Trade-Off between Second- and Third-Order Nonlinearities, Ultrafast Free Carrier Absorption and Material Damage inSilicon Nanoparticles

摘要

Reaching the optimal second- and third-order nonlinear conversion efficiencieswhile avoiding undesirable free carrier absorption losses and materialdamage in ultrashort laser-excited nanostructures is a challenging obstaclein all-dielectric ultrafast nanophotonics. In order to elucidate the mainaspects of this problem, a multi-physical model is developed, couplingnonlinear Maxwell equations supplied by surface and bulk nonlinearitieswith free carrier hydrodynamic equations for electron–hole plasma kineticsand electron-ion transfer for silicon. The maximum feasible efficiencies fora single spherical particle supporting different electric and magnetic resonancesare compared, and the harmonic yields are further optimized bytuning lattice resonances in a periodic arrangement of nanoparticles. Resultssupport the dominant role of magnetic dipole and quadrupole contributionsin the enhancement of the third harmonic and the electric dipole for thesecond harmonic, as well as the possibility to further improve the conversionof both harmonics simultaneously at least by two orders of magnitudeby designing properly the resonant metasurface.