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Photoassociation inside an optical dipole trap: absolute rate coefficients and Franck-Condon factors

Wester, R, Kraft, S D, Marcel Carto Constantin Mudrich, Staudt, M U, Lange, J, Nicolas Vanhaecke, Olivier Dulieu, Matthias Weidemüller

Published Oct 1, 2004• 19 citations
OpenAlex

Abstract

We present quantitative measurements of the photoassociation of cesium molecules inside a far-detuned optical dipole trap. A model of the trap depletion dynamics is derived which allows to extract absolute photoassociation rate coefficients for the initial single-photon photoassociation step from measured trap-loss spectra. The sensitivity of this approach is demonstrated by measuring the Franck-Condon modulation of the weak photoassociation transitions into the low vibrational levels of the outer well of the 0g- state that correlates to the 6s+6p3/2 asymptote. The measurements are compared to theoretical predictions. In a magneto-optical trap these transitions have previously only been observed indirectly through ionization of ground state molecules.

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We report the spectroscopy of molecular $1_{g}, 0^{+}_{u}, 0^{-}_{g}$ and $1_{u}$ state potentials below the dissociattion limit $6s^{2}S_{1/2}+6p^{2}P_{3/2}$ by using the molecular photoassociation technique of cold Cs atoms, in a vapor-cell magneto-optical trap. The $1_{g}$ and $0^{+}_{g}$ states are detected by trap losses. The $0^{-}_{g}$ and $1_{u}$ states, which lead to the formation of cold molecules [1], are detected by photoionizing them into $Cs_{2}^{+}$ and detecting with a time-of-flight mass spectrometer, while the $l_{g}$ and $0^{+}_{u}$ states are detected by trap losses. We give the spectra of the whole series $0^{-}_{g}$ and $1_{u}$. The $0^{-}_{g}$ series is analyzed in a RKR approach and the hyperfine structure of the $1_{u}$ series will be discussed. The observed modulation of intensities of the lines is due to Franck Condon factors characterizing the photoassociative transition between the initial state of two free atoms and the finalro-vibrational level. The intensity modulation can give access to the scattering lengths of the ground state. This possibility will be discussed.

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We present an ultra-high resolution spectroscopic study of the photoassociation of cesium atoms inside a magnetooptical trap using trap-loss detection with photoassociation laser slow scanning. The photoassociation spectra show vibrational levels of three molecular symmetries below the 6S 1/2 + 6P 3/2 dissociation limit. A dynamic model is derived to extract the photoassociation rate from the trap-loss spectrum. Many observed rotational levels are well resolved, which indicate d-wave and higher partial wave contributions to the photoassociation cross section.

Laser Physics•Sep 1, 2007•6 citations
We present quantitative measurements of the photoassociation of cesium molecules inside a far-detuned optical dipole trap. A model of the trap depletion dynamics is derived which allows to extract absolute photoassociation rate coefficients for the initial single-photon photoassociation step from measured trap-loss spectra. The sensitivity of this approach is demonstrated by measuring the Franck-Condon modulation of the weak photoassociation transitions into the low vibrational levels of the outer well of the 0g- state that correlates to the 6s+6p3/2 asymptote. The measurements are compared to theoretical predictions. In a magneto-optical trap these transitions have previously only been observed indirectly through ionization of ground state molecules.
We present studies of strong coupling in single-photon photoassociation of cesium dimers using an optical dipole trap. A thermodynamic model of the trap depletion dynamics is employed to extract absolute rate coefficents. From the dependence of the rate coefficient on the photoassociation laser intensity, we observe saturation of the photoassociation scattering probability at the unitarity limit in quantitative agreement with the theoretical model by Bohn and Julienne [Phys. Rev. A 60, 414 (1999)]. Also the corresponding power broadening of the resonance width is measured. We could not observe an intensity-dependent light shift in contrast to findings for lithium and rubidium, which is attributed to the absence of a ppp- or ddd-wave shape resonance in cesium.
PHOTOASSOCIATIVE SPECTROSCOPY OF Cs2Cs_{2}Cs2​ MOLECULE
We report the spectroscopy of molecular 1g,0u+,0g−1_{g}, 0^{+}_{u}, 0^{-}_{g}1g​,0u+​,0g−​ and 1u1_{u}1u​ state potentials below the dissociattion limit 6s2S1/2+6p2P3/26s^{2}S_{1/2}+6p^{2}P_{3/2}6s2S1/2​+6p2P3/2​ by using the molecular photoassociation technique of cold Cs atoms, in a vapor-cell magneto-optical trap. The 1g1_{g}1g​ and 0g+0^{+}_{g}0g+​ states are detected by trap losses. The 0g−0^{-}_{g}0g−​ and 1u1_{u}1u​ states, which lead to the formation of cold molecules [1], are detected by photoionizing them into Cs2+Cs_{2}^{+}Cs2+​ and detecting with a time-of-flight mass spectrometer, while the lgl_{g}lg​ and 0u+0^{+}_{u}0u+​ states are detected by trap losses. We give the spectra of the whole series 0g−0^{-}_{g}0g−​ and 1u1_{u}1u​. The 0g−0^{-}_{g}0g−​ series is analyzed in a RKR approach and the hyperfine structure of the 1u1_{u}1u​ series will be discussed. The observed modulation of intensities of the lines is due to Franck Condon factors characterizing the photoassociative transition between the initial state of two free atoms and the finalro-vibrational level. The intensity modulation can give access to the scattering lengths of the ground state. This possibility will be discussed.
We study the photoassociative collisional loss of laser-cooled Rb atoms from a far-off resonance optical dipole force atom trap. We obtain a well-resolved photoassociation spectrum from 50 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ to 980 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ below the first excited dissociation limit of the Rb2{\mathrm{Rb}}_{2}Rb2​ molecule. Two vibrational series associated with excited Rb2{\mathrm{Rb}}_{2}Rb2​ $^{3}\mathrm{\ensuremath{\Sigma}}_{\mathit{g}}^{+}$ states are clearly visible. Oscillations in the associated Franck-Condon factors reflect the structure of the triplet ground state wave function. Our results clearly demonstrate the potential of photoassociation spectroscopy as a new probe of molecular structure.
The field of laser cooling and trapping of atoms has had a profound impact on many areas of atomic, molecular and optical science. In particular, ultracold atoms colliding in magneto-optical traps typically have relative kinetic energies of 300muK(sim7MHz)300\\mu K (\\sim 7 MHz)300muK(sim7MHz), so free-bound absorption lines are as sharp as bound-bound lines. Moreover, because of very long range centrifugal barriers, only a few collisional partial waves are important (Jprimeprime=0,1J^{\\prime\\prime} = 0, 1Jprimeprime=0,1 and 2 in our work on 39K^{39}K39K). Such photoassociative free-bound absorption allows observation of ``pure long-range molecule'' states (Re=28R_{e} = 28Re​=28 and 39 {\\AA} in 39K2^{39}K_{2}39K2​) as well as long-range levels of known short range states with outer classical turning points of sim20−250AA\\sim 20 - 250 {\\AA}sim20−250AA. Such spectra have been observed by ``trap loss'' (decrease in atomic fluorescence), molecular ionization, and fragment ionization. Optical-optical double resonance (OODR), e.g. through the ``Franck-Condon windows'' of the ``pure long-range'' states, produces readily assignable spectra at higher asymptotes as well. Further extensions of ultracold photoassociative spectroscopy and applications to determination of long range potentials, atomic properties, and Bose-Einstein condensate stability will be presented.
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.
We present an ultra-high resolution spectroscopic study of the photoassociation of cesium atoms inside a magnetooptical trap using trap-loss detection with photoassociation laser slow scanning. The photoassociation spectra show vibrational levels of three molecular symmetries below the 6S 1/2 + 6P 3/2 dissociation limit. A dynamic model is derived to extract the photoassociation rate from the trap-loss spectrum. Many observed rotational levels are well resolved, which indicate d-wave and higher partial wave contributions to the photoassociation cross section.