Controlling steady-state second harmonic signal via linear and nonlinear Fano resonances

Abstract

Nonlinear signal even from a single molecule becomes visible at hot spots of plasmonic nanoparticles. In these structures, Fano resonances can control the nonlinear response in two ways. (i) A linear Fano resonance can enhance the hot spot field, resulting enhanced nonlinear signal. (ii) A nonlinear Fano resonance can enhance the nonlinear signal without enhancing the hot spot. In this study, we compare the enhancement of second harmonic signal at the steady-state obtained via these two methods. Since we are interested in the steady-state signal, we adapt a linear enhancement which works at the steady-state. This is different than the dark-hot resonances that appears in the transparency window due to enhanced plasmon lifetime.

Modulating the temporal dynamics of nonlinear ultrafast plasmon resonances

“…Decreasing the nanogap size between nanoparticles increases the intensity which in turn enhances the lifetime of the plasmonic field in contrast with the response of the field outside the nanogap. In the same way, the increase in electric field intensities of linear and nonlinear plasmon modes have been suggested through Fano resonance [20]. On the other hand, a recent study demonstrates that interacting nanostructures which support two different plasmon modes(bright and dark) can significantly alter the ultrafast response even in a very weak coupling regime [21].…”

“…The model systems consist of two interacting nanostructures analog to coupled harmonic oscillators with a weak coupling strength [20,23]. The combined plasmonic systems have coherent plasmon resonances with modified lifetimes.…”

Fano enhancement of second harmonic field via dark-bright plasmon coupling

“…Enhancement, due to path interference effects, of both linear [22] and nonlinear [23] phenomena that emerged from the hot spots of plasmonic structures, is well studied via coupling plasmonic modes to the two-level quantum structures. These path interference effects (Fano resonances), besides the emitter-plasmon coupling, can also appear when the plasmon mode of the metal nanoparticle is coupled to a long-live dark plasmon mode [24].…”

“…In this paper, we utilize bright-dark plasmon coupling in which to gain control over both the linear and the nonlinear field intensity. Different from our previous work [23], here, we consider both linear and nonlinear Fano resonances at the same setup by coupling two distinct plasmonic dark modes to the plasmonic structure having second harmonic generation property, as shown in Figure 1. It is known that enhancement of the second harmonic field can be observed by enhancing the first harmonic mode resulting in the enhanced second-harmonic field (linear Fano resonance) or coupling the emitter to the second harmonic mode (nonlinear Fano resonance) to enhance the second harmonic field without modifying the first harmonic field [23].…”

“…Different from our previous work [23], here, we consider both linear and nonlinear Fano resonances at the same setup by coupling two distinct plasmonic dark modes to the plasmonic structure having second harmonic generation property, as shown in Figure 1. It is known that enhancement of the second harmonic field can be observed by enhancing the first harmonic mode resulting in the enhanced second-harmonic field (linear Fano resonance) or coupling the emitter to the second harmonic mode (nonlinear Fano resonance) to enhance the second harmonic field without modifying the first harmonic field [23]. The existence of the second long-live mode, as studied here, can be useful to enhance one of the modes by suppressing the other or to obtain the better enhancement of the nonlinear field intensity by applying both enhancement schemes at the same time.…”