Resonant harmonic generation in AlGaAs nanoantennas probed by cylindrical vector beams

We investigate second- and third-harmonic generation from individual AlGaAs nanoantennas using far-field mapping with radially- and azimuthally-polarized cylindrical vector beams. Due to the unique polarization structure of these beams, we are able to determine the crystal orientation of the nanoantenna in a single scanning map. Our method thus provides a novel and versatile optical tool to study the crystal properties of semiconductor nanoantennas. We also demonstrate the influence of cylindrical vector beam excitation on the resonant enhancement of second- and third-harmonic generation driven by electric and magnetic anapole-like modes, despite falling in the strong absorption regime of AlGaAs. In particular, we observe a greater nonlinear conversion efficiency from a single nanoantenna excited with a radially-polarized beam as compared to an azimuthally polarized cylindrical vector beam. The fundamental field of the radially-polarized beam strongly couples to the multipoles increasing the near-field enhancement of the nanoantenna. Our work introduces new ways to study individual nanostructures and to tailor the efficiencies of nonlinear phenomena at the nanoscale using non-conventional optical techniques.The authors acknowledge the financial support by the Australian Research Council (ARC), the Academy of Finland (287651) and the Tampere University (Investment funding for Optics and Photonics). The authors acknowledge the use of the Australian National Fabrication Facility (ANFF), ACT node. R. C. M. acknowledges a grant from Consejo Nacional de Ciencia y Tecnología (CONACYT), México. L. T. acknowledges the financial support from the Graduate School of Tampere University