Boosting nonlinear frequency conversion in extremely confined volumes remains a crucial task in nano-optics, all-optical signal processing and nanomedicine. Photon-photon interactions at the nanoscale are intrinsically weak and can only be excited using very high light intensities. Optical materials featuring large nonlinearities and low absorption losses offer a valuable solution to circumvent this limitation and effectively generate nonlinear effects in nanoscale volumes. Metal-less nanophotonics has recently raised an increasing interest because the optical response of high-permittivity dielectric nanoparticles exhibits negligible dissipative losses and strong magnetic multipole resonances in the visible and near-IR. We have recently proposed all-dielectric AlGaAs-on-AlOx nanodisks and coupled dimers featuring an intense second harmonic generation (SHG) with conversion efficiency up to 10-^5 upon pumping with an ultrafast Erbium-doped fiber laser centered at 1554 nm (150 fs pulses, 80 MHz repetition rate) at 1.6 GW/cm^2 fluency, which is in excellent agreement with our numerical simulations.
To further enhance the SHG efficiency, we propose a metal-dielectric hybrid nanostructure based on a nanodisk surrounded by a gold plasmonic nanoring. The role of the plasmonic nanoantenna is to efficiently collect the illumination light and convert it to match the anapole mode supported by the AlGaAs nanodisk, to significantly amplify the electric field inside the disk. We theoretically predict and experimentally demonstrate that the SHG conversion efficiency in this nanostructure can be boosted by one order of magnitude with respect to the isolated nanodisk.
Lavinia Ghirardini, Valerio F. Gili, Davide Rocco, Giovanni Pellegrini, Luca Carletti, Lamberto Duò, Marco Finazzi, Andrea Locatelli, Ivan Favero, Giuseppe Leo, Aristide Lemaitre, Costantino De Angelis, and Michele Celebrano, "Engineering second-harmonic generation at the nanoscale using AlGaAs optical nanoantennas (Conference Presentation)," Proc. SPIE 10540, Quantum Sensing and Nano Electronics and Photonics XV, 105402C (Presented at SPIE OPTO: February 01, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2287092.5751523636001.
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