Frequency Tripling via Sum-Frequency Generation at the Nanoscale

High refractive index dielectric nanostructures can be exploited to enhance nonlinear optical processes via the strong light confinement by their resonant modes. The sensitive dependence of these modes on the geometry and material composition offers ample opportunities for tailoring the optical response of the system. Here we report sum-frequency generation (SFG) by individual AlGaAs nanocylinders, pumped by two pulsed beams at a telecommunication frequency, ω, and its duplicate, 2ω. Under such a scheme, the SFG at 3ω = ω + 2ω is degenerate with the third-harmonic generation (THG) seeded by the input at ω, thereby tripling its frequency via the second-order permittivity χ(2), rather than via χ(3) as in THG. The concurrent detection of THG and SFG enables us to determine χ(3) = 7 × 10-20 m2/V2 by comparing experiments to numerical simulations and based on the known value of χ(2). We observe a rich size- and polarization-dependent behavior that gives appeal to the studied system as a key component of miniaturized photonic devices.