Nonlinear-optical microscopy of asymmetric-shaped nanoantennas

Abstract

Arrays of metal nanostructures have attracted much interest due to their unique potential as optical nanoantennas and nanosensors. Here we use the second harmonic generation (SHG) microscopy technique for the studies of the nonlinear optical (NLO) response of cobalt nanoparticles of triangular and trapezoid shapes separated from a Py/Si3N4 film by a 1.5 nm thick MgO spacer. We demonstrate that the nonsymmetric elongated shape of planar nanoparticles along with the strong light localization effects result in the enhancement of the NLO response, including SHG and two-photon fluorescence. We also demonstrate that the efficiency of the SHG in nanoparticles is rather sensitive to the polarization of the incident laser beam, the visibility of the nanostructures in the nonlinear microscopy images being the highest for the linear polarization of the laser beam.