196 research outputs found
A quantum model for collective recoil lasing
Free Electron Laser (FEL) and Collective Atomic Recoil Laser (CARL) are
described by the same model of classical equations for properly defined scaled
variables. These equations are extended to the quantum domain describing the
particle's motion by a Schr\"{o}dinger equation coupled to a self-consistent
radiation field. The model depends on a single collective parameter
which represents the maximum number of photons emitted per particle. We
demonstrate that the classical model is recovered in the limit , in which the Wigner function associated to the Schr\"{o}dinger equation
obeys to the classical Vlasov equation. On the contrary, for ,
a new quantum regime is obtained in which both FELs and CARLs behave as a
two-state system coupled to the self-consistent radiation field and described
by Maxwell-Bloch equations
The Semiclassical and Quantum Regimes of Superradiant Light Scattering from a Bose-Einstein Condensate
We show that many features of the recent experiments of Schneble et al. [D.
Schneble, Y. Torii, M. Boyd, E.W. Streed, D.E. Pritchard and W. Ketterle,
Science vol. 300, p. 475 (2003)], which demonstrate two different regimes of
light scattering by a Bose-Einstein condensate, can be described using a
one-dimensional mean-field quantum CARL model, where optical amplification
occurs simultaneously with the production of a periodic density modulation in
the atomic medium. The two regimes of light scattering observed in these
experiments, originally described as ``Kapiza-Dirac scattering'' and
``Superradiant Rayleigh scattering'', can be interpreted as the semiclassical
and quantum limits respectively of CARL lasing.Comment: 10 pages, 5 figures - to appear in Journal of Optics
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
Atomic interaction effects in the superradiant light scattering from a Bose-Einstein condensate
We investigate the effects of the atomic interaction in the Superradiant
Rayleigh scattering from a Bose-Einstein condensate driven by a far-detuned
laser beam. We show that for a homogeneous atomic sample the atomic interaction
has only a dispersive effect, whereas in the inhomogeneous case it may increase
the decay of the matter-wave grating.Comment: 12 pages, 4 figures, presented to the XII International Laser Physics
Workshop, August 24-29, Hamburg, to be published in Laser Physic
Quantum theory of SASE FEL
We describe a free-electron laser (FEL) in the Self-Amplified Spontaneous Emission (SASE) regime quantizing the electron motion and taking into account propagation effects. We demonstrate quantum purification of the SASE spectrum, i.e. in a properly defined quantum regime the spiking behavior disappears and the SASE power spectrum becomes very narrow
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
Recoil-induced subradiance in a cold atomic gas
Subradiance, i.e. the cooperative inhibition of spontaneous emission by
destructive interatomic interference, can be realized in a cold atomic sample
confined in a ring cavity and lightened by a two-frequency laser. The atoms,
scattering the photons of the two laser fields into the cavity-mode, recoil and
change their momentum. Under proper conditions the atomic initial momentum
state and the first two momentum recoil states form a three-level degenerate
cascade. A stationary subradiant state is obtained after that the scattered
photons have left the cavity, leaving the atoms in a coherent superposition of
the three collective momentum states. After a semiclassical description of the
process, we calculate the quantum subradiant state and its Wigner function.
Anti-bunching and quantum correlations between the three atomic modes of the
subradiant state are demonstrated
Quantum effects in the collective light scattering by coherent atomic recoil in a Bose-Einstein condensate
We extend the semiclassical model of the collective atomic recoil laser
(CARL) to include the quantum mechanical description of the center-of-mass
motion of the atoms in a Bose-Einstein condensate (BEC). We show that when the
average atomic momentum is less than the recoil momentum , the
CARL equations reduce to the Maxwell-Bloch equations for two momentum levels.
In the conservative regime (no radiation losses), the quantum model depends on
a single collective parameter, , that can be interpreted as the average
number of photons scattered per atom in the classical limit. When ,
the semiclassical CARL regime is recovered, with many momentum levels populated
at saturation. On the contrary, when , the average momentum
oscillates between zero and , and a periodic train of
hyperbolic secant pulses is emitted. In the dissipative regime (large radiation
losses) and in a suitable quantum limit, a sequential superfluorescence
scattering occurs, in which after each process atoms emit a hyperbolic
secant pulse and populate a lower momentum state. These results describe the
regular arrangement of the momentum pattern observed in recent experiments of
superradiant Rayleigh scattering from a BEC.Comment: submitted for publication on Phys. Rev.
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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