Optical Stark Effects in $J$-Aggregate–Metal Hybrid Nanostructures Exhibiting a Strong Exciton–Surface-Plasmon-Polariton Interaction

We report on the observation of optical Stark effects in $J$-aggregate–metal hybrid nanostructures exhibiting strong exciton-surface-plasmon-polariton coupling. For redshifted nonresonant excitation, pump-probe spectra show short-lived dispersive line shapes of the exciton-surface-plasmon-polariton coupled modes caused by a pump-induced Stark shift of the polariton resonances. For larger coupling strengths, the sign of the Stark shift is reversed by a transient reduction in normal mode splitting. Our studies demonstrate an approach to coherently control and largely enhance optical Stark effects in strongly coupled hybrid systems. This may be useful for applications in ultrafast all-optical switching.

Figure 1

(a) Schematic of the two-color pump-probe experiment performed on a $J$-aggregated dye layer. Narrow-band, 60 fs duration pump pulses at 1.75 eV nonresonantly excite the $J$-aggregate exciton transition ($X$) at 1.79 eV. A broadband probe-pulse monitors the dynamics. The OSE results in a transient blueshift $\mathrm{\Delta }V(t)$ of the $X$ transition. (b) The differential reflectivity map $\mathrm{\Delta }R/R({\omega }_{\text{pr}},\tau )$ shows a short-lived, asymmetric dispersive line shape at the $X$ resonance arising from the interplay between the OSE and saturation of absorption. Dashed lines mark the maxima in $\mathrm{\Delta }R/R(\tau )$. (c) Experimental (symbols) and simulated (line) linear (top) and zero-delay $\mathrm{\Delta }R/R$ (bottom) spectra. (d) Top: Stark shift $\mathrm{\Delta }V$ dynamics (left) deduced from the experimental $\mathrm{\Delta }R/R(\tau )$ (right). Bottom: simulated pump-induced $X$ and biexciton ($XX$) population dynamics.

Figure 2

(a) Schematic of the pump-probe experiment performed on a $J$-aggregate–metal nanostructure exhibiting strong $X$-SPP coupling. (b) $\mathrm{\Delta }R/R(\tau ,{\omega }_{\text{pr}})$ map of a $J$-aggregate–metal hybrid structure with ${\mathrm{\Omega }}_{\mathrm{NMS}}=60\mathrm{meV}$ recorded at $\theta =29°$, near the anticrossing. Dashed lines mark the maxima in $\mathrm{\Delta }R/R(\tau )$. For pump pulses at 1.75 eV, the map shows a short-lived dispersive signal at the UP resonance (1.85–2.0 eV). (c) Experimental (symbols) and simulated (line) $\mathrm{\Delta }R/R$ spectra at selected delays. (d) Top: Stark shift $\mathrm{\Delta }{V}_{\mathrm{UP}}$ dynamics (left) and $\mathrm{\Delta }R/R(\tau )$ (right) at the UP resonance. Bottom: calculated pump-induced $X$ and SPP population dynamics.

Figure 3

(a) $\mathrm{\Delta }R/R(\tau ,{\omega }_{\text{pr}})$ map of a $J$-aggregate–metal hybrid nanostructure with ${\mathrm{\Omega }}_{\mathrm{NMS}}=110\mathrm{meV}$ measured at $\theta =22°$, detuned from the anticrossing. The transient dispersive signal at the UP (1.9–2.1 eV) shows a sign reversal with respect to that in Fig. 2. (b) Experimental (solid lines) $\mathrm{\Delta }R/R$ spectra ($\tau =0$) at two angles. The simulated spectrum (dashed line) at $\theta =22°$ is also shown. (c) Simulated $\mathrm{\Delta }R/R(\tau ,{\omega }_{\text{pr}})$ map including the effects of a time-dependent normal mode splitting ${\mathrm{\Omega }}_{\mathrm{NMS}}^{\prime }(t)$. Dashed lines mark the maxima in $\mathrm{\Delta }R/R(\tau )$. (d) Top: experimental $\mathrm{\Delta }R/R(\tau )$ at selected probe frequencies. Bottom: simulated pump-induced $X$ and SPP population dynamics at $\theta =22°$. ${\mathrm{\Omega }}_{\mathrm{NMS}}^{\prime }(t)$ is also depicted (dashed line).