University of Texas at Dallas
Institute of Spectroscopy,
Russian Academy of Science
Refraction, Polarions and Group Velocity
October 22, 2007
refraction occurs at interfaces as a natural
consequence of the negative group velocity of waves in one of the
interfacing media. The historical origin of this understanding of
the phenomenon is briefly discussed. We consider several physical systems that
may exhibit normal electromagnetic waves
(polaritons) with negative group velocity at optical frequencies.
systems are analyzed in a unified way provided by
the spatial dispersion framework. The framework utilizes the
notion of the generalized dielectric tensor
response of the medium to perturbations of
frequency and wave vector. Polaritons with negative group
velocity can exist in continuous media (whether in natural or in artificial
meta-materials) with a sufficiently strong spatial dispersion.
Our examples include natural both gyrotropic and nongyrotropic systems, and bulk
and surface polariton waves.