Nonlinearly coupled localized plasmon resonances: Resonant second-harmonic generation

Abstract

The efficient resonant nonlinear coupling between localized surface plasmon modes is demonstrated in a simple and intuitive way using boundary integral formulation and utilizing second-order optical nonlinearity. The nonlinearity is derived from the hydrodynamic description of electron plasma and originates from the presence of material interfaces in the case of small metal particles. The coupling between fundamental and second-harmonic modes is shown to be symmetry selective and proportional to the spatial overlap between polarization dipole density of the second-harmonic mode and the square of the polarization charge density of the fundamental mode. Particles with high geometrical symmetry will convert a far-field illumination into dark nonradiating second-harmonic modes, such as quadrupoles. Effective second-harmonic susceptibilities are proportional to the surface-to-volume ratio of a particle, emphasizing the nanoscale enhancement of the effect.

Fluorescence excitation by enhanced plasmon upconversion under continuous wave illumination

“…6, on the 12 nm AuNP possible. This is the mode in which SH conversion (532 nm oscillations) can take place due to the selection rules for the SHG process [9,10].…”

“…An efficient second harmonic (SH) active plasmonic metal nanostructure can be constructed by composing a cluster of colloidal metal nanoparticles with two different sizes [8]. It is of essence to break the centro-symmetry of the cluster in order to have a nonvanishing second order susceptibility, χ (2) [9,10]. The strategy in this approach is to minimize the volume of nonlinear photoactivation by selectively activating the single or probably a few molecules which is/are located in the vicinity of the gap between the nanoparticles of such an asymmetric cluster.…”

“…Presence of this quadrupole mode is very important for the emergence of the frequency conversion. Because the overlap integral for the SHG process possesses symmetry selection rules [9,10], see Eq. (2) and discussion below.…”

All-optical control of unipolar pulse generation in a resonant medium with nonlinear field coupling

“…(1). Such nonlinear field coupling can be expected, for instance, for nonlinearity coupled localized plasmonic resonances in the metallic nanostructures [47,48], hybrid aggregates of organic supramolecular assemblies and inorganic nanocrystals [49,50], coupled semiconductor microcavities [51], double quantum dot heterostructures [52,53] or other hybrid optical materials. The natural examples of such field coupling include also Raman-active media [54,55].…”

Resonant meta-atoms with nonlinearities on demand

“…Various configurations in both optical and radio-frequency (RF) domains were proposed, demonstrating dramatically improved nonlinear responses of the hybrid systems (see review 5 ). Nonlinearconversion efficiencies may be further improved by employing doubly resonant structures, which concentrate near fields at both the fundamental and multiple (nonlinear) frequencies 6,7,8,9 . This cascaded enhancement is based on recycling both the pump and the nonlinear fields in a cavity, where the latter may also originate from spontaneous vacuum fluctuations 10 .…”