Nonlinear frequency conversion in strategic materials for nanophotonics

This project aims to contribute to two important research areas in Photonics: nonlinear optics and sub-wavelength nano-structured optical materials (nanomaterials). These inter-connected fields have major applications in the development of photonic devices at the nanoscale(NanoPhotonics). Nowadays nanomaterials are produced and integrated into an important number of devices and applications of Photonics. At nanometric scale, new phenomena arise and new strategies must be sought in order to understand and develop methods to harness the performance of deeply sub-wavelength optical materials having geometrical features that are a few atomic diameters in size. Nonlinear Optics (NLO) covers different processes, such as parametric frequency conversion, nonlinear scattering, ultrashort pulse generation, and characterization and sensing, to name a few. Traditionally, most efforts have been focused on the study of efficient harmonic generation in phase-matching (momentum conservation) conditions in thick materials having large nonlinearities (NL), when the harmonic generation is dominated by the electric dipole (?bulk?) contribution to the polarization density of the materials. However, when the material size is reduced to the nanoscale, the efficiency of the bulk contribution is drastically reduced or even vanish and other nonlinear contributions, arising from electric quadrupole or magnetic dipole interactions, become important and must be considered. For instance, in centrosymmetric materials like metals or Si, the bulk quadratic nonlinearity vanishes so that other nonlinear sources become essential to explain NL effects, such as surface harmonic generation. The presence of these terms can account for NL conversion in different situations traditionally considered as hostile environments for a harmonic generation. The experimental detection of very weak harmonic signal generated at the nanoscale is essential to obtain unique and unprecedented information in surface charact