Engineering gallium phosphide nanostructures for efficient nonlinear photonics and enhanced spectroscopies

Abstract Optical resonances arising from quasi-bound states in the continuum (QBICs) have been recently identified nanostructured dielectrics, showing ultrahigh quality factors accompanied by very large electromagnetic field enhancements. In this work, we design a periodic array of gallium phosphide (GaP) elliptical cylinders supporting, concurrently, three spectrally separated QBIC with in-plane magnetic dipole, out-of-plane and electric quadrupole characters. We numerically explore system for second-harmonic generation degenerate four-wave mixing, demonstrating giant per unit cell conversion efficiencies up to ? 2 W ?1 60 ?2 , respectively, when considering realistic introduced asymmetries metasurface, compatible current fabrication limitations. find that configuration outperforms more than four orders magnitude response low-Q Mie or anapole individual GaP nanoantennas engineered nonlinear mode-matching conditions. Benefiting straight-oriented one examined high-Q resonances, further propose novel nanocavity enhanced spectroscopies slotting meta-atoms array. discover optical cavity sustains high-intensity fields homogeneously distributed inside slot, delivering its best performance are cut end forming gap, which represents convenient model experimental investigations. When placing an point dipole added aperture, metasurface offers radiative enhancements, exceeding previously reported slotted dielectric nanodisk at excitation two magnitude.