J. Léonard

Giant helium dimers produced by photoassociation of ultracold metastable atoms.

We produce giant, purely long-range helium dimers by photoassociation of metastable helium atoms in a magnetically trapped, ultracold cloud. The photoassociation laser is detuned close to the atomic 2(3)S1-2(3)P0 line and produces strong heating of the sample when resonant with molecular bound states. The temperature of the cloud serves as an indicator of the molecular spectrum. We report good agreement between our spectroscopic measurements and our calculations of the five bound states belonging to a 0(+)(u) purely long-range potential well. These previously unobserved states have classical inner turning points of about 150a(0) and outer turning points as large as 1150a(0).

Penning collisions of laser-cooled metastable helium atoms

Abstract:We present experimental results on the two-body loss rates in a magneto-optical trap of metastable helium atoms. Absolute rates are measured in a systematic way for several laser detunings ranging from -5 to -30 MHz and at different intensities, by monitoring the decay of the trap fluorescence. The dependence of the two-body loss rate coefficient β on the excited state ( 23P2) and metastable state ( 23S1) populations is also investigated. From these results we infer a rather uniform rate constant Ksp = (1±0.4)×10-7 cm3/s.

Analysis of photoassociation spectra for giant helium dimers

We perform a theoretical analysis to interpret the spectra of purely long-range helium dimers produced by photoassociation (PA) in an ultracold gas of metastable helium atoms. The experimental spectrum obtained with the PA laser tuned closed to the 2 3 S1

Rotationally induced Penning ionization of ultracold photoassociated helium dimers

2 3 P0 atomic line has been reported in a previous paper. Here, we first focus on the corrections to be applied to the measured resonance frequencies in order to infer the molecular binding energies. We then present a calculation of the vibrational spectra for the purely long-range molecular states, using adiabatic potentials obtained from perturbation theory. With retardation effects taken into account, the agreement between experimental and theoretical determinations of the spectrum for the 0 u purely long-range potential well is very good. The results yield a determination of the lifetime of the 2 3 P atomic state.

Production of a Bose Einstein condensate of metastable helium atoms

We have studied photoassociation of metastable 23S1 helium atoms near the 23S1-23P2 asymptote by both ion detection in a magneto-optical trap and trap-loss measurements in a magnetic trap. A detailed comparison between the results of the two experiments gives insight into the mechanism of the Penning ionization process. We have identified four series of resonances corresponding to vibrational molecular levels belonging to different rotational states in two potentials. The corresponding spin states become quasi-purely quintet at small interatomic distance, and Penning ionization is inhibited by spin conservation rules. Only a weak rotational coupling is responsible for the contamination by singlet spin states leading to a detectable ion signal. However, for one of these series, Bose statistics does not enable the rotational coupling and the series detected through trap-loss does not give rise to sufficient ionization for detection.

Penning collisions in a cold gas of trapped metastable helium atoms

We recently observed a Bose-Einstein condensate in a dilute gas of He in the 2S1 metastable state. In this article, we describe the successive experimental steps which led to the Bose-Einstein transition at 4.7 μK: loading of a large number of atoms in a MOT, efficient transfer into a magnetic Ioffé-Pritchard trap, and optimization of the evaporative cooling ramp. Quantitative measurements are also given for the rates of elastic and inelastic collisions, both above and below the transition. PACS. 32.80.Pj Optical cooling of atoms; trapping – 03.75.Fi Phase coherent atomic ensembles; quantum condensation phenomena – 05.30.Jp Boson systems

Bose-Einstein Condensation of Metastable Helium

We report progress on an experiment on trapped metastable /sup 4/He(2/sup 3/S/sub 1/) atoms which aims at producing a dense gas of ultra cold atoms, with the goal of reaching Bose-Einstein condensation. We have built a magneto-optical trap (MOT) in which we study the cold collisions, which are the main loss cause limiting the obtainable density.