Show Abstract +
Currently, nanostructures are routinely fabricated and integrated in different photonic devices for a variety of purposes and applications. For instance, in order to engineer properly nano-antennas or filters, it is important to understand accurately how light interacts with metals, semiconductors, or ordinary dielectrics at the nanoscale. When the nanoscale is reached, light-matter interactions can display new phenomena, conventional approximations may not always be applicable, and new strategies must be sought in order to study and understand light-matter interactions at the nanoscale. Some examples of nanoscale optical phenomena are nonlocal effects, electronic wave function spill-out, discontinuous surface charge densities at metal-metal and metal-conducting oxide interfaces, and quantum tunneling, to name a few.
In this work, we present the study of two well-known nonlinear processes at the nanoscale, which are second and third harmonic generation. We report experimental results on second and third harmonic generation from 20nm- and 70nm-thick gold nanolayers, for TE- and TM-polarized incident light pulses. These measurements are compared with numerical simulations based on a microscopic hydrodynamic model which accounts for surface, magnetic and bulk nonlinearities arising from both free and bound charges, preserving linear and nonlinear dispersion, nonlocal effects due to pressure and viscosity, and an intensity dependent free electron density, to which we refer as hot electrons contribution.
We also discuss and highlight the relative roles bound electrons and hot electrons play in third harmonic generation. While planar structures are generally the simplest to fabricate, metal layers that are only a few nanometers thick and partially transparent are almost never studied. Yet, they offer an additional reference point for comparison, i.e. transmission, which through relatively simple experimental measurements affords the opportunity to test the accuracy of available theoretical models at the nanoscale.