Second harmonic generation from an individual all-dielectric nanoparticle: resonance enhancement versus particle geometry

Abstract

Nonlinear optical (NLO) nanostructures have played important roles in frequency conversion, optical switching, information storage and biomedical imaging. Although previous designs have focused on photonic crystals and metal plasmonic nanostructures, complex structure, large ohmic loss and Joule heating greatly hinder their practical applications. Beyond photonic crystals and metal plasmonic nanostructures, all-dielectric materials (ADMs) bring new ways to generate NLO behavior at subwavelength scales. We, for the first time to our knowledge, demonstrate irregular-geometry induced second harmonic generation (SHG) enhancement from an individual all-dielectric SiC nanoparticle. SHG conversion efficiency of single irregular-geometry SiC nanoparticles increases to 10⁻⁵ under an average excitation power of 6 mW at 880 nm excitation, thirtyfold higher than that of SiC nanosphere. We also establish that not only electric dipole mode but also magnetic dipole mode can exist in the vicinity of nanoparticles in mid-refractive (2 < n < 3) ADMs, and the stronger enhancement of the magnetic response induced by the irregular-geometry makes a great contribution to the SHG enhancement. A modified formula that includes electric and magnetic contributions is proposed to predict the SHG enhancement from ADMs. This discovery makes geometry-tuning all-dielectric nanoparticles promising in NLO nanostructures of nanophotonics in the future.