Engineering nonlinear response of nanomaterials using Fano resonances

Abstract

We show that, nonlinear optical processes of nanoparticles can be controlled by the presence of interactions with a molecule or a quantum dot. By choosing the appropriate level spacing for the quantum emitter, one can either suppress or enhance the nonlinear frequency conversion. We reveal the underlying mechanism for this effect, which is already observed in recent experiments: (i) Suppression occurs simply because transparency induced by Fano resonance does not allow an excitation at the converted frequency. (ii) Enhancement emerges since nonlinear process can be brought to resonance. Path interference effect cancels the nonresonant frequency terms. We demonstrate the underlying physics using a simplified model, and we show that the predictions of the model are in good agreement with the 3-dimensional boundary element method (MNPBEM toolbox) simulations. Here, we consider the second harmonic generation in a plasmonic converter as an example to demonstrate the control mechanism. The phenomenon is the semi-classical analog of nonlinearity enhancement via electromagnetically induced transparency.

Fluorescence excitation by enhanced plasmon upconversion under continuous wave illumination

“…In our theoretical and numerical studies using 3D simulations with retardation effects [23,26,28,29], we have demonstrated that path interference schemes can be adopted to gain control over the nonlinear frequency conversion processes emerging in plasmonic resonators. By appropriately choosing the level spacing of the quantum oscillator (i.e.…”

“…In two recent theoretical works [26,28] 3D boundary element method (MNPBEM [31]) simulations demonstrate that second harmonic generation in plasmonic resonators can be enhanced by using the Fano resonances. In these simulations, the retardation effects are taken into account, where it is confirmed that the retardation effects do not play a significant role on the existence of SHG enhancement.…”

“…Such an enhancement occurs since the path interference effects cancel nonresonant terms [see Eq. (9) below] and bring the nonlinear conversion to resonance [26]. In the following part, we discuss the enhancement mechanism within the framework of Fano resonance.…”

“…(Radiative decay is weak for even plasmon modes.) Therefore, the Hamiltonian for the process can be written as [26] …”

“…Recent studies [26][27][28] reveal that Fano resonances of coupled plasmonic-quantum systems can also enhance the SHG and four-wave mixing [29] processes. In our theoretical and numerical studies using 3D simulations with retardation effects [23,26,28,29], we have demonstrated that path interference schemes can be adopted to gain control over the nonlinear frequency conversion processes emerging in plasmonic resonators.…”