Limitations on Sub-Diffraction Imaging with a Negative Refractive Index   Slab
  Recently it has been proposed that a planar slab of material, for which both the permittivity and permeability have the values of -1, could bring not only the propagating fields associated with a source to a focus, but could also refocus the nonpropagating near-fields, thereby achieving a subdiffraction image. In this work we discuss the sensitivity of the subwavelength focus to various slab parameters, pointing out the connection to slab plasmon modes. We also note and resolve a paradox associated with the perfect imaging of a point source. We conclude that subwavelength resolution is achievable with available technology, but only by implementation of a critical set of design parameters. 
D.R. Smith, D. Schurig, Marshall Rosenbluth, S. Schultz, S. Anantha   Ramakrishna, J.B. Pendry