  Numerical study of evanescent fields in an isotropic backward-wave (BW)
(double negative or "left-handed") slab is performed with the FDTD method. This
system is expected to be able to restore all spatial Fourier components of the
spectrum of a planar source, including evanescent fields, realizing a
"superlens". The excitation of surface modes on the interfaces of the slab,
which is the key process responsible for the sub-wavelength focusing, is
numerically confirmed and the time-domain field behavior is studied. In
particular, a numerical verification of the amplification of evanescent modes
by an isotropic BW slab with epsilon=mu=-1 is provided.
