Exploring the Optical Nonlinearities of Plasmon-Exciton Hybrid Resonances in Coupled Colloidal Nanostructures

Abstract

Strong coupling of plasmons and excitons can form hybrid states, the so-called "plexcitons". Although plasmons have a low quality factor, the exceptionally high coupling strength with molecular aggregates, in particular Jaggregates, allows the realization of strong interaction. Despite several studies in recent years showing the formation of plexcitonic states, their nature, especially at very short times, is still insufficiently investigated. In this article, we identify the nonlinear optical behavior of plexcitons formed on gold nanorods coated with J-aggregated cyanine molecules at short times by transient absorption spectroscopy and a simple Lorentz oscillator model. We control the spectral overlap of the two resonances and analyze the effect of detuning as well as the effect of off-and on resonance excitation on the hybrid states. We demonstrate that at ultrashort time scales plexcitons show tunable plasmonic and excitonic nonlinear performance according to the hybridization model. In a first approach, we discover a way to optically manipulate the quality factor and study the effects on the coupled hybrid states. As a second approach, we find that the coupling strength can also be influenced on an ultrashort time scale in the strong coupling regime when plexcitons are excited.

Optical Non-linearities in Plasmon-Exciton Core-Shell Particles: the Role of Heat

“…To further strengthen the hypothesis of a purely thermal origin of the transient signal as suspected in literature, 11,12 we additionally investigated the temporal behaviour for pump powers of 1 mW, 3 mW and 4.5 mW. We can safely assume that the energy deposited inside a particle ∆Q is proportional to the pump power.…”

“…Therefore, a higher damping of the resonances caused by particle heating has been proposed to be the source of the signal change also at the polariton resonances. 11,12 To calculate the influence of the transient heating, we inserted time dependent temperatures, obtained from the two-temperature model, into the simulation of the gold permittivity. This permittivity is then used in the Mie-Gans model.…”

“…Several studies have discussed the transient behaviour of coupled plasmonexciton systems on a time for scale beyond the polariton life time. [11][12][13] The main source for changes in the transient spectra at the polariton resonances was argued to be heat in the metal cores. But the arguments were rather phenomenological than rigid.…”

Induced Transparency in Plasmon–Exciton Nanostructures for Sensing Applications

“…Also, because of their high oscillator strength, caused by the delocalized nature of the excitonic excitations, especially attractive are also so‐called J‐aggregates of cyanine dyes . The most representative examples of this type of absorbers are TDBC (5,6‐dichloro‐2[3‐[5,6‐dichloro‐1‐ethyl‐3‐(3‐sulfopropyl)‐2(3H)‐benzimidazolidene]‐1‐propenyl]‐1‐ethyl‐3‐(3‐sulfopropyl) benzimidazolium hydroxide), JC‐1 (5,5′,6,6′‐tetrachloro‐1,1′,3,3′‐tetraethylbenzimidazolcarbo‐cyanine iodide), and PIC (1,1′‐diethyl‐2,2′‐cyanine iodide) to mention only a few.…”

Strong coupling effects in hybrid plexitonic systems

“…While observation of Rabi splitting in extinction or transmission spectra of exciton-plasmon (plexiton) hybrid systems has been reported in a number of publications 4 , photoluminescence (PL) properties of these systems in the strong coupling regime are more elusive to experimental investigation 4,5 . Also despite several studies in recent years showing the formation of plexcitonic states, their nature, especially at very short times, is still insufficiently investigated 6 . Finally, nothing is known to date about magneto-optical properties of hybrid plexitonic systems in strong coupling regime.…”