Optimised low-loss multilayers for imaging with sub-wavelength resolution in the visible wavelength range

TL;DR

This paper presents optimized multilayer structures using silver and various dielectrics to achieve high transmission and sub-wavelength resolution in visible light imaging, outperforming traditional design methods.

Contribution

It introduces a novel optimization approach for multilayer designs that surpasses effective medium theory-based methods in resolution and transmission performance.

Findings

Optimized Ag-GaP multilayer achieves 78% transmission and 60 nm resolution.

Optimized multilayers outperform simple designs based on effective medium theory.

Effective medium theory leads to sub-optimal designs for structures with periods over 40 nm.

Abstract

We optimise the effective skin-depth and resolution of Ag-TiO2, Ag-SrTiO3, and Ag-GaP multilayers for imaging with sub-wavelength resolution. In terms of transmission and resolution the optimised multilayers outperform simple designs based on combined use of effective medium theory, impedance matching and Fabry-Perot resonances. For instance, an optimised Ag-GaP multilayer consisting of only 17 layers, operating at the wavelength of 490 nm and having a total thickness equal to one wavelength, combines 78% intensity transmission with a resolution of 60 nm. It is also shown that use of the effective medium theory leads to sub-optimal multilayer designs with respect to the trade-off between the skin depth and resolution already when the period of the structure is on the order of 40 nm or larger.