Three-dimensional mapping of optical near field of a nanoscale bowtie antenna

Abstract

Ridge nanoscale aperture antennas have been shown to be a high transmission nanoscale light source. They provide a small, polarization-dependent near-field optical spot with much higher transmission efficiency than circularly-shaped apertures with similar field confinement. This provides significant motivations to understand the electromagnetic fields in the immediate proximity to the apertures. This paper describes an experimental three-dimensional optical near-field mapping of a bowtie nano-aperture. The measurements are performed using a home-built near-field scanning optical microscopy (NSOM) system. An aluminum coated Si(3)N(4) probe with a 150 nm hole at the tip is used to collect optical signals. Both contact and constant-height scan (CHS) modes are used to measure the optical intensity at different longitudinal distances. A force-displacement curve is used to determine the tip-sample separation distance allowing the optical intensities to be mapped at distances as small as 50 nm and up to micrometer level. The experimental results also demonstrate the polarization dependence of the transmission through the bowtie aperture. Numerical simulations are also performed to compute the aperture's electromagnetic near-field distribution and are shown to agree with the experimental results.

A Review of Three-Dimensional Scanning Near-Field Optical Microscopy (3D-SNOM) and Its Applications in Nanoscale Light Management

“…From the 3D SNOM scans the near-field can be seen to extend up to 20 nm from the film surface, at which point it drops off sharply in intensity. The optical phase image (Figure 11b) clearly identifies a 180° phase shift that is characteristic of bowtie apertures, and extends past the near-field boundary seen in the amplitude image [50,51].…”

“…In the following section, applications of 3D SNOM compared to traditional 2D scanning are discussed, with examples of the use of 3D SNOM to study and improve the design of organic solar cells, nano-aperture antennas, nanoparticle arrays, and photonic crystal waveguides [28,29,34,[48][49][50][51][52]. Figure 5 illustrates the equipment setup that can be used for 3D SNOM measurements.…”

“…pattern observed in the SNOM image is a consequence of light originating from the surface that is back scattered from the tip itself and reflected from the Au surface to be collected by the tip. Nano antennas or apertures with more exotic shapes such as the bowtie antenna [50,51] have been sought after for their light scattering properties. Bowtie shaped antennas are designed to produce enhanced electric fields in the aperture between the two bowtie halves.…”

Nanophotonic approaches for nanoscale imaging and single‐molecule detection at ultrahigh concentrations

“…Bowtie nanoaperture antennas (BNA) carved at the end facet of tapered aluminum‐coated optical fibers provide a more robust and alternative design to monopole antennas. These nanostructures consist of two triangle openings faced tip‐to‐tip and separated by a small opening gap providing a superconfined spot with an intense local field and broadband response in the visible regime (Guo et al, ). Moreover, the effective confinement region of BNAs can be readily tuned by controlling the excitation polarization (Guo et al, ; Mivelle et al, ).…”

Three-dimensional mapping of optical near field with scattering SNOM

“…There have been a significant amount of efforts dedicated to visualizing the optical near field distribution of plasmonic structures, especially by applying scanning near-field optical microscopy (SNOM). For example, with aperture type SNOM, the optical near field distribution of bowtie apertures has been mapped in both two and three dimensions [8,9] at visible wavelength. The scattering-type SNOM (s-SNOM) can achieve higher resolution, on the order of 10 nm, and acquire both amplitude and phase information simultaneously [10].…”