Limits for superfocusing with finite evanescent wave amplification

TL;DR

This paper establishes a fundamental relation between focus spot size, evanescent wave amplification, and focal length, refining the diffraction limit for superresolution focusing systems and guiding their practical application.

Contribution

It introduces a revised limit for superfocusing based on evanescent wave amplification, aiding comparison and optimization of subwavelength focusing techniques.

Findings

Provides a quantitative relation between focus size and amplification.

Defines when superfocusing surpasses traditional near-field methods.

Guides design choices for superresolution optical systems.

Abstract

Perfect lensing using negative refractive index materials and radiationless electromagnetic interference both provide extreme subwavelength focusing by "amplifying" evanescent wave components that are usually lost. This paper provides a relation between the achievable focus spot size, the amplification available and the focal length. This may be considered as a revised version of Abbe's diffraction limit for focusing systems that have evanescent wave amplification. It is useful in comparing the amplification achieved in various subwavelength focusing implementations, as well as determining when it is better to use existing near-field techniques, such as simple diffraction from an aperture or slit, than to attempt complicated superfocusing.