Ian Schick

Interference and resonant cavity effects explain enhanced transmission through subwavelength apertures in thin metal films.

Transmission through an opaque Au film with a single subwavelength aperture centered in a smooth cavity between linear grating structures is studied experimentally and with a finite element model. The model is in good agreement with measured results and is used to investigate local field behavior. It shows that a surface plasmon polariton (SPP) is launched along the metal surface, while interference of the SPP with the incident light along with resonant cavity effects give rise to suppression and enhancement in transmission. Based on experimental and modeling results, peak location and structure of the enhancement/suppression bands are explained analytically, confirming the primary role of SPPs in enhanced transmission through small apertures in opaque metal films.

Theoretical study of enhanced transmission through subwavelength linear apertures flanked by periodic corrugations

Enhanced transmission through structures consisting of linear gratings surrounding a single subwavelength aperture in an opaque gold film is modeled using a commercial finite element model (FEM). The stability of the FEM and boundary conditions are discussed, and different field visualizations are explored to gain insight into field behavior. The results from the FEM were compared with experimental results, yielding excellent agreement. This lends confidence that the FEM is giving an accurate representation of the field behavior around the structure. The FEM was then used to examine how transmission enhancement depends on geometric properties of the structure and to gain insight into the mechanisms of transmission enhancement.

Explaining enhanced optical transmission through sub- wavelength apertures: Surface plasmon polaritons vs. composite diffracted evanescent waves

Surface plasmon polaritons¿ (SPPs) and composite diffracted evanescent waves¿ (CDEWs) role in enhanced optical transmission are reviewed experimentally, via numerical modeling, and theoretically. All results support involvement of SPPs and contradict the existence of CDEWs.

Method to compensate for fluctuations in optical power delivered to a near-field scanning optical microscope

Near-field scanning optical microscopy (NSOM) is a scanning probe technique that uses a tapered optical fiber to probe optical characteristics of a surface in registry with topography. Light can either be injected into the sample or collected from the sample via the subwavelength aperture formed at the tip of the probe. While operating in injection mode, variations in the optical power delivered to the probe, and consequently variations in the optical flux through the aperture, place limits on the imaging of spatial variations in optical properties. We present a novel method utilizing bend loss in an optical fiber to correct for variations in the optical flux of the aperture of a NSOM probe.