Spontaneous radiation of a finite-size dipole emitter in hyperbolic   media
  We study the radiative decay rate and Purcell effect for a finite-size dipole emitter placed in a homogeneous uniaxial medium. We demonstrate that the radiative rate is strongly enhanced when the signs of the longitudinal and transverse dielectric constants of the medium are opposite, and the isofrequency contour has a hyperbolic shape. We reveal that the Purcell enhancement factor remains finite even in the absence of losses, and it depends on the emitter size. 
Alexander N. Poddubny, Pavel A. Belov and Yuri S. Kivshar
physics.optics