Harmonic generation from silicon membranes at visible and ultraviolet wavelengths.

Nonlinear silicon photonics offers unique abilities to generate, manipulate and detect optical signals in nano-devices, with applications based on field localization and large third order nonlinearity. However, at the nanoscale, inefficient nonlinear processes, absorption, and the lack of realistic models limit the nano-engineering of silicon. Here we report measurements of second and third harmonic generation from undoped silicon membranes.

Harmonic generation from gold nanolayers: bound and hot electron contributions to nonlinear dispersion.

Understanding how light interacts with matter at the nanoscale is pivotal if one is to properly engineer nano-antennas, filters and other devices whose geometrical features approach atomic size. We report experimental results on second and third harmonic generation from 20 nm- and 70 nm-thick gold layers, for TE- and TM-polarized incident light pulses. We discuss the relative roles that bound electrons and an intensity dependent free electron density (hot electrons) play in third harmonic generation.

Directional Ultrasound Source for Solid Materials Inspection: Diffraction Management in a Metallic Phononic Crystal.

In this work, we numerically investigate the diffraction management of longitudinal elastic waves propagating in a two-dimensional metallic phononic crystal. We demonstrate that this structure acts as an "ultrasonic lens", providing self-collimation or focusing effect at a certain distance from the crystal output. We implement this directional propagation in the design of a coupling device capable to control the directivity or focusing of ultrasonic waves propagation inside a target object.

Single-shot d-scan technique for ultrashort laser pulse characterization using transverse second-harmonic generation in random nonlinear crystals.

We demonstrate a novel dispersion-scan (d-scan) scheme for single-shot temporal characterization of ultrashort laser pulses. The novelty of this method relies on the use of a highly dispersive crystal featuring antiparallel nonlinear domains with a random distribution and size. This crystal, capable of generating a transverse second-harmonic signal, acts simultaneously as the dispersive element and the nonlinear medium of the d-scan device.

Harmonic generation in the opaque region of GaAs: the role of the surface and magnetic nonlinearities.

Phase-locked second and third harmonic generation in the opaque region of a GaAs wafer is experimentally observed and analyzed both in transmission and reflection. These harmonic components, which are generated close to the surface, can propagate through an opaque material as long as the pump is tuned to a region of transparency or semitransparency and correspond to the inhomogeneous solutions of Maxwell's equations with nonlinear polarization sources. We show that measurement of the angular and polarization dependence of the observed harmonic components allows one to infer the different nonlinear mechanisms that trigger these processes, including not only the bulk nonlinearity but also the surface and magnetic Lorentz contributions, which usually are either hidden by the bulk contributions or assumed to be negligible.