Far Infrared Slab Lensing and Subwavelength Imaging in Crystal Quartz
  We examine the possibility of using negative refraction stemming from the phonon response in an anisotropic crystal to create a simple slab lens with plane parallel sides, and show that imaging from such a lens should be possible at room temperature despite the effects of absorption that are inevitably present due to phonon damping. In particular, we consider the case of crystal quartz, a system for which experimental measurements consistent with all-angle negative refraction have already been demonstrated. Furthermore, we investigate the possibility of subwavelength imaging from such materials, and show that it should be possible for certain configurations. 
R. Estev\^am da Silva, R. Mac\^edo, T. Dumelow, J. A. P. da Costa, S.   B. Honorato and A. P. Ayala
physics.optics cond-mat.other