  Numerical calculations were performed to examine the mechanisms for
generation of a retro-reflected wave from the interaction of an evanescent wave
with a sub-wavelength structure using the finite-difference time-domain (FDTD)
method. The simulation shows that an evanescent wave is reflected from the
structure at the interface between a high index dielectric material and a low
index material. The reflected evanescent wave couples into the upper medium and
radiates its energy forming a retro-reflected wave, which appears as a sharp
peak near the edge of the structure when imaging the structure in
hyper-numerical-aperture solid immersion microscopy. We propose a simple theory
and verify it through FDTD calculation under various circumstances in order to
explain peculiar features of this phenomenon. Furthermore, we suggest a way to
control the reflection of the evanescent wave by taking advantage of the
interference of the evanescent wave inside the structure.
