We report on an experimental study of the optical properties
of a metal-molecular aggregate hybrid nanostructure
consisting of a gold nanoslit array coated with a
thin J-aggregated dye layer. Our experiments reveal a
strong coupling between the surface plasmon polaritons
(SPPs) excited on a nanoslit array and the aggregate
excitons with a large Rabi splitting energy (ΩR). Ultrafast
excitation drastically alters the optical response
of the hybrid nanostructure inducing transient switching
from the strong to weak the coupling regime due
to the bleaching of the exciton resonance. The externally
controlled switching is fully reversible and occurs
on sub-ps timescale. The results are explained within a
phenomenological two coupled oscillator model. Such a
strong interaction can, e.g., be used to fabricate ultrafast
all-optical plasmonic switches or tunable mirrors.

We consider the frequency- and angle-dependent reflectivity of hybrid structures
containing metallic components and an optically excitable medium such as organic dyes
or semiconductor quantum wells. Clear signatures of a coupling between surface plasmon
polaritons and excitons in the excitable medium, in particular avoided crossings with
hybridization gaps in the range ≈ 10-100 meV, are found both experimentally and theoretically.

We demonstrate an ultrafast manipulation of the Rabi splitting energy Ω_R in a metal-molecular
aggregate hybrid nanostructure. Femtosecond excitation drastically alters the optical properties of a model system formed by coating a gold nanoslit array with a thin J-aggregated dye layer. Controlled and reversible transient switching from strong (Ω_R ~ 55 meV) to weak (Ω_R ~ 0) coupling on a sub-ps time scale is directly evidenced by mapping the nonequilibrium dispersion relations of the coupled excitations. Such a strong, externally controllable coupling of excitons and surface plasmon polaritons is of considerable interest for ultrafast alloptical switching applications in nanoscale plasmonic circuits.

Ultra-fast nano-optics is a comparatively young and
rapidly growing field of research aiming at probing, manipulating
and controlling ultrafast optical excitations on nanometer
length scales. This ability to control light on nanometric length
and femtosecond time scales opens up exciting possibilities for
probing dynamic processes in nanostructures in real time and
space. This article gives a brief introduction into the emerging research
field of ultrafast nano-optics and discusses recent progress
made in it. A particular emphasis is laid on the recent experimental
work performed in the authors’ laboratories. We specifically
discuss how ultrafast nano-optical techniques can be used to
probe and manipulate coherent optical excitations in individual
and dipole-coupled pairs of quantum dots, probe the dynamics
of surface plasmon polariton excitations in metallic nanostructures,
generate novel nanometer-sized ultrafast light and electron
sources and reveal the dipole interaction between excitons
and surface plasmon polaritons in hybrid metal-semiconductor
nanostructures. Our results indicate that such hybrid nanostructures
carry significant potential for realizing novel nano-optical
devices such as ultrafast nano-optical switches as well as surface
plasmon polariton amplifiers and lasers.

We report on an experimental study of the optical properties of a metal-semiconductor hybrid structure consisting of a gold grating on a GaAs quantum well (QW). Our experiments reveal a coherent coupling between the surface plasmon polaritons (SPP) excited on a metal grating and the QW excitons. The hybrid structure is designed to optimize the radiative exciton-SPP interaction which is probed by low-temperature, angle-resolved far-field reflection spectroscopy. As a result of the coupling, a significant shift of sim7 meV and an increase in broadening by sim4 meV of the QW exciton resonance are observed. The results are explained with the help of a phenomenological two layered model, predicting coupling strengths as large as 30 meV. Such a strong interaction can, e.g. be used to enhance the luminescence yield of semiconductor quantum structures or to amplify SPP waves. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A thorough theoretical understanding of the interaction of excitons and surface plasmon polaritons (SPP) in metal-semiconductor hybrid structures is of fundamental importance for the design of SPP-based devices. A theory to describe SPP-exciton interaction in a periodic multilayer film system is presented and demonstrated. In a hybrid System of gold nanowires on top of a GaAs/AlGaAs quantum well (QW), our calculations shaw the formation of coupled SPP-exciton modes. These are predicted to be observable in reflection spectra and by near-field scanning optical microscopy.

We report measurements of a coherent coupling between surface plasmon polaritons (SPP) and
quantum well excitons in a hybrid metal-semiconductor nanostructure. The hybrid structure is designed
to optimize the radiative exciton-SPP interaction which is probed by low-temperature, angle-resolved, farfield
reflectivity spectroscopy. As a result of the coupling, a significant shift of ~7 meV and an increase in
broadening by ~4 meV of the quantum well exciton resonance are observed. The experiments are
corroborated by a phenomenological coupled-oscillator model predicting coupling strengths as large as
50 meV in structures with optimized detunings between the coupled exciton and SPP resonances. Such a
strong interaction can, e.g., be used to enhance the luminescence yield of semiconductor quantum
structures or to amplify SPP waves.

We have recently studied excitonic effects on the optical properties of single-walled carbon nanotubes by means of two-photon spectroscopy and time-resolved photoluminescence spectroscopy, For nanotubes with diameters between 6.8 angstrom and 9.0 angstrom, the two-photon spectra give evidence for large binding energies between 300 meV to 400 meV. Theoretical simulations of these spectra indicate that the lowest energy exciton state in nanotubes is an optically dark exciton, which has profound implications on the luminescence yield and exciton dynamics in single-walled nanotubes. Indeed, time-resolved photoluminescence measurements of individual nanotubes reveal low quantum yields and rather short exciton lifetimes ranging from 10 ps to 200 ps, which are affected by exciton relaxation between bright and dark states and non-radiative exciton recombination. These results suggest that a control of the radiative lifetime of nanotube excitons may be a viable strategy for enhancing their luminescence yield. Here, we propose that exciton coupling to surface plas-non polaritons in metallic nanostructures may result in a substantial enhancement of the radiative exciton decay rate, Two-photon luminescence excitation spectra of single-walled carbon nanotubes. The luminescence intensity is plotted as a function of excitation and detection wavelength. The various two-photon resonances are assigned to nanotube species with different chiral indices (n, m), as indicated in the figure.