Tailored Hotspots from Airy-Based Surface Plasmon Polaritons

Abstract

Surface plasmons have attracted growing interest from the photonics community due to their inherent ability to controllably confine light below the diffraction limit and their direct application in trapping and transporting matter at the nanoscale. This method, known as plasmonic tweezers, employs confined fields generated by either localized plasmons or surface plasmon polaritons (SPP), which originate in the vicinity of nanostructure-based traps or across structureless platforms, respectively. Herein, we present a new theoretical method for generating intense light hotspots and engineering their features by overlapping Airy SPPs (ASPP) at a smooth dielectric-metal interface. We coherently add pairs of Hermite-Gauss modes that belong to a novel complete basis set of finite-energy ASPPs, which yield highly confined plasmonic hotspots ($\approx λ$/10) without the need of using any nanostructured platform. Mode order and relative spacing parameters can be used to tailor the intensity and quality factor of said hotspots, largely outperforming their Gaussian-only-based counterparts. Our method opens a promising venue to confine light at the nanoscale using ASPP-based structured light, which helps to advance the development of structureless plasmonic tweezers and holds promising potential for its application in optical signal processing and plasmonic circuitry.

Figures (4)

• Figure 1: (a)-(b) Density plots of the intensity of two overlapping ASPPs at a silver-air interface with $n=1$ and inter-beam separations equal to (a) $x_0=0.9$$\mu$m and (b) $x_0=1.4$$\mu$m. Plots of the intensity cross-sections that intersect the hotspot in map (a) along the $z$ propagation direction (c) and the $x$ transverse direction (d). The black, blue and red cross sections presented in (d) are extracted at $z_{black}=620$ nm, $z_{blue}=620$ nm and $z_{red}=770$ nm.
• Figure 2: (a)-(d) Density plots of the intensity of two overlapping APPS at a silver-air interface as a function the propagation $z$ and transverse $x$ directions for $n$=0-3, respectively. The $x_0$ separations were chosen to provide the most intense hotspots for each order $n$.
• Figure 3: Density plots of the intensity of hotspots as a function of the propagation direction $z$ and the separation $x_0$ between two overlapping APPS at a silver-air interface. The (a)-(d) panels illustrate maps corresponding to $n$=0-3, respectively. The insets display $I_n$-$z$ profiles for separations $x_0$ at which the so-generated hotspots have a maximum intensity.
• Figure 4: Graphs of the (a) hotspot intensity and (b) position along the propagation direction $z$ as a function of the separation $x_0$ between two overlapping APPS for $n$=0-3. The dashed black line is a fit to the data.