  It is shown that the transparency of opaque material with negative
permittivity exhibits resonant behavior. The resonance occurs as a result of
the excitation of the surface waves at slab boundaries. Dramatic field
amplification of the incident evanescent fields at the resonance improves the
resolution of the the sub-wavelength imaging system (superlens). A finite
thickness slab can be totally transparent to a \textit{p}-polarized obliquely
incident electromagnetic wave for certain values of the incidence angle and
wave frequency corresponding to the excitation of the surface modes. At the
resonance, two evanescent waves have a finite phase shift providing non-zero
energy flux through the non-transparent region.
