  Plane EM waves transmitted through nano-corrugated metallic thin films
produce evanescent waves which include the information on the nano-structures.
The production of the evanescent waves at the metallic surface are analyzed. A
microsphere located above the metallic surface collects the evanescent waves
which are converted into propagating waves. The equations for the refraction at
the boundary of the microsphere and the use of Snell's law for evanescent waves
are developed. The magnification of the nano-structure images is explained by a
geometric optics description, but the high resolution is related to the
evanescent waves properties.
