and for new detection procedures of circular dichroism based on ellipsometric measurements.