UC Irvine

Nonlinear light-matter interactions have been key to advances in biological imaging and sensing. Naturally, customized light fields have been deployed to draw out and target these nonlinear phenomenon. In the case of Surface Plasmon Polaritons, electro-magnetic fields are confined to a nearly two dimensional region on a supporting metallic thin film. Here we explore consequences and applications of using gold films to support these propagating surface modes. The presence of sub-$\mu$m-sized particles in the excitation area distorts and confines the surface field, resulting in nonlinear electron-hole pair generation in the gold followed by radiative recombination. This mechanism, in which the gold film is both the source of strong near-fields as well as the antenna for coupling radiation to the far-field, holds promise as a label-free sensing mechanism of small particles near the surface. In addition, the ability to simultaneously support multiple SPP fields with well defined momenta allows for an unconventional method of generating four-wave mixing signals at the film surface. SPP mediated coherent anti-Stokes Raman scatterig (CARS) signals from biological samples are demonstrated, revealing unconventional imaging properties.