Enhanced Third-Harmonic Generation in Silicon Nanoparticles Driven by Magnetic Response

We observe enhanced third-harmonic
generation from silicon nanodisks
exhibiting both electric and magnetic dipolar resonances. Experimental
characterization of the nonlinear optical response through third-harmonic
microscopy and spectroscopy reveals that the third-harmonic generation
is significantly enhanced in the vicinity of the magnetic dipole resonances.
The field localization at the magnetic resonance results in two orders
of magnitude enhancement of the harmonic intensity with respect to
unstructured bulk silicon with the conversion efficiency limited only
by the two-photon absorption in the substrate.