On the optimum form of an aperture for a confinement of the optically excited electric near field

Abstract

SummaryA triangular nanoaperture in an aluminium film was used previously as a probe in a scanning near-field optical microscope to image single fluorescent molecules with an optical resolution down to 30 nm. The high-resolution capability of the triangular aperture probe is because of a highly confined spot of the electric near field which emerges at an edge of the aperture, when the incident light is polarized perpendicular to this edge. Previous numerical calculations of the near-field distribution of a triangular aperture in a planar metal film using the field susceptibility technique yielded a nearly quantitative agreement with the experimental results. Using the same numerical technique we now explored the possibility for a further confinement of the electric near field and an increase in its intensity by modifications of the form of a triangular aperture. By introducing a kink on an edge pointing into the aperture, an arrow-shaped aperture is formed with one convex and three concave metal corners. It turns out that this form leads to a substantial further confinement of the near-field intensity at the convex corner. By extending the wings of this arrow-shaped aperture a further 5-fold increase of the intensity can be obtained without a deterioration of the confined spot.

Zero-mode waveguide nanophotonic structures for single molecule characterization

“…The shape [ 57 ] and metal used [ 58 ] to construct the nanopore are also important factors in determining the ability of the waveguide to confine the electromagnetic field, important for determining the optimum conditions for fluorescence, which change depending on the desired excitation and emission wavelengths. The cross-sectional shape of the nanopore/nanoantenna, e.g.…”

Electromagnetic Near-Field Nanoantennas for Subdiffraction-Limited Surface Plasmon-Enhanced Light Microscopy

“…We emphasize, however, that these approaches rely on excitation and localization of SPs based on extraordinary transmission and in general do not satisfy (3). While TIR formed at inclined incidence may provide an optimum confinement of a hot spot in the lateral plane [49], production of a symmetric hot spot can be tricky because the incident light wave vector that creates SPs is inclined in the lateral plane. If a PSF provided by such a hot spot is elliptical, FWHM of the long axis can limit the imaging resolution.…”

Novel SNOM Probes Based on Nanofocusing in Asymmetric Structures

“…Such methods have been extensively used to investigate novel aperture shapes using, for example, the finite difference time domain method (FDTD) or the field susceptibility technique and in most of the cases considering apertures in thin metal films [21,24,[26][27][28]. Furthermore, the analysis of wave propagation in tapered structures (either traditional conical tapers or structures modified with corrugations or multiple tapers) with an aperture at the end has been carried out using the finite difference beam propagation method [65], the FDTD method [18,19], the body of revolution FDTD method (BOR-FDTD) [48], the multiple multipole method (MMP) [66].…”

“…Another route followed for the improvement of the performance of aperture probes has been the implementation of other aperture shapes different from the typical circular design: rectangular, square, slit, elliptical, C-shaped, I-shaped or dumbbell, H-shaped, bowtie, connected and separated double aperture, triangular, rod hole and tooth hole, gap apertures have been analysed and/or fabricated in fiber-and cantilever-based probes [20][21][22][23][24][25][26][27][28]. The improved throughput and field localization for some preferential input polarizations is due to the strong asymmetry of such aperture shapes and to the excitation of SPPs.…”