993 research outputs found
Localization versus subradiance in three-dimensional scattering of light
We study the scattering modes of light in a three-dimensional disordered
medium, in the scalar approximation and above the critical density for Anderson
localization. Localized modes represent a minority of the total number of
modes, even well above the threshold density, whereas spatially extended
subradiant modes predominate. For specific energy ranges however, almost all
modes are localized, yet adjusting accordingly the probe frequency does not
allow to address these only in the regime accessible numerically. Finally,
their lifetime is observed to be dominated by finite-size effects, and more
specifically by the ratio of the localization length to their distance to the
system boundaries.Comment: Add figure comparing localization percentage via frequency, fixed
text, addition of Ioffe-Regel criterion limits, figure axis were normalize
The Atomic Lighthouse Effect
We investigate the deflection of light by a cold atomic cloud when the
light-matter interaction is locally tuned via the Zeeman effect using magnetic
field gradients. This "lighthouse" effect is strongest in the single-scattering
regime, where deviation of the incident field is largest. For optically dense
samples, the deviation is reduced by collective effects, as the increase in
linewidth leads to a decrease of the magnetic field efficiency
Microscopic theory of photonic band gaps in optical lattices
We propose a microscopic model to describe the scattering of light by atoms
in optical lattices. The model is shown to efficiently capture Bragg
scattering, spontaneous emission and photonic band gaps. A connection to the
transfer matrix formalism is established in the limit of a one-dimensional
optical lattice, and we find the two theories to yield results in good
agreement. The advantage of the microscopic model is, however, that it suits
better for studies of finite-size and disorder effects.Comment: 5 pages, 6 figure
Mirror-assisted coherent backscattering from the Mollow sidebands
In front of a mirror, the radiation of weakly driven large disordered clouds
presents an interference fringe in the backward direction, on top of an
incoherent background. Although strongly driven atoms usually present little
coherent scattering, we here show that the mirror-assisted version can produce
high contrast fringes, for arbitrarily high saturation parameters. The contrast
of the fringes oscillates with the Rabi frequency of the atomic transition and
the distance between the mirror and the atoms, due to the coherent interference
between the carrier and the Mollow sidebands of the saturated resonant
fluorescence spectrum emitted by the atoms. The setup thus represents a
powerful platform to study the spectral properties of ensembles of correlated
scatterers
Reducing or enhancing chaos using periodic orbits
A method to reduce or enhance chaos in Hamiltonian flows with two degrees of
freedom is discussed. This method is based on finding a suitable perturbation
of the system such that the stability of a set of periodic orbits changes
(local bifurcations). Depending on the values of the residues, reflecting their
linear stability properties, a set of invariant tori is destroyed or created in
the neighborhood of the chosen periodic orbits. An application on a
paradigmatic system, a forced pendulum, illustrates the method
Stabilizing the intensity of a wave amplified by a beam of particles
The intensity of an electromagnetic wave interacting self-consistently with a
beam of charged particles as in a free electron laser, displays large
oscillations due to an aggregate of particles, called the macro-particle. In
this article, we propose a strategy to stabilize the intensity by re-shaping
the macro-particle. This strategy involves the study of the linear stability
(using the residue method) of selected periodic orbits of a mean-field model.
As parameters of an additional perturbation are varied, bifurcations occur in
the system which have drastic effect on the modification of the self-consistent
dynamics, and in particular, of the macro-particle. We show how to obtain an
appropriate tuning of the parameters which is able to strongly decrease the
oscillations of the intensity without reducing its mean-value
Mode-locked Bloch oscillations in a ring cavity
We present a new technique for stabilizing and monitoring Bloch oscillations
of ultracold atoms in an optical lattice under the action of a constant
external force. In the proposed scheme, the atoms also interact with a
unidirectionally pumped optical ring cavity whose one arm is collinear with the
optical lattice. For weak collective coupling, Bloch oscillations dominate over
the collective atomic recoil lasing instability and develop a synchronized
regime in which the atoms periodically exchange momentum with the cavity field.Comment: 7 pages, 5 figure
Synchronization of Bloch oscillations by a ring cavity
We consider Bloch oscillations of ultracold atoms stored in a one-dimensional
vertical optical lattice and simultaneously interacting with a unidirectionally
pumped optical ring cavity whose vertical arm is collinear with the optical
lattice. We find that the feedback provided by the cavity field on the atomic
motion synchronizes Bloch oscillations via a mode-locking mechanism, steering
the atoms to the lowest Bloch band. It also stabilizes Bloch oscillations
against noise, and even suppresses dephasing due to atom-atom interactions.
Furthermore, it generates periodic bursts of light emitted into the
counter-propagating cavity mode, providing a non-destructive monitor of the
atomic dynamics. All these features may be crucial for future improvements of
the design of atomic gravimeters based on recording Bloch oscillations.Comment: 14 pages, 7 figure
The sound of violets: the ethnographic potency of poetry?
This paper takes the form of a dialogue between the two authors, and is in two halves, the first half discursive and propositional, and the second half exemplifying the rhetorical, epistemological and metaphysical affordances of poetry in critically scrutinising the rhetoric, epistemology and metaphysics of educational management discourse.
Phipps and Saunders explore, through ideas and poems, how poetry can interrupt and/or illuminate dominant values in education and in educational research methods, such as:
âą alternatives to the military metaphors â targets, strategies and the like â that dominate the soundscape of education;
âą the kinds and qualities of the cognitive and feeling spaces that might be opened up by the shifting of methodological boundaries;
âą the considerable work done in ethnography on the use of the poetic: anthropologists have long used poetry as a medium for expressing their sense of empathic connection to their field and their subjects, particularly in considering the creativity and meaning-making that characterise all human societies in different ways;
âą the particular rhetorical affordances of poetry, as a discipline, as a practice, as an art, as patterned breath; its capacity to shift phonemic, and therewith methodological, authority; its offering of redress to linear and reductive attempts at scripting social life, as always already given and without alternative
Cooperative cooling in a one-dimensional chain of optically bound cold atoms
We discuss theoretically the optical binding of one-dimensional chains of cold atoms shone by a transversepump, where particles self-organize to a distance close to an optical wavelength. As the number of particlesis increased, the trapping potential increases logarithmically as the contributions from all atoms add upconstructively. We identify a cooperative cooling mechanism, due to the mutual exchange of photons betweenatoms, which can beat the spontaneous emission for chains that are long enough. Surprisingly, the cooling isoptimal very close to the resonance. This peculiar cooling mechanism thus gives new insights into the cooperativephysics of low-dimensional cold atom systems
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