Coherent Multiphoton Control of Gallium Phosphide Nanodisk Resonances

High-index dielectric nanoantennas have recently emerged as promising alternatives to plasmonic nanoantennas for concentrating and manipulating light at the nanoscale. For example, gallium phosphide (GaP) nanoantennas display extremely low losses in the visible range and high nonlinearities, support both electric and magnetic resonances, and are nicely compatible with CMOS fabrication technology. Especially, the low losses and large nonlinearities are promising for ultrafast optical switching and truly all-optical control of GaP nanodevices. Here first we use two- and three-photon excitation of GaP nanodisks to probe the size-dependent resonance enhancement of second-harmonic and bandgap emission. Next, we show, by spectral phase control of broadband pulsed excitation, that GaP nanoantennas outperform their metal counterparts in supporting nonlinear optical coherences.