D. Hennequin - Academia.edu (original) (raw)

Papers by D. Hennequin

Springer Proceedings in Physics, 1992

Physical Review Letters, 2000

The instabilities observed in the atomic cloud of a magneto-optical trap are experimentally studi... more The instabilities observed in the atomic cloud of a magneto-optical trap are experimentally studied through the dynamics of the center of mass location and the cloud population. Two dynamical components are identified: a slow, stochastic one affects both variables, and a fast, deterministic one affects only the center of mass location. A one-dimensional stochastic model taking into account the shadow effect is developed from these observations and reproduces the experimental behavior. It is shown that instabilities are driven by noise and present stochastic resonancelike characteristics.

Physical Review A, 1996

A method enabling atomic velocity class selection by means of quantum interference in the two-pho... more A method enabling atomic velocity class selection by means of quantum interference in the two-photon ionization of an atom through two quasiresonant intermediate levels is studied. This method is compatible with the Doppler cooling in optical molasses, and it is able to attain temperatures colder than the Doppler limit. The advantages and limitations of this method are discussed. We study the effect of the competition with the Doppler cooling for temperatures lower than the Doppler limit, when the usual Doppler process heats the atoms rather than cools them. The method is shown to be limited essentially by the loss of ground-state atoms due to ionization. We also propose and study a ``source'' scheme in which new atoms are continuously injected into the system, leading to a nonvanishing stationary number of cold atoms. Finally, we propose generalizations of the method that allows us to combine it with Sisyphus-type mechanisms.

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2010

Email alerting service here in the box at the top right-hand corner of the article or click Recei... more Email alerting service here in the box at the top right-hand corner of the article or click Receive free email alerts when new articles cite this article -sign up http://rsta.royalsocietypublishing.org/subscriptions go to: Phil. Trans. R. Soc. A To subscribe to

Journal de Physique III, 1994

The European Physical Journal D, 2011

An exhaustive kinetic model for the atoms in a 1D Magneto-Optical Trap is derived, without any ap... more An exhaustive kinetic model for the atoms in a 1D Magneto-Optical Trap is derived, without any approximations. It is shown that the atomic density is described by a Vlasov-Fokker-Planck equation, coupled with two simple differential equations describing the trap beam propagation. The analogy of such a system with plasmas is discussed. This set of equations is then simplified through some approximations, and it is shown that corrective terms have to be added to the models usually used in this context.

The European Physical Journal D - Atomic, Molecular and Optical Physics, 2004

The cloud of cold atoms obtained from a magneto-optical trap is known to exhibit two types of ins... more The cloud of cold atoms obtained from a magneto-optical trap is known to exhibit two types of instabilities in the regime of high atomic densities: stochastic instabilities and deterministic instabilities. In the present paper, the experimentally observed stochastic dynamics is described extensively. It is shown that it exists a variety of dynamical behaviors, which differ by the frequency components appearing in the dynamics. Indeed, some instabilities exhibit only low frequency components, while in other cases, a second time scale, corresponding to a higher frequency, appears in the motion of the center of mass of the cloud. A one-dimensional stochastic model taking into account the shadow effect is shown to be able to reproduce the experimental behavior, linking the existence of instabilities to folded stationary solutions where noise response is enhanced. The different types of regimes are explained by the existence of a relaxation frequency, which in some conditions is excited by noise. PACS. 32.80.Pj Optical cooling of atoms; trapping -05.40.Ca Noise -05.45.-a Nonlinear dynamics and nonlinear dynamical systems

Chaos, Solitons & Fractals, 1994

ABSTRACT The transverse dynamics of a multimode CO2 laser with SF6 as an intracavity saturable ab... more ABSTRACT The transverse dynamics of a multimode CO2 laser with SF6 as an intracavity saturable absorber is experimentally studied. Generalized multistability, periodic alternance and passive Q-switching involving several laser transverse modes have been observed. The dynamics is more particularly studied in the simplest case of the bimode laser where antiphase and in-phase self-oscillations are obtained. In the highly multimode case, experimental conditions are found in which the absorber acts as a mode filter that reduces complex transverse patterns to almost pure Hermite-Gauss modes.

Springer Proceedings in Physics, 1992

Physical Review Letters, 2000

The instabilities observed in the atomic cloud of a magneto-optical trap are experimentally studi... more The instabilities observed in the atomic cloud of a magneto-optical trap are experimentally studied through the dynamics of the center of mass location and the cloud population. Two dynamical components are identified: a slow, stochastic one affects both variables, and a fast, deterministic one affects only the center of mass location. A one-dimensional stochastic model taking into account the shadow effect is developed from these observations and reproduces the experimental behavior. It is shown that instabilities are driven by noise and present stochastic resonancelike characteristics.

Physical Review A, 1996

A method enabling atomic velocity class selection by means of quantum interference in the two-pho... more A method enabling atomic velocity class selection by means of quantum interference in the two-photon ionization of an atom through two quasiresonant intermediate levels is studied. This method is compatible with the Doppler cooling in optical molasses, and it is able to attain temperatures colder than the Doppler limit. The advantages and limitations of this method are discussed. We study the effect of the competition with the Doppler cooling for temperatures lower than the Doppler limit, when the usual Doppler process heats the atoms rather than cools them. The method is shown to be limited essentially by the loss of ground-state atoms due to ionization. We also propose and study a ``source'' scheme in which new atoms are continuously injected into the system, leading to a nonvanishing stationary number of cold atoms. Finally, we propose generalizations of the method that allows us to combine it with Sisyphus-type mechanisms.

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2010

Email alerting service here in the box at the top right-hand corner of the article or click Recei... more Email alerting service here in the box at the top right-hand corner of the article or click Receive free email alerts when new articles cite this article -sign up http://rsta.royalsocietypublishing.org/subscriptions go to: Phil. Trans. R. Soc. A To subscribe to

Journal de Physique III, 1994

The European Physical Journal D, 2011

An exhaustive kinetic model for the atoms in a 1D Magneto-Optical Trap is derived, without any ap... more An exhaustive kinetic model for the atoms in a 1D Magneto-Optical Trap is derived, without any approximations. It is shown that the atomic density is described by a Vlasov-Fokker-Planck equation, coupled with two simple differential equations describing the trap beam propagation. The analogy of such a system with plasmas is discussed. This set of equations is then simplified through some approximations, and it is shown that corrective terms have to be added to the models usually used in this context.

The European Physical Journal D - Atomic, Molecular and Optical Physics, 2004

The cloud of cold atoms obtained from a magneto-optical trap is known to exhibit two types of ins... more The cloud of cold atoms obtained from a magneto-optical trap is known to exhibit two types of instabilities in the regime of high atomic densities: stochastic instabilities and deterministic instabilities. In the present paper, the experimentally observed stochastic dynamics is described extensively. It is shown that it exists a variety of dynamical behaviors, which differ by the frequency components appearing in the dynamics. Indeed, some instabilities exhibit only low frequency components, while in other cases, a second time scale, corresponding to a higher frequency, appears in the motion of the center of mass of the cloud. A one-dimensional stochastic model taking into account the shadow effect is shown to be able to reproduce the experimental behavior, linking the existence of instabilities to folded stationary solutions where noise response is enhanced. The different types of regimes are explained by the existence of a relaxation frequency, which in some conditions is excited by noise. PACS. 32.80.Pj Optical cooling of atoms; trapping -05.40.Ca Noise -05.45.-a Nonlinear dynamics and nonlinear dynamical systems

Chaos, Solitons & Fractals, 1994

ABSTRACT The transverse dynamics of a multimode CO2 laser with SF6 as an intracavity saturable ab... more ABSTRACT The transverse dynamics of a multimode CO2 laser with SF6 as an intracavity saturable absorber is experimentally studied. Generalized multistability, periodic alternance and passive Q-switching involving several laser transverse modes have been observed. The dynamics is more particularly studied in the simplest case of the bimode laser where antiphase and in-phase self-oscillations are obtained. In the highly multimode case, experimental conditions are found in which the absorber acts as a mode filter that reduces complex transverse patterns to almost pure Hermite-Gauss modes.