860 research outputs found
Spatial coherence of thermal near fields
We analyze the spatial coherence of the electromagnetic field emitted by a
half-space at temperature T close to the interface. An asymptotic analysis
allows to identify three different contributions to the cross-spectral density
tensor in the near-field regime. It is shown that the coherence length can be
either much larger or much shorter than the wavelength depending on the
dominant contribution.Comment: 13 pages, 8 graphs, includes Elsevier elsart.cls preprint style.
Submitted to Optics Communications (27 july 2000
A mesoscopic description of radiative heat transfer at the nanoscale
We present a formulation of the nanoscale radiative heat transfer (RHT) using
concepts of mesoscopic physics. We introduce the analog of the Sharvin
conductance using the quantum of thermal conductance. The formalism provides a
convenient framework to analyse the physics of RHT at the nanoscale. Finally,
we propose a RHT experiment in the regime of quantized conductance
Quantum theory of spontaneous and stimulated emission of surface plasmons
We introduce a quantization scheme that can be applied to surface waves
propagating along a plane interface. An important result is the derivation of
the energy of the surface wave for dispersive non-lossy media without invoking
any specific model for the dielectric constant. Working in Coulomb's gauge, we
use a modal representation of the fields. Each mode can be associated with a
quantum harmonic oscillator. We have applied the formalism to derive
quantum-mechanically the spontaneous emission rate of surface plasmon by a
two-level system. The result is in very good agreement with Green's tensor
approach in the non-lossy case. Green's approach allows also to account for
losses, so that the limitations of a quantum approach of surface plasmons are
clearly defined. Finally, the issue of stimulated versus spontaneous emission
has been addressed. Because of the increasing density of states near the
asymptote of the dispersion relation, it is quantitatively shown that the
stimulated emission probability is too small to obtain gain in this frequency
region.Comment: 14 pages, 5 figures, submitted to Phys. Rev. B
Light scattering from cold rolled aluminum surfaces
We present experimental light scattering measurements from aluminum surfaces
obtained by cold rolling. We show that our results are consistent with a scale
invariant description of the roughness of these surfaces. The roughness
parameters that we obtain from the light scattering experiment are consistent
with those obtained from Atomic Force Microscopy measurements
A surface-scattering model satisfying energy conservation and reciprocity
In order for surface scattering models to be accurate they must necessarily
satisfy energy conservation and reciprocity principles. Roughness scattering
models based on Kirchoff's approximation or perturbation theory do not satisfy
these criteria in all frequency ranges. Here we present a surface scattering
model based on analysis of scattering from a layer of particles on top of a
substrate in the dipole approximation which satisfies both energy conservation
and reciprocity and is thus accurate in all frequency ranges. The model takes
into account the absorption in the substrate induced by the particles but does
not take into account the near-field interactions between the particles.Comment: 15 pages, 10 figure
Propagation of light through small clouds of cold interacting atoms
We demonstrate experimentally that a cloud of cold atoms with a size
comparable to the wavelength of light can induce large group delays on a laser
pulse when the laser is tightly focused on it and is close to an atomic
resonance. Delays as large as -10 ns are observed, corresponding to
"superluminal" propagation with negative group velocities as low as -300 m/s.
Strikingly, this large delay is associated with a moderate extinction owing to
the very small size of the cloud and to the light-induced interactions between
atoms. It implies that a large phase shift is imprinted on the continuous laser
beam, and opens interesting perspectives for applications to quantum
technologies.Comment: 5 pages, 3 figures Supplemental Material : 2 pages, 2 Figure
Homogenization of an ensemble of interacting resonant scatterers
We study theoretically the concept of homogenization in optics using an
ensemble of randomly distributed resonant stationary atoms with density .
The ensemble is dense enough for the usual condition for homogenization, viz.
, to be reached. Introducing the coherent and incoherent
scattered powers, we define two criteria to define the homogenization regime.
We find that when the excitation field is tuned in a broad frequency range
around the resonance, none of the criteria for homogenization is fulfilled,
meaning that the condition is not sufficient to
characterize the homogenized regime around the atomic resonance. We interpret
these results as a consequence of the light-induced dipole-dipole interactions
between the atoms, which implies a description of scattering in terms of
collective modes rather than as a sequence of individual scattering events.
Finally, we show that, although homogenization can never be reached for a dense
ensemble of randomly positioned laser-cooled atoms around resonance, it becomes
possible if one introduces spatial correlations in the positions of the atoms
or non-radiative losses, such as would be the case for organic molecules or
quantum dots coupled to a phonon bath.Comment: 9 pages, 5 figures. Corrected mistakes in reference
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