274 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
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
Radiative heat transfer between two dielectric nanogratings in the scattering approach
We present a theoretical study of radiative heat transfer between dielectric
nanogratings in the scattering approach. As a comparision with these exact
results, we also evaluate the domain of validity of Derjaguin's Proximity
Approximation (PA). We consider a system of two corrugated silica plates with
various grating geometries, separation distances, and lateral displacement of
the plates with respect to one another. Numerical computations show that while
the PA is a good approximation for aligned gratings, it cannot be used when the
gratings are laterally displaced. We illustrate this by a thermal modulator
device for nanosystems based on such a displacement
Increasing the bandwidth of coaxial aperture arrays in radar frequencies
Arrays of coaxial cavities in a silver slab are an angle-independent frequency-selective structure in the optical wavelengths. We show that understanding major resonant effects can achieve a similar structure in the radar frequencies. We use a biperiodic boundary integral method to explain the resonances. We suggest a geometrical evolution of the coaxial cavities that presents an enhanced bandwidth under oblique incidence in TM polarizatio
Near-field heat transfer between a nanoparticle and a rough surface
In this work we focus on the surface roughness correction to the near-field
radiative heat transfer between a nanoparticle and a material with a rough
surface utilizing a direct perturbation theory up to second order in the
surface profile. We discuss the different distance regimes for the local
density of states above the rough material and the heat flux analytically and
numerically. We show that the heat transfer rate is larger than that
corresponding to a flat surface at short distances. At larger distances it can
become smaller due to surface polariton scattering by the rough surface. For
distances much smaller than the correlation length of the surface profile, we
show that the results converge to a proximity approximation, whereas in the
opposite limit the rough surface can be replaced by an equivalent surface
layer
Surface plasmon polaritons on thin-slab metal gratings
Ian R. Hooper and J. Roy Sambles, Physical Review B, Vol. 67, article 235404 (2003). "Copyright © 2003 by the American Physical Society."In a recently published paper [U. Schröter and D. Heitmann, Phys. Rev. B 60, 4992 (1999)] an unexpected result occurred when light was incident upon a periodically corrugated thin metal film when the corrugations on the two interfaces were identical and in phase with each other. It was observed that it was not possible to excite the surface plasmon polariton on the metal surface facing away from the incoming light, and they ascribed this to the lack of a thickness variation within the metal. In this paper a somewhat different interpretation of their results is presented, which shows that the surface plasmon polariton (SSP) is in fact very weakly excited on the transmission side of such structures. It is explained why this coupling is so weak in terms of the cancellation of the evanescent diffracted orders from the two diffractive surfaces and how, by changing the phase between the grating on either surface, this coupling becomes much stronger. An explanation for the observation that SPP excitation on such structures may lead to either transmission maxima or minima is also presented
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
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