176 research outputs found
Anisotropic Atom-Surface Interactions in the Casimir-Polder Regime
The distance-dependence of the anisotropic atom-wall interaction is studied.
The central result is the 1/z^6 quadrupolar anisotropy decay in the retarded
Casimir-Polder regime. Analysis of the transition region between non-retarded
van der Waals regime (in 1/z^3) and Casimir-Polder regime shows that the
anisotropy cross-over occurs at very short distances from the surface, on the
order of 0.03 Lambda, where Lambda is the atom characteristic wavelength.
Possible experimental verifications of this distance dependence are discussed.Comment: 5 pages, 2 figure
Detection of Spiral photons in Quantum Optics
We show that a new type of photon detector, sensitive to the gradients of
electromagnetic fields, should be a useful tool to characterize the quantum
properties of spatially-dependent optical fields. As a simple detector of such
a kind, we propose using magnetic dipole or electric quadrupole transitions in
atoms or molecules and apply it to the detection of spiral photons in
Laguerre-Gauss (LG) beams. We show that LG beams are not true hollow beams, due
to the presence of magnetic fields and gradients of electric fields on beam
axis. This approach paves the way to an analysis at the quantum level of the
spatial structure and angular momentum properties of singular light beams.Comment: 5 pages, 4 figure
Negative-index media for matter-wave optics
We consider the extension of optical meta-materials to matter waves. We show
that the generic property of pulsed comoving magnetic fields allows us to
fashion the wave-number dependence of the atomic phase shift. It can be used to
produce a transient negative group velocity of an atomic wave packet, which
results into a negative refraction of the matter wave. Application to slow
metastable argon atoms Ar*(3P2) shows that the device is able to operate either
as an efficient beam splitter or an atomic meta-lens. Implications of
"meta-media" in atom optics are considered.Comment: 4 pages, 4 figures, submitted at PRL 4 November 200
Coherent flash of light emitted by a cold atomic cloud
When a resonant laser sent on an optically thick cold atomic cloud is
abruptly switched off, a coherent flash of light is emitted in the forward
direction. This transient phenomenon is observed due to the highly resonant
character of the atomic scatterers. We analyze quantitatively its
spatio-temporal properties and show very good agreement with theoretical
predictions. Based on complementary experiments, the phase of the coherent
field is reconstructed without interferometric tools.Comment: Submitted to Phys. Rev. Let
Selective Reflection Spectroscopy at the Interface between a Calcium Fluoride Window and Cs Vapour
A special vapour cell has been built, that allows the measurement of the
atom-surface van der Waals interaction exerted by a CaF2 window at the
interface with Cs vapour. Mechanical and thermal fragility of fluoride windows
make common designs of vapour cells unpractical, so that we have developed an
all-sapphire sealed cell with an internal CaF2 window. Although impurities were
accidentally introduced when filling-up the prototype cell, leading to a
line-broadening and shift, the selective reflection spectrum on the Cs D1 line
(894 nm) makes apparent the weak van der Waals surface interaction. The
uncertainties introduced by the effects of these impurities in the van der
Waals measurement are nearly eliminated when comparing the selective reflection
signal at the CaF2 interface of interest, and at a sapphire window of the same
cell. The ratio of the interaction respectively exerted by a sapphire interface
and a CaF2 interface is found to be 0.55 0.25, in good agreement with the
theoretical evaluation of ~0.67.Comment: soumis \`a Appl Phys B MS 4734
Selective Reflection Spectroscopy on the UV Third Resonance Line of Cs : Simultaneous Probing of a van der Waals Atom-Surface Interaction Sensitive to Far IR Couplings and of Interatomic Collisions
We report on the analysis of FM selective reflection experiments on the
6S1/2->8P3/2 transition of Cs at 388 nm, and on the measurement of the surface
van der Waals interaction exerted by a sapphire interface on Cs(8P3/2). Various
improvements in the systematic fitting of the experiments have permitted to
supersede the major difficulty of a severe overlap of the hyperfine components,
originating on the one hand in a relatively small natural structure, and on the
other hand on a large pressure broadening imposed by the high atomic density
needed for the observation of selective reflection on a weak transition. The
strength of the van der Waals surface interaction is evaluated to be 7310
kHz.m3. An evaluation of the pressure shift of the transition is also
provided as a by-product of the measurement. We finally discuss the
significance of an apparent disagreement between the experimental measurement
of the surface interaction, and the theoretical value calculated for an
electromagnetic vacuum at a null temperature. The possible influence of the
thermal excitation of the surface is evoked, because, the dominant
contributions to the vW interaction for Cs(8P3/2) lie in the far infrared
range.Comment: submitted to Laser Physics - issue in the memory of Herbert Walther
Quadrupole transitions near interface: general theory and application to atom inside a planar cavity
Quadrupole radiation of an atom in an arbitrary environment is investigated
within classical as well as quantum electrodynamical approaches. Analytical
expressions for decay rates are obtained in terms of Green function of Maxwell
equations. The equivalence of both approaches is shown. General expressions are
applied to analyze the quadrupole decay rate of an atom placed between two half
spaces with arbitrary dielectric constant. It is shown that in the case when
the atom is close to the surface, the total decay rate is inversely
proportional to the fifth power of distance between an atom and a plane
interface.Comment: 18 pages, 7 figure
Dynamics of evanescent matter waves in negative-index media
International audiencenumbers: 03.75.-b Matter Waves 03.75.Be Atom and Neutron Optics 37.10.Gh Atom Traps and Guides 42.25.-p Wave Optics ABSTRACT Semi-evanescent and evanescent matter-waves produced by an atom wave packet impinging a repulsive barrier can be back-refracted and reconstructed by the application of negative-index " comoving " potential pulses. One shows that those collapses and revivals generate a matter wave confined on both sides of the barrier border (" surface matter wave ") and should be observable via the retardation of atom reflection from the barrier interface. This property, joined to the possibility recently demonstrated of inducing negative refraction of atom waves, makes such potentials a matter-wave counterpart of negative-index materials or " meta materials " well-known in light optics
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