Generation of a retro-reflected wave by interaction of an evanescent wave with a sub-wavelength structure

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.