Strong coupling between mid-infrared localized plasmons and phonons.

Xiaodong Yang,Weiwei Wan,Jie Gao

doi:10.1364/oe.24.012367

Xiaodong Yang, Weiwei Wan + Show 1 more

Open Access

https://doi.org/10.1364/oe.24.012367

Copy DOI

Abstract

We numerically and experimentally demonstrate strong coupling between the mid-infrared localized surface plasmon resonances supported by plasmonic metamaterials and the phonon vibrational resonances of polymethyl methacrylate (PMMA) molecules. The plasmonic resonances are tuned across the phonon resonance of PMMA molecules at 52 THz to observe the strong coupling, which manifests itself as an anti-crossing feature with two newly formed plasmon-phonon modes. It is also shown that the forbidden energy gap due to mode splitting is proportional to the overlapped optical power between the plasmonic resonance mode and the PMMA molecules, providing an effective approach for manipulating the coupling strength of light-matter interaction.

Highlights

Metamaterials are artificially engineered structures designed to exhibit extraordinary optical properties that are not achievable in natural materials
The middle panel shows that the plasmonic resonance frequency is red shifted to ωm = 52 THz for the uncoupled metamaterials coated with a 180-nm-thick polymethyl methacrylate (PMMA) film but in absence of the phonon vibrational resonance, where the permittivity of PMMA is assumed to be a constant without taking into account the phonon mode
Since the coupling strength depends on both the plasmonic near field intensity and the overlapped mode volume with PMMA molecules, the amount of the overlapped optical power Ptot described in Eq (1) is proportional to the forbidden energy gap Ω as a function of the PMMA thickness, which can be calculated as, Ω = B(1− exp(−2α z)) + B0, (2)

Summary

Introduction

Metamaterials are artificially engineered structures designed to exhibit extraordinary optical properties that are not achievable in natural materials. Plasmonic metamaterials supporting localized surface plasmon resonances (LSPRs) can confine the electromagnetic fields at the subwavelength scale and greatly enhance the near-field coupling effects and the light-matter interactions Such capability of plasmonic metamaterials enables many biosensing applications such as surface-enhanced Raman scattering (SERS) [10] and surfaceenhanced infrared absorption (SEIRA) [11]. The coupling between plasmonic resonances and phonon vibrational resonances of molecules through near field interactions can give rise to a new set of splitting plasmon-phonon modes with anti-crossing behavior [21,22,23]. Such strong coupling can be realized by using the Fabry-Pérot cavity [24]. It is shown that the mode coupling strength can be controlled by the variation of the thickness of PMMA layer

Strong coupling between plasmonic metamaterials and PMMA molecules

Tuning the forbidden energy gap by varying the thickness of PMMA layer

Findings

Conclusion