Nanoparticle Acoustic Resonance Enhanced Nearly Degenerate Four-Wave Mixing

Nanoparticles have acoustic resonances in the 10 GHz to THz range, which makes them interesting for resonantly enhanced four-wave mixing applications such as frequency conversion. Using a nearly degenerate four-wave mixing setup and comparing with Rayleigh Gans Debye scattering, we estimate a nonlinear refractive index, n, of approximately 2 x 10(-5) cm(2)/MW for 22 nm polystyrene nanospheres in water at a difference frequency of 43 GHz. This is nearly 3 orders of magnitude larger than the typical below-band-gap nonlinear response of semiconductors. This strong high-frequency response may be ideal for four-wave conversion in all-optical information technologies, with appropriately chosen nanoparticle sizes.