Ultrafast Nonlinear Plasmonics

The mechanisms at the origin of the ultrafast third-order optical nonlinearity of metallic and plasmonic materials are described focusing on the dominant resonant processes associated to energy absorption. Optical nonlinearity is discussed in terms of ultrafast modifications of the dielectric function of the constituting metal as a consequence of electron and lattice heating, using a bulk-like model. Based on this description, the time- and spectral-dependent nonlinear changes of the optical response of plasmonic materials due to interaction with a femtosecond light pulse are modeled. The results are illustrated in the case of an individual gold nanoparticle for different shapes (sphere, ellipsoid, and rod), and for an ensemble of gold nanoparticles dispersed in a dielectric matrix. The same approach can be extended to more complex plasmonic materials or meta-materials.