All-optical Control of Nonlinear Emissions in a Single Plasmonic Molecular Nanocavity

Project: Research

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Recent research attention has been focused on the use of plasmonic nanostructures to enhance the nonlinear frequency conversion efficiency of metals in sub-diffractionlimited volumes. For example, enhanced second- and third-harmonic generation (S/THG) of light has been demonstrated in a single plasmonic nanocavity consisting of a metal nanoparticle separated from a metal film by a nanometer-thick self-assembled molecular monolayer or a dielectric oxide layer. So far, the S/THG efficiency in such a plasmonic nanocavity can be controlled only in a passive manner, namely, through simply adjusting the particle-film gap distance by changing the molecular length or the oxide film thickness. Conversely, active control such as electrical, optical and electrochemical modulation of the nonlinear optical phenomena in plasmonic structures remains relatively unexplored. Realization of active control in nonlinear plasmonics is of essential importance for photonics applications, particularly for optical signal and information processing. Additionally, it remains unclear whether the particle-film contact area has a substantial effect on the nonlinear emission efficiency of the plasmonic nanocavity.The aim of the proposed research is to realize all-optical control of the nonlinear emissions in an individual plasmonic molecular nanocavity. The nanocavity consists of a single gold nanoparticle (nanosphere, nanorod, or nanocube) separated from a gold mirror by a self-assembled monolayer of photoactive molecules, a hybrid platform of metal nanophotonics and molecular electronics. Here the photoconductive path at the particle-film junction can be optically triggered in a fast and repeatable manner, leading to an all-optical modulation of the effective dielectric environment of the junction and so for the linear and nonlinear optical properties of the nanocavity. The all-optical control of the linear plasmonic response is expected to manifest itself by a significant blueshift in the bonding dipolar plasmon (BDP) resonance and possible appearance of a low-energy tunneling charge transfer plasmon (tCTP) resonance upon switching on the conductive path under ultraviolet-light illumination; The system will recover to its initial state upon silencing the conductive junction with visible-light illumination. Thus, by setting the fundamental femtosecond excitation wavelength at the BDP (tCTP) resonance, one can optically modulate the emission intensity of ultraviolet-visible SHG (THG) through plasmonic on- or off-resonance enhancement. The project will be carried out in collaboration with Prof. Peter Nordlander at Rice University (US), and his team will be responsible for theoretical understanding of the light-induced charge transfer across the conductive junction that serves as the physical mechanism for the plasmon resonance tuning of the nanocavity. 


Project number9042763
Grant typeGRF
Effective start/end date1/01/1827/06/22