The Surface response around a sharply resonant surface polariton mode is simply a Lorentzian

TL;DR

The paper demonstrates that the surface response near a sharp surface polariton resonance can be accurately modeled with a simple Lorentzian function, revealing a direct link between dispersive and dissipative effects.

Contribution

It introduces a Lorentzian approximation for the surface response at resonances, simplifying analysis and highlighting the correlation between real and imaginary parts of the response.

Findings

Lorentzian model accurately describes surface response near resonance

Strong correlation between dispersive and dissipative effects

Applicable to various materials like sapphire, CaF2, BaF2

Abstract

At the planar interface between a material and vacuum, the complex surface response S(omega)=[eps(omega) 1]/[eps(omega)+1], with eps(omega) the relative complex dielectric permittivity of the material, exhibit resonances, typical of the surface polariton modes, when eps(omega) ~ 1. We show that for a moderately sharp resonance, S(omega) is satisfactorily described with a mere (complex) Lorentzian, independently of the details affecting the various bulk resonances describing ) eps(omega). Remarkably, this implies a quantitative correlation between the resonant behaviors of Re[S(omega)] and Im[S(omega)], respectively associated to dispersive and dissipative effects in the surface near-field. We show that this "strong resonance" approximation easily applies, and discuss its limits, based upon published data for sapphire, CaF2 and BaF2. Extension to interfaces between two media or to a non planar interface is briefly considered.