[show abstract][hide abstract] ABSTRACT: We investigate the dynamics of molecular photoexcitation by unchirped
femtosecond laser pulses using RbCs as a model system. This study is motivated
by a goal of optimizing a two-color scheme of transferring
vibrationally-excited ultracold molecules to their absolute ground state. In
this scheme the molecules are initially produced by photoassociation or
magnetoassociation in bound vibrational levels close to the first dissociation
threshold. We analyze here the first step of the two-color path as a function
of pulse intensity from the low-field to the high-field regime. We use two
different approaches, a global one, the 'Wavepacket' method, and a restricted
one, the 'Level by Level' method where the number of vibrational levels is
limited to a small subset. The comparison between the results of the two
approaches allows one to gain qualitative insights into the complex dynamics of
the high-field regime. In particular, we emphasize the non-trivial and
important role of far-from-resonance levels which are adiabatically excited
through 'vertical' transitions with a large Franck-Condon factor. We also point
out spectacular excitation blockade due to the presence of a quasi-degenerate
level in the lower electronic state. We conclude that selective transfer with
femtosecond pulses is possible in the low-field regime only. Finally, we extend
our single-pulse analysis and examine population transfer induced by coherent
trains of low-intensity femtosecond pulses.
Physical Review A 03/2012; 85(3). · 3.04 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present systematic calculations of the lifetimes of vibrational levels of excited Rb(5s)Cs(6p(1/2)) 0(+) electronic states. We show that a precise description of the variation with the internuclear distance of the transition dipole moment between electronic states is essential. It is also crucial to account precisely for the spin-orbit coupling between the Rb(5s)Cs(6p) A (1)Σ(+) and b (3)Π states. We describe the general trends of the probability of formation of stable molecules in the Rb(5s)Cs(6s) X (1)Σ(+) and a (3)Σ(+) electronic states, through radiative decay from the 0(+)v' levels, together with the branching ratios for the obtention of singlet or triplet molecules, stable with respect to dissociation. Furthermore, this analysis allows us to demonstrate the efficiency of the Mapped Fourier Grid Hamiltonian Representation method (MFGHR) to determine rigorously the energy variation, throughout the continuous part of the spectrum, of the density of an observable connecting bound vibrational levels and continuum states. The resolution in energy can be adapted to the studied problem through a judicious choice of the grid parameters.
Physical Chemistry Chemical Physics 11/2011; 13(42):18738-54. · 3.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: The presence of shape resonances due to tunneling through the centrifugal barrier modifies strongly the dynamics of cold atom scattering. As shown on the example of the ground and lowest triplet electronic states of the 85Rb133Cs molecule, the crucial parameter is, as usual for cold collisions, the scattering length. A general description of shape resonances of diatomic molecules is given from three simple single channel asymptotic models, whose respective performances are discussed. The first model, which consists of a R-6 potential limited at short range by a repulsive wall, positioned to reproduce the s-wave scattering length, accounts satisfactorily for the main system-independent properties of shape resonances. Introduction in the model of energy- and angular-momentum-dependent nodal lines specific to the inner part of the potential greatly improves its efficiency. When the energy and angular momentum dependence of the nodal lines cannot be deduced from full potential calculations or from experiment, a rough, but universal, estimate of these properties is obtained by extending the R-6 behavior of the potential up to the origin.
Physical Review A 07/2010; 82(1). · 3.04 Impact Factor
[show abstract][hide abstract] ABSTRACT: In the polar RbCs molecule, the strong spin-orbit coupling between the A 1Σ+ and b 3Π diabatic electronic states correlated to the Rb(5s)Cs(6p) dissociation limit is at the origin of a global mixing of the two vibrational 0+(P1∕2,3∕2) series coupled radiatively to both X 1Σ+ and a 3Σ+ states. This so-called “resonant coupling” plays a crucial role in the formation of ultracold stable RbCs molecules through photoassociation into 0+ levels followed by stabilization through spontaneous emission. We analyze quantitatively the mechanisms of photoassociation and stabilization through 0+ levels, starting from and leading to either the singlet or the triplet states and we compare the efficiency of the four paths leading to the formation of stable RbCs molecules. Comparison between the two isotopomers 87Rb133Cs and 85Rb133Cs is also reported: the overall process of formation of stable molecules is one order of magnitude larger for 87RbCs. The simple two-channel model presented here yields the general rules for a standard analysis of the effects of resonant coupling between electronic states. To underline the specificity of heteronuclear molecules, the 0+ coupled system of the RbCs molecule is compared to its analog, the 0u+ system of the Rb2 molecule.