title: Fermat's principle and the formal equivalence of local light-ray rotation and refraction at the interface between homogeneous media with a complex refractive index ratio.
abstract: We derive a formal description of local light-ray rotation in terms of complex refractive indices. We show that Fermat's principle holds, and we derive an extended Snell's law. The change in the angle of a light ray with respect to the normal of a refractive index interface is described by the modulus of the refractive index ratio; the rotation around the interface normal is described by the argument of the refractive index ratio.
authors.affiliation: Department of Physics and Astronomy, Faculty of Physical Sciences, University of Glasgow, Glasgow, UK.
authors.forename: Bhuvanesh
authors.initials: B
authors.lastname: Sundar
authors.forename: Alasdair C
authors.initials: AC
authors.lastname: Hamilton
authors.forename: Johannes
authors.initials: J
authors.lastname: Courtial