Precise laser-cutting of single silver nanowires for direct measurement of SPPs propagation losses

Abstract

This work presents an alternative experimental approach to directly measure propagation losses of surface plasmon polaritons (SPPs) in a single silver nanowire (AgNW). The methodology synergistically combines several techniques, including single nanowire optical shaping, accurate triggering of SPPs by upconversion nanocrystals (NCs), and precise deposition of sub-micrometer-size droplets with emitters. Indeed, a femtoliter volume of colloidal NCs deposited at one end of the nanowire and excited with a laser through an objective provides a stable source of polaritons, which propagate in the nanowire. The intensity of radiation released by the SPPs scattered out at the opposite AgNW end is a direct measure of propagation losses. This is enabled through a method of precise laser cutting of the nanowire, where the length of the nanowire can be gradually reduced by an optically controlled melting process. At the same time, both the length and diameter of the nanowire are constantly monitored using optical imaging of the complex interaction between the nanowire and polarized Gaussian beam. The optical cutting technique, implemented in this experiment, shows great potential for advanced and inexpensive shaping of the metallic nanostructures for nanophotonic applications.