Second-harmonic spectroscopy with structured beams and the observation of quasi-BIC modes in all-dielectric nanoresonators

Abstract

We report on the experimental and numerical results for the second-harmonic generation spectroscopy by doughnut-shaped cylindrical vector beams of azimuthal and radial polarizations in individual subwavelength AlGaAs particles, which support multipolar Mie resonances at the fundamental and double frequencies. We observe high-Q resonant optical modes associated with bound states in the continuum for the azimuthally polarized pump beam with the record-high efficiency (0.1%) of the up-conversion nonlinear optical process due to a strong electromagnetic field confinement. Our findings provide an important step towards a design of resonant subwavelength all-dielectric nanostructures with tailored efficiencies of nonlinear optical phenomena at the nanoscale. Show more