Light forces in ultracold photoassociation

Abstract

We study the time-resolved photoassociation of ultracold sodium in an optical dipole trap. The photoassociation laser excites pairs of atoms to molecular states of large total angular momentum at high intensities (above 20 kW/cm 2 ). Such transitions are generally suppressed at ultracold temperatures by the centrifugal barriers for high partial waves. Time-resolved ionization measurements reveal that the atoms are accelerated by the dipole potential of the photoassociation beam. We change the collision energy by varying the potential depth, and observe a strong variation of the photoassociation rate. These results demonstrate the important role of light forces in cw photoassociation at high intensities.

Photoassociation to the21Σg+state in ultracold85RbBellos1, Carollo2, Rahmlow3 et al. 2012Phys. Rev. A

“…Unusually high rotational levels, due to mechanisms other than a shape resonance, have been observed by other groups and explained in terms of attraction caused by the trapping laser [40], and attraction caused by dipole trapping from a highly focused PA beam [41]. We do not see evidence for these effects in our work, which as we describe, in this section and the following, is fully accounted for by the shape resonance.…”

Manipulating Higher Partial-Wave Atom-Atom Interactions by Strong Photoassociative Coupling

“…For numerical illustration, we consider a model system of two cold ground state Na atoms coupled to v = 48 vibrational state of 1 g molecular potential by a laser field. Recently, several (up to J = 6) sharp rotational lines of this vibrational state have been observed in PA spectra with a strong laser field [16]. The outer turning point of the excited v = 48, J = 1 level lies inside the centrifugal barrier of ℓ = 0 of the ground continuum.…”

Rotational excitations in two-color photoassociation

“…For numerical illustration, we consider a model system of two cold ground-state (S 1/2 ) 23 Na atoms undergoing PA transition from ground state 3 + u to the vibrational state v = 48 of the excited molecular 1 g state [23]. At large internuclear distance this 1 g potential correlates to 2 S 1/2 + 2 P 3/2 free atoms and at short range to 1 1 g Born-Oppenheimer potential.…”

“…Molecules created by one-or two-color PA of ultracold atoms generally possess low-lying rotational levels J ≤ 3. Motivated by recent experimental observation of excitation of higher rotational states in ultracold PA with an intense laser field [23], we here expore theoretically the possibility of rotational excitations in two-color PA. This may be important for producing translationally cold molecules in selective higher rotational states.…”