Effects of Wavelength Variation on Localized Photoemission in Triangular Gold Antennas

Portland State University

Exposing metal-dielectric structures to light can result in surface plasmon excitation and propagation along the transition interface, creating a surface plasmon polariton (SPP) response. Photoemission electron microscopy (PEEM) has been used to image nanometer scale plasmonic responses in micron-sized plasmonic devices. With PEEM, optical responses can be characterized in detail, aiding in the development of new types of plasmonic structures and their applications. In thin, triangular gold platelets SPPs can be excited and concentrated within specific regions of the material. In this regard, the platelets act as receiver antennas by converting the incident light into localized excitations in specific regions of the gold platelets. The excited areas can be significantly smaller than the wavelength of the incident light (λ ≤ 1 μm). By varying the wavelength of the light, the brightness of the excited spots can be changed, and the electron emission can effectively be switched on or off for a specific region. These experimental findings are directly observed in PEEM imaging and are quantitatively evaluated using a finite-element method (FEM). Our results indicate that in the wavelength range of 600 nm < λ < 800 nm, the electric field strength at the (rear) tip of the gold platelets changes by a factor of ~8, resulting in an intensity change of >60 for single photon excitation processes and a factor of >10³ for 2-photon excitation. Thus, we show that wavelength change is a feasible and effective mechanism for controlling the localized field intensity as well as the photoemission yield.