Dr. Vladimir Agranovich

University of Texas at Dallas

Institute of Spectroscopy, Russian Academy of Science

Negative Refraction, Polarions and Group Velocity

Monday, October 22, 2007

4:00 p.m.

Cardwell 102

Negative 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.  These systems are analyzed in a unified way provided by the spatial dispersion framework. The framework utilizes the notion of the generalized dielectric tensor  representing the electromagnetic 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.