  Theoretical model of the enhanced optical resolution of the surface plasmon
immersion microscope is developed, which is based on the optics of surface
plasmon Bloch waves in the tightly bound approximation. It is shown that a
similar resolution enhancement may occur in a more general case of an immersion
microscope based on photonic crystal materials with either positive or negative
effective refractive index. Both signs of the effective refractive index have
been observed in our experiments with surface plasmon immersion microscope,
which is also shown to be capable of individual virus imaging.
