65 research outputs found
Dynamique de l'interaction dans un gaz d'atomes de Rydberg froids. Blocage dipolaire, ionisation Penning. Pompage optique et refroidissement de la vibration de molécules
No full textThe main topic of this thesis deals with electrostatic interactions at very long range between Rydberg atoms. Rydberg atoms provide an extremely large polarizability leading in several configurations to dipole-dipole interactions with range that can reach more than 10 microns. Our high-resolution experiments show an inhibition of excitation when interactions between pairs of Rydberg atoms happen close to a resonance and also using an electric field to control the internal coupling between Rydberg states. These results obtained in a macroscopic ensemble have been transposed to a system of two atoms only (collaboration with Institut d'Optique). We then analyze spatial and temporal dynamics of blockade experiments in presence of an electric field using a kinetic Monte Carlo algorithm and we study the formation of ions and their consequences. Observation of Penning ionization for attractive potentials could lead to the formation of a cold plasma but a similar observation for repulsive potentials between two Rydberg atoms indicates a transfer of population driven by blackbody radiation. A second topic is the study of the formation of cold cesium molecules. Broadband lasers were used to detect these cold molecules and to find new schemes for cooling internal degrees of freedom of the cesium dimer. In the latter case the use of a mode-locked femtosecond laser shaped in intensity and frequency allowed us to populate after a few cycles of absorption-spontaneous emission the vibrational state v = 0 of the electronic ground state of the cesium dimer.Le sujet principal de cette thèse concerne les interactions électrostatiques à très longues portés entre atomes de Rydberg. Les atomes de Rydberg offrent une polarisabilité extrêmement importante qui conduit dans plusieurs configurations, à des interactions de type dipôle-dipôle dont la portée peut atteindre plus de 10 microns. Nos expériences à haute résolution montrent une inhibition de l'excitation par un contrôle de l'interaction entre paires d'atomes de Rydberg au voisinage d'une résonance en énergie ainsi que par couplage interne entre niveaux de Rydberg lors de l'application d'un champ électrique. Ces résultats obtenus dans un ensemble macroscopique ont été transposés à un système de deux atomes seulement (collaboration avec l'Institut d'Optique). Nous analysons ensuite la dynamique spatiale et temporelle des expériences de blocage dipolaire en champ électrique à l'aide d'un algorithme Monte Carlo cinétique et nous étudions la formation d'ions et leurs conséquences. L'observation de l'ionisation Penning pour des potentiels attractifs pouvant conduire à un plasma froid mais aussi pour des potentiels répulsifs entre deux atomes de Rydberg indique un rôle de transfert du rayonnement thermique. Un deuxième sujet est l'étude de la formation de molécules froides de césium. Des lasers à large bande spectrale ont été utilisés pour la détection de ces molécules froides et dans des schémas de refroidissement des degrés de liberté internes du dimère de césium. Dans ce dernier cas l'utilisation d'un laser femtoseconde mode bloqué façonné en intensité et en fréquence nous a permis de peupler après quelques cycles d'absorption-émission spontanée l'état vibrationnel v=0 de l'état fondamental du dimère de césium
Institut Français de la Mode — Festival
No full textL'Institut Français de la Mode organise son festival de fin d'année les 1er et 2 juillet. FESTIVAL MODE INSTITUT FRANCAIS DE LA MODE Vendredi 1er juillet 17h "Créativité et interdisciplinarité", par Amodsen Chotia (Centre de Recherches Interdisciplinaires, Paris) 18h "Les temps de la mode, ou la mode et le temps", par Jean-Jacques Picart 19h "Nouveaux modèles de business dans le luxe", par Uriel Karsenti, CEO de Maison Standards. 19h30 : grand témoin : Vanessa Seward avec Luc..
Optical pumping and vibrational cooling of molecules
No full textSUMMARY The methods producing cold molecules from cold atoms tend to leave molecular
ensembles with substantial residual internal energy. For instance, Cs2
molecules initially formed via photoassociation of cold Cs atoms are in several
vibrational levels, v, of the electronic ground state. Here we apply a
broadband femtosecond laser that redistributes the vibrational population in
the ground state via a few electronic excitation - spontaneous emission cycles.
The laser pulses are shaped to remove the excitation frequency band of the v =
0 level, preventing re-excitation from that state. We observe a fast and
efficient accumulation, about 70% of the initially detected molecules, in the
lowest vibrational level, v = 0, of the singlet electronic state. The validity
of this incoherent depopulation pumping method is very general and opens
exciting prospects for laser cooling and manipulation of molecules
Dynamique de l'interaction dans un gaz d'atomes de Rydberg froids
No full textORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF
Photoionization spectroscopy of excited states of cold cesium dimers
No full textSUMMARY Photoionization spectroscopy of cold cesium dimers obtained by
photoassociation of cold atoms in a magneto-optical trap is reported here. In
particular, we report on the observation and on the spectroscopic analysis of
all the excited states that have actually been used for efficient detection of
cold molecules stabilized in the triplet a^3Sigma_u^+ ground state. They are:
the (1)^3Sigma_g^+ state connected to the 6s+6p asymptote, the (2)^3Sigma_g^+
and (2)^3Pi_g states connected to the 6s+5d asymptote and finally the
(3)^3Sigma_g^+ state connected to the 6s + 7s asymptote. The detection through
these states spans a wide range of laser energies, from 8000 to 16500 cm-1,
obtained with different laser dyes and techniques. Information on the initial
distribution of cold molecules among the different vibrational levels of the
a^3Sigma_u^+ ground state is also provided. This spectroscopic knowledge is
important when conceiving schemes for quantum manipulation, population transfer
and optical detection of cold cesium molecules
Efficient formation of deeply bound ultracold molecules probed by broadband detection
No full textSUMMARY Using a non-selective broadband detection scheme we discovered an efficient
mechanism of formation of ultracold Cs molecules in deeply bound levels
() of their electronic ground state X. They are formed by
a one-photon photoassociation of ultracold cesium atoms in a manifold of
excited electronic states, followed by a two-step spontaneous emission cascade.
We were able to form about molecules per second in these low
vibrational levels of the ground state. This detection scheme could be
generalized to other molecular species for the systematic investigation of cold
molecule formation mechanisms
Aux frontières des plasmas : les plasmas ultra-froids
No full textUn nouveau type de plasma, dit ultra-froid, a récemment été réalisé en laboratoire en utilisant des collisions entre atomes excités dans un état de Rydberg , ou en ionisant, grâce à un laser, un gaz à une température proche du zéro absolu. Les chercheurs essaient actuellement de refroidir ces plasmas et de les piéger tout en étudiant leurs propriétés particulières, comme une possible cristallisation spontanée en régime fortement corrélé
Kinetic Monte Carlo modelling of dipole blockade in Rydberg excitation experiment
No full text23 pages. Accepted for publication in New Journal of Physics.We present a method to model the interaction and the dynamics of atoms excited to Rydberg states. We show a way to solve the optical Bloch equations for laser excitation of the frozen gas in good agreement with the experiment. A second method, the Kinetic Monte Carlo method gives an exact solution of rate equations. Using a simple N-body integrator (Verlet), we are able to describe dynamical processes in space and time. Unlike more sophisticated methods, the Kinetic Monte Carlo simulation offers the possibility of numerically following the evolution of tens of thousands of atoms within a reasonable computation time. The Kinetic Monte Carlo simulation gives good agreement with dipole-blockade type of experiment. The role of ions and the individual particle effects are investigated
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