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IEEE Journal of Quantum Electronics

Experimental versus theoretical rates for photoassociation and for formation of ultracold molecules

Cyril Drag, B. Laburthe-Tolra, Olivier Dulieu, D. Comparat, Mihaela Vatasescu, Salah Boussen, S. Guibal, A. Crubellier, P. Pillet

Published Dec 1, 2000• 66 citations
Publisher

Abstract

We report on the spectra of the long-range attractive molecular states of the Cs/sub 2/ dimer below the dissociation limits 6s+6p/sub 1/2/ and 6s+6p/sub 3/2/ which are accessible by molecular photoassociation of cold Cs atoms. For the states O/sub u//sup +/ and O/sub g//sup -/(6s+6p/sub 3/2/), we have performed trap-loss measurements, which are in good agreement with the theoretical calculations, performed in a perturbative approach. For the O/sub g//sup -/ and 1/sub u/(6s+6p/sub 3/2/) states, we observe, after spontaneous decay of the electronically excited molecules, the formation of translationally cold molecules. A rate of formation of cold molecules of the order of /spl sim/10/sup 6/ molecules per second is obtained in the case of the state O/sub g//sup $/.

DOI
10.1109/3.892556

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The Journal of Chemical Physics•Oct 5, 2004•39 citations
We report on the spectra of the long-range attractive molecular states of the Cs/sub 2/ dimer below the dissociation limits 6s+6p/sub 1/2/ and 6s+6p/sub 3/2/ which are accessible by molecular photoassociation of cold Cs atoms. For the states O/sub u//sup +/ and O/sub g//sup -/(6s+6p/sub 3/2/), we have performed trap-loss measurements, which are in good agreement with the theoretical calculations, performed in a perturbative approach. For the O/sub g//sup -/ and 1/sub u/(6s+6p/sub 3/2/) states, we observe, after spontaneous decay of the electronically excited molecules, the formation of translationally cold molecules. A rate of formation of cold molecules of the order of /spl sim/10/sup 6/ molecules per second is obtained in the case of the state O/sub g//sup $/.
In the molecular photoassociation process, two free cold atoms absorb one photon by a resonant way, to create an excited molecule in a well defined ro-vibrational state. The photoassociative spectroscopy of alkaline dimers yields accurate determinations for the long-range parts of molecular potential curves correlated to the first s + p asymptote. In contrast to atoms, laser cooling of molecules is very difficult because of the lack of a closed two-level scheme for recycling the population. The molecular photoassociation of cold atoms opens also a promising alternative for the formation of cold ground state molecules. Photoassociation of cold cesium atoms has permitted the first observation of translationally cold ground state molecules. The case of the cesium atom is very favorable because the 0 g - and 1 u purely long-range states below the dissociation limit 6s 1/2 +6p 3/2 present Condon points at intermediate distances. Such configurations offer rather efficient channels for the creation of singlet or triplet ground state Cs 2 molecules after spontaneous decay.
We report on the formation of translationally cold Cs2 ground-state molecules through photoassociation of laser-cooled cesium atoms in a magneto-optical trap. The cold molecules are obtained after spontaneous decay of photoassociated molecules, and detected after pulsed-laser photoionization into Cs2+ ions. Photoassociation spectra of cesium attractive molecular states below the 6S1/2+6P3/2 dissociation limits are reported, obtained with both ion detection and trap-loss method. A temperature as low as 20−5+15 has been measured for the molecular cloud.
Summary form only given. In contrast to atoms, laser cooling of molecules is very difficult because of the lack of a closed two-level scheme for recycling the population. The molecular photoassociation of cold atoms opens a promising alternative for the formation of cold molecules. The photoassociative spectra are obtained by the usual trap-loss method as well as by pulsed laser photoionization of Cs/sub 2/ molecules into Cs/sub 2//sup +/ ions. Different schemes to obtain formation of cold molecules through photoassociation will be discussed.
We report on the observation of translationally cold Cs2 molecules at temperatures in the 300–70 μK range, produced by the photoassociation of cold Cs atoms in a vapor-cell magneto-optical trap. The detection method is based on pulsed-laser photoionization of Cs2 molecules into Cs2+ ions, selectively detected through a time-of-flight mass spectrometer. This technique, together with the usual trap-loss method, enables us to perform the spectroscopy of the long-range attractive molecular states below the 6s 2S1/2+6p 2P3/2 dissociation limit.
We calculate the rates of formation and detection of ultracold Cs 2 molecules obtained from the photoassociation of ultracold atoms through the double-well 0 g − (6S 1/2 + 6P 3/2 ) state. We concentrate on two features previously observed experimentally and attributed to tunnelling between the two wells (Vatasescu et al 2000 Phys. Rev. A 61 044701). We show that the molecules obtained are in strongly bound levels ( v ″ = 5, 6) of the metastable a 3 Σ u + (6S 1/2 + 6S 1/2 ) ground electronic state.
High precision photoassociation spectroscopy is performed in ultracold cesium gas, with detunings as large as 51 cm(-1) below the Cs(6S(1/2))+Cs(6P(3/2)) asymptote. Trap-loss fluorescence detection is used for detecting the photoassociation to excited state ultracold molecules. Long vibrational progressions are assigned to electronic states of 0(g) (-), 0(u) (+), and 1(g) symmetry. The spectral data are fitted to a LeRoy-Bernstein equation, in order to obtain the effective coefficients of the leading long-range interaction term (C(3)/R(3)) and the relative vibrational quantum numbers measured down from dissociation. Additionally we present evidence for perturbations between the 0(g) (-) state and the dark 2(u) state.