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

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. \textit{(i)} A linear Fano resonance can enhance the hot spot field, resulting enhanced nonlinear signal. \textit{(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

Fano-control of down-conversion in a nonlinear crystal embedded with plasmonic-quantum emitter hybrid structures

Control of nonlinear response of nanostructures via path interference effects, i.e., Fano resonances, has been studied extensively. In such studies, a frequency conversion process takes place near a hot spot. Here, we study the case where the frequency conversion process takes place \textit{along the body of a nonlinear crystal}. Metal nanoparticle-quantum emitter dimers control the down-conversion process, taking place throughout the crystal body, via introducing interfering conversion paths. Dimers behave as interaction centers. We show that a 2 orders of magnitude enhancement is possible, on top of the enhancement due to localization effects. That is, this factor multiplies the enhancement taking place due to the field localization

Ultra-large actively tunable photonic band gaps via plasmon-analog of index enhancement

We present a novel method for active continuous-tuning of a band gap which has a great potential to revolutionize current photonic technologies. We study a periodic structure of x and y-aligned nanorod dimers. Refractive index of a y-polarized probe pulse can be continuously-tuned by the intensity of an x-polarized auxiliary (pump) pulse. Order of magnitude index-tuning can be achieved with a vanishing loss using the plasmon-analog of refractive index enhancement [Phys. Rev. B 100, 075427 (2019)]. Thus, a large band gap can be created from a non-existing gap via the auxiliary pulse. We also present a "proof of principle" demonstration of the phenomenon using numerical solutions of Maxwell equations. The new method, working for any crystal dimensions, can also be utilized as a linear photonic switch operating at tens of femtoseconds