Characterization of Airy Surface Plasmon Polaritons by Photoemission Electron Microscopy

IntroductionAiry surface plasmon polaritons (SPPs) are propagating surface plasmon excitations that are confined to the metal-dielectric interface, containing the properties of Airy beams. The generation of such... [ view full abstract ]

Introduction

Airy surface plasmon polaritons (SPPs) are propagating surface plasmon excitations that are confined to the metal-dielectric interface, containing the properties of Airy beams. The generation of such non-diffracting beams that are suitable for flat land photonics has always been of interest. It opens up new capabilities in prominent device application, e.g., optical traps and tweezers, biosensors, selective on-chip manipulation of nanoparticles.

Here, we report a versatile method of the investigation of Airy SPPs on a metallic surface by PhotoEmission Electron Microscopy (PEEM). It can provide a spatial resolution of the order of 20nm. PEEM allows for direct visualization of the plasmon field through photoemission, where the photo-emitted electrons provide a map of electromagnetic fields at the surface.

Methods

Our sample design is inspired by Minovich et al. and was realized by focused ion beam milling into a 200 nm thick gold film. This specially designed diffraction grating can generate the Airy beam profile and simultaneously can couple free space propagating waves to SPPs. For the illumination, we used a home-built tunable optical parametric chirped pulse amplifier. The central wavelength was varied between 690 and 840 nm. The emitted photoelectrons were imaged by a PEEM from Focus GmbH. Large-scale 3D finite difference time domain simulations were performed to optimize and theoretically verify the design.

Results

Both theory and experiment show an excellent agreement. On the air-gold interface, the Airy SPP is launched at the grating edge and simultaneously interferes with the incident laser pulse. The photo-emitted electrons provide the direct visualization of the total field. The area of constructive and destructive interference leads to higher and lower nonlinear photoemission yield. This result clearly shows SPP generation containing all the properties of Airy beams. The main lobe of the Airy SPP propagates along a curved trajectory for more than 25μm.

In conclusion, we have experimentally investigated the Airy plasmons with high spatial resolution, and their propagation along the curved trajectory has been visualized. The experimental results not only match with theoretical results but also contain deeper insight into the structure.