The coupling of nanostructures with emitters opens up ways for the realization of man-made subwavelength light emitting elements. In this article we present an overview of our recent progress in the modification of fluorescence when an emitter is placed close to a nanostructure. In order to control the wealth of parameters that contribute to this process, we have combined scanning probe technology with single molecule microscopy and spectroscopy. We discuss the enhancement and reduction of molecular excitation and emission rates in the presence of a dielectric or metallic nanoparticle and emphasize the role of plasmon resonances in the latter. Furthermore, we examine the spectral and angular emission characteristics of the molecule-particle system. The experimental findings are in excellent semi-quantitative agreement with the outcome of theoretical calculations. We show that the interaction of an emitter with a nanoparticle can be expressed in the framework of an optical nanoantennae and propose arrangements that could lead to the modification of spontaneous emission by more than 1000 times.
Efficient coupling of photons to a single molecule and the observation of its resonance fluorescence
G. Wrigge,
I. Gerhardt,
J. Hwang,
G. Zumofen,
Vahid Sandoghdar
Single dye molecules at cryogenic temperatures exhibit many spectroscopic phenomena known from the study of free atoms and are thus promising candidates for experiments in fundamental quantum optics. However, the existing techniques for their detection have either sacrificed information on the coherence of the excited state or have been ineffcient. Here, we show that these problems can be addressed by focusing the excitation light near to the extinction cross-section of a molecule. Our detection scheme enables us to explore resonance fluorescence over nine orders of magnitude of excitation intensity and to separate its coherent and incoherent parts. In the strong excitation regime, we demonstrate the first direct observation of the Mollow fluorescence triplet from a single solid-state emitter. Under weak excitation, we report the detection of a single molecule with an incident power as faint as 600aW, paving the way for studying nonlinear effects with only a few photons.
Plasmon spectra of nanospheres under a tightly focused beam
Nassiredin M. Mojarad,
Vahid Sandoghdar,
Mario Agio
Journal of the Optical Society of America B-Optical Physics
25
651-658
(2008)
| Journal
We study the modification of the far-field cross sections and the near-field enhancement for gold and silver nanospheres illuminated by a tightly focused beam. Using a multipole-expansion approach we obtain an analytical solution to the scattering problem and provide insight on the effects of focusing on the optical response. Large differences with respect to Mie theory are especially found when the nanoparticle supports quadrupole or higher-order resonances. (C) 2008 Optical Society of America.
Coupling of plasmonic nanoparticles to their environments in the context of van der Waals-Casimir interactions
U. Hakanson,
M. Agio,
S. Kuehn,
L. Rogobete,
T. Kalkbrenner,
Vahid Sandoghdar
We present experiments in which the interaction of a single gold nanoparticle with glass substrates or with another gold particle can be tuned by in situ control of their separations using scanning probe technology. We record the plasmon resonances of the coupled systems as a function of the polarization of the incident field and the particle position. The distinct spectral changes of the scattered light from the particle pair are in good agreement with the outcome of finite-difference time-domain calculations. We believe that our experimental technique holds promise for the investigation of the van der Waals-Casimir-type interactions between nanoscopic neutral bodies.
Gold nanorods and nanospheroids for enhancing spontaneous emission
We compute the radiative decay rate and the quantum efficiency for an emitter coupled to gold nanorods and nanospheroids using the body-of-revolution finite-difference time-domain method. We study these quantities as a function of the nanoparticle aspect ratio and volume, showing that large enhancements can be achieved with realistic parameters. Moreover, we find that nanospheroids exhibit better performances than nanorods for applications in the visible and near-infrared spectral range.
Exploring the limits of single emitter detection in fluorescence and extinction
G. Wrigge,
J. Hwang,
I. Gerhardt,
G. Zumofen,
Vahid Sandoghdar
We present an experimental comparison and a theoretical analysis of the signal-to-noise ratios in fluorescence and extinction spectroscopy of a single emitter. We show that because of its homodyne nature the extinction measurements can be advantageous if the emitter is weakly excited. Furthermore, we discuss the potential of this method for the detection and spectroscopy of weakly emitting systems such as rare earth ions. (C) 2008 Optical Society of America
Perfect Reflection of Light by an Oscillating Dipole
G. Zumofen,
N. M. Mojarad,
Vahid Sandoghdar,
M. Agio
We show theoretically that a directional dipole wave can be perfectly reflected by a single pointlike oscillating dipole. Furthermore, we find that, in the case of a strongly focused plane wave, up to 85% of the incident light can be reflected by the dipole. Our results hold for the full spectrum of the electromagnetic interactions and have immediate implications for achieving strong coupling between a single propagating photon and a single quantum emitter.
Contact
Nano-Optics Division Prof. Vahid Sandoghdar
Max Planck Institute for the Science of Light Staudtstr. 2 91058 Erlangen, Germany
