8 research outputs found
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Multipolar second-harmonic generation from high-Q quasi-BIC states in subwavelength resonators
We put forward the multipolar model which captures the physics behind linear and nonlinear response driven by high-quality (high-Q) supercavity modes in subwavelength particles. We show that the formation of such trapped states associated with bound states in the continuum (quasi-BIC) can be understood through multipolar transformations of coupled leaky modes. The quasi-BIC state appears with increasing the order of the dominating multipole, where dipolar losses are completely suppressed. The efficient optical coupling to this state in the AlGaAs nanodisk is implemented via azimuthally polarized beam illumination matching its multipolar origin. We establish a one-to-one correspondence between the standard phenomenological non-Hermitian coupled-mode theory and multipolar models. The derived multipolar composition of the generated second-harmonic radiation from the AlGaAs nanodisk is then validated with full-wave numerical simulations. Back-action of the second-harmonic radiation onto the fundamental frequency is taken into account in the coupled nonlinear model with pump depletion. A hybrid metal-dielectric nanoantenna is proposed to augment the conversion efficiency up to tens of per cent due to increasing quality factors of the involved resonant states. Our findings delineate novel promising strategies in the design of functional elements for nonlinear nanophotonics applications
Multipolar second-harmonic generation from high-Q quasi-BIC states in subwavelength resonators
We put forward the multipolar model whichcaptures the physics behind linear and nonlinear responsedriven by high-quality (high-Q) supercavity modes in sub-wavelength particles. We show that the formation ofsuch trapped states associated with bound states in thecontinuum (quasi-BIC) can be understood through multi-polar transformations of coupled leaky modes. The quasi-BIC state appears with increasing the order of the domi-nating multipole, where dipolar losses are completely sup-pressed. The efficient optical coupling to this state in theAlGaAs nanodisk is implemented via azimuthally polarizedbeam illumination matching its multipolar origin. Weestablish a one-to-one correspondence between the stan-dard phenomenological non-Hermitian coupled-modetheory and multipolar models. The derived multipolarcomposition of the generated second-harmonic radiationfrom the AlGaAs nanodisk is then validated with full-wavenumerical simulations. Back-action of the second-harmonicradiation onto the fundamental frequency is taken into ac-count in the coupled nonlinear model with pump depletion.A hybrid metal-dielectric nanoantenna is proposed toaugment the conversion efficiency up to tens of per cent dueto increasing quality factors of the involved resonant states.Ourfindings delineate novel promising strategies in thedesign of functional elements for nonlinear nanophotonics applications
Multipolar analysis of second-harmonic generation in (111) Gallium Arsenide nanoparticles
We perform multipolar analysis of second-harmonic generation (SHG) from (111)-grown gallium arsenide (GaAs) nanoantennas and discuss its specifics. It was experimentally demonstrated that the conversion efficiency in axially-symmetric (111) GaAs nanoparticles remains constant under the polarization rotation of normally incident radiation in a wide range of particle sizes, while the SHG radiation pattern changes. We apply the analytical method based on the Lorentz lemma to explain this behaviour. The induced nonlinear current is decomposed into two rotating contributions, which are shown to generate multipoles of different parities. Thus, the total SHG intensity in the far-field is proved to be independent of the in-plane rotation of the pump polarization. Nevertheless, due to the threefold symmetry of the crystal with regard to the (111) direction, the SHG radiation pattern rotates around the polar axis repeating its shape every 60°.publishedVersionPeer reviewe