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

TL;DR

This paper investigates how evanescent waves interact with sub-wavelength structures to generate retro-reflected waves, using numerical simulations and theoretical analysis, with implications for high-resolution microscopy.

Contribution

It introduces a simple theory explaining retro-reflected wave generation from evanescent interactions and demonstrates control methods via interference effects.

Findings

Evanescent waves are reflected at dielectric interfaces and couple into radiated waves.

A sharp retro-reflected wave peak appears near the structure edge in microscopy images.

The proposed theory is validated through FDTD simulations under various conditions.

Abstract

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.