# Penetration depth reduction with plasmonic metafilms

## TL;DR

This paper demonstrates that ultrathin plasmonic metafilms can significantly reduce electromagnetic penetration depth compared to traditional metal films, enhancing optical device performance.

## Contribution

It introduces a novel metafilm design that decreases penetration depth via enhanced effective mass in photonic band structure, improving reflectivity and waveguide density.

## Key findings

- Penetration depth is significantly reduced in the proposed metafilm.
- Enhanced effective mass in photonic band structure causes the reduction.
- Potential applications include ultrathin reflectors and denser plasmonic waveguides.

## Abstract

In many optical systems, including metal films, dielectric reflectors, and photonic crystals, electromagnetic waves can experience evanescent decay. The spatial length scale of such decay defines the penetration depth. The ability to reduce the penetration depth is important for a number of applications in free-space and integrated photonics. In this paper, we consider a ultrathin metafilm structures consisting of alternating regions of metal and dielectric. We show that the penetration depth of such metafilm can be significantly smaller as compared to that of a corresponding metal thin film. The reduction of the penetration depth arises due to the enhanced effective mass in the photonic band structure. This effect can be used to enhance the reflectivity of ultrathin reflectors, and to increase the packing density of subwavelength plasmonic waveguides.