  Numerical results for the distributions of light transmitted through metallic
planar lenses composed of symmetric nanogroove arrays on the surfaces of a gold
film are presented and explained. Both the near- and far-field distributions of
the intensity of light transmitted are calculated by using a Green's function
formalism. Results for an optimal transverse focus based on a quadratic
variation of groove width are obtained. Meanwhile, a significant dependence of
the focal length on the wavelength of light incident from the air side through
the gold film into a dielectric substrate is found for this detector
configuration.
