Second Harmonic Generation from Three-Fold Non-Centrosymmetric Gold Nanostructures

Francois Lagugne-Labarthet Department of Chemistry, Western University, London, Canada Renjie Hou Department of Chemistry, Western University, London, Canada Vasyl Shynkar Laboratoire Photonique Quantique et Moleculaire, Ecole Normale Superieure de Cachan, Cachan, France Joseph Zyss Laboratoire Photonique Quantique et Moleculaire, Ecole Normale Superieure de Cachan, Cachan, France

In the past two decades, metallic nanostructures have been developed for a variety of applications such as in optical data storage, biosensing, or in high sensitivity spectroscopy aiming at probing single molecules.

Among all variety of optical properties driven by the size and the geometry of the metallic structures, the nonlinear optical properties observed under excitation with pulsed high peak-intensity laser can be strongly enhanced due to the confinement of the electromagnetic field impinging these metallic structures. Second or higher harmonic signals are detectable only if the input electric field is large enough which is accessible with short pulse lasers. The short pulses in the ns to fs range yield local field in the GW/cm2 range, driving the oscillation of the electrons of the metal in a non-linear way.

In second harmonic generation (SHG) the signal is observable when the material or molecules are arranged in a non-centrosymmetric fashion, i.e. when the structures do not present an inversion center. SHG can be therefore optimized by tuning the symmetry of the system (molecule, crystal, metastructure) and subsequently by manipulating the send order susceptibility elements intrinsic to the material or the structure. In this context, advanced nanofabrication technology allows one to conceive meta-materials with no center of symmetry in order to optimize SHG properties through the tuning of χ(2), the second order nonlinear susceptibiity.

In this presentation, we focus on second harmonic generation of 2D non-centrosymmetric gold structures. A strong enhancement of SHG signal from the nano-structures is observed when the wavelength of the fundamental excitaton is within in the extinction band of the nanostructure. By controlling the gap distance between adjacent gold nanostructures, a plasmon-mediated optical coupling can be controlled. SHG polarized measurements performed under microscopy conditions are correlated with electromagnetic field modeling to evaluate such optical coupling effects.

Salomon, A.; Zielinski, M.; Kolkowski, R.; Zyss, J.; Prior, Y., “Size and Shape Resonances in Second Harmonic Generation from Silver Nanocavities.” J Phys Chem C 2013, 117, 22377-22382.

flagugne@uwo.ca









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