Revisiting the perfect lens with loss

We reconsider the refraction of evanescent waves at an interface between air and a negative index medium under the assumption that the negative index medium is necessarily dispersive and lossy. We show that all evanescent waves in air will be refracted into decaying propagating waves inside the negative index medium, with different spatial frequency components having different propagation directions and separated both in time and space; hence no refocus of these evanescent waves is possible. Accordingly, all information encoded by evanescent waves will be lost in the image making sub-diffraction-limited imaging impossible.