606 research outputs found
Statistical properties of spontaneous emission near a rough surface
We study the lifetime of the excited state of an atom or molecule near a
plane surface with a given random surface roughness. In particular, we discuss
the impact of the scattering of surface modes within the rough surface. Our
study is completed by considering the lateral correlation length of the decay
rate and the variance discussing its relation to the C0 correlation
Photonic mode density effects on single-molecule fluorescence blinking
We investigated the influence of the photonic mode density (PMD) on the
triplet dynamics of individual chromophores on a dielectric interface by
comparing their response in the presence and absence of a nearby gold film.
Lifetimes of the excited singlet state were evaluated in ordet to measure
directly the PMD at the molecules position. Triplet state lifetimes were
simultaneously determined by statistical analysis of the detection time of the
fluorescence photons. The observed singlet decay rates are in agreement with
the predicted PMD for molecules with different orientations. The triplet decay
rate is modified in a fashion correlated to the singlet decay rate. These
results show that PMD engineering can lead to an important suppression of the
fluorescence, introducing a novel aspect of the physical mechanism to enhance
fluorescence intensity in PMD-enhancing systems such as plasmonic devices
Size-Dependence of the Wavefunction of Self-Assembled Quantum Dots
The radiative and non-radiative decay rates of InAs quantum dots are measured
by controlling the local density of optical states near an interface. From
time-resolved measurements we extract the oscillator strength and the quantum
efficiency and their dependence on emission energy. From our results and a
theoretical model we determine the striking dependence of the overlap of the
electron and hole wavefunctions on the quantum dot size. We conclude that the
optical quality is best for large quantum dots, which is important in order to
optimally tailor quantum dot emitters for, e.g., quantum electrodynamics
experiments.Comment: 5 pages, 3 figure
Measuring the quantum efficiency of single radiating dipoles using a scanning mirror
Using scanning probe techniques, we show the controlled manipulation of the
radiation from single dipoles. In one experiment we study the modification of
the fluorescence lifetime of a single molecular dipole in front of a movable
silver mirror. A second experiment demonstrates the changing plasmon spectrum
of a gold nanoparticle in front of a dielectric mirror. Comparison of our data
with theoretical models allows determination of the quantum efficiency of each
radiating dipole.Comment: 4 pages, 4 figure
Metallo-dielectric hybrid antennas for ultrastrong enhancement of spontaneous emission
We devise new optical antennas that reduce the excited-state radiative
lifetimes of emitters to the order of 100 femtoseconds while maintaining
quantum efficiencies of about 80% at a broadband operation. Here, we combine
metallic nanoparticles with planar dielectric structures and exploit design
strategies from plasmonic nanoantennas and concepts from Cavity Quantum
Electrodynamics to maximize the local density of states and minimize the
nonradiative losses incurred by the metallic constituents. The proposed
metallo-dielectric hybrid antennas promise important impact on various
fundamental and applied research fields, including photophysics, ultrafast
plasmonics, bright single photon sources and Raman spectroscopy
Observation of modified radiative properties of cold atoms in vacuum near a dielectric surface
We have observed a distance-dependent absorption linewidth of cold Rb
atoms close to a dielectric-vacuum interface. This is the first observation of
modified radiative properties in vacuum near a dielectric surface. A cloud of
cold atoms was created using a magneto-optical trap (MOT) and optical molasses
cooling. Evanescent waves (EW) were used to observe the behavior of the atoms
near the surface. We observed an increase of the absorption linewidth with up
to 25% with respect to the free-space value. Approximately half the broadening
can be explained by cavity-quantum electrodynamics (CQED) as an increase of the
natural linewidth and inhomogeneous broadening. The remainder we attribute to
local Stark shifts near the surface. By varying the characteristic EW length we
have observed a distance dependence characteristic for CQED.Comment: 6 pages, 6 figures, some minor revision
Strongly Coupled Matter-Field and Non-Analytic Decay Rate of Dipole Molecules in a Waveguide
The decay rate \gam of an excited dipole molecule inside a waveguide is
evaluated for the strongly coupled matter-field case near a cutoff frequency
\ome_c without using perturbation analysis. Due to the singularity in the
density of photon states at the cutoff frequency, we find that \gam depends
non-analytically on the coupling constant as . In contrast
to the ordinary evaluation of \gam which relies on the Fermi golden rule
(itself based on perturbation analysis), \gam has an upper bound and does not
diverge at \ome_c even if we assume perfect conductance in the waveguide
walls. As a result, again in contrast to the statement found in the literature,
the speed of emitted light from the molecule does not vanish at \ome_c and is
proportional to which is on the order of m/s for
typical dipole molecules.Comment: 4 pages, 2 figure
A multiple-scattering approach to interatomic interactions and superradiance in inhomogeneous dielectrics
The dynamics of a collection of resonant atoms embedded inside an
inhomogeneous nondispersive and lossless dielectric is described with a dipole
Hamiltonian that is based on a canonical quantization theory. The dielectric is
described macroscopically by a position-dependent dielectric function and the
atoms as microscopic harmonic oscillators. We identify and discuss the role of
several types of Green tensors that describe the spatio-temporal propagation of
field operators. After integrating out the atomic degrees of freedom, a
multiple-scattering formalism emerges in which an exact Lippmann-Schwinger
equation for the electric field operator plays a central role. The equation
describes atoms as point sources and point scatterers for light. First,
single-atom properties are calculated such as position-dependent
spontaneous-emission rates as well as differential cross sections for elastic
scattering and for resonance fluorescence. Secondly, multi-atom processes are
studied. It is shown that the medium modifies both the resonant and the static
parts of the dipole-dipole interactions. These interatomic interactions may
cause the atoms to scatter and emit light cooperatively. Unlike in free space,
differences in position-dependent emission rates and radiative line shifts
influence cooperative decay in the dielectric. As a generic example, it is
shown that near a partially reflecting plane there is a sharp transition from
two-atom superradiance to single-atom emission as the atomic positions are
varied.Comment: 18 pages, 4 figures, to appear in Physical Review
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