328 research outputs found
Spontaneous radiative decay of translational levels of an atom near a dielectric surface
We study spontaneous radiative decay of translational levels of an atom in
the vicinity of a semi-infinite dielectric. We systematically derive the
microscopic dynamical equations for the spontaneous decay process. We calculate
analytically and numerically the radiative linewidths and the spontaneous
transition rates for the translational levels. The roles of the interference
between the emitted and reflected fields and of the transmission into the
evanescent modes are clearly identified. Our numerical calculations for the
silica--cesium interaction show that the radiative linewidths of the bound
excited levels with large enough but not too large vibrational quantum numbers
are moderately enhanced by the emission into the evanescent modes and those for
the deep bound levels are substantially reduced by the surface-induced red
shift of the transition frequency
Backaction in metasurface etalons
We consider the response of etalons created by a combination of a
conventional mirror and a metasurface, composed of a periodic lattice of metal
scatterers with a resonant response. This geometry has been used previously for
perfect absorption, in so-called Salisbury screens, and for hybridization of
localized plasmons with Fabry-Perot resonances. The particular aspect we
address is if one can assume an environment-independent reflectivity for the
metasurface when calculating the reflectivity of the composite system, as in a
standard Fabry-Perot analysis, or whether the fact that the metasurface
interacts with its own mirror image renormalizes its response. Using lattice
sum theory, we take into account all possible retarded dipole-dipole
interactions of scatterers in the metasurface amongst each other, and through
the mirror. We show that while a layer-by-layer Fabry-Perot formalism captures
the main qualitative features of metasurface etalons, in fact the mirror
modifies both the polarizability and reflectivity of the metasurface in a
fashion that is akin to Drexhage's modification of the radiative properties of
a single dipole.Comment: 10 pages, 5 figure
Strongly nonexponential time-resolved fluorescence of quantum-dot ensembles in three-dimensional photonic crystals
We observe experimentally that ensembles of quantum dots in three-dimensional (3D) photonic crystals reveal strongly nonexponential time-resolved emission. These complex emission decay curves are analyzed with a continuous distribution of decay rates. The log-normal distribution describes the decays well for all studied lattice parameters. The distribution width is identified with variations of the radiative emission rates of quantum dots with various positions and dipole orientations in the unit cell. We find a striking sixfold change of the width of the distribution by varying the lattice parameter. This interpretation qualitatively agrees with the calculations of the 3D projected local density of states. We therefore conclude that fluorescence decay of ensembles of quantum dots is highly nonexponential to an extent that is controlled by photonic crystals
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
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
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
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
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
Excitated state properties of 20-chloro-chlorophyll a
The excited-state and lasing properties of 20-chloro-chlorophyll a in ether solution were compared to those of chlorophyll a. Desactivation parameters and cross-sections were obtained from non-linear absorption spectroscopy in combination with a physico-mathematical methods package. The Cl substituent at C-20 (1) increases both intersystem crossing and internal conversion, (2) produces a blue-shift of the S1 absorption spectrum, and (3) leads to pronounced photochemistry
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
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