Optimizing the photoassociation of cold atoms by use of chirped laser pulses

Abstract

Abstract. Photoassociation of ultracold atoms induced by chirped picosecond pulses is analyzed in a nonperturbative treatment by following the wavepackets dynamics on the ground and excited surfaces. The initial state is described by a Boltzmann distribution of continuum scattering states. The chosen example is photoassociation of cesium atoms at temperature T=54 µK from the a 3 Σ + u (6s, 6s) continuum to bound levels in the external well of the 0 − g (6s + 6p 3/2 ) potential. We study how the modification of the pulse characteristics (carrier frequency, duration, linear chirp rate and intensity) can enhance the number of photoassociated molecules and suggest ways of optimizing the production of stable molecules.

Short-pulse photoassociation in rubidium below theD1line

“…A similar behavior has been reported for cesium in Refs. [14,15]. The focussing effect for a negative chirp compared to a transform-limited pulse is less pronounced than reported in Refs.…”

“…The continuum of scattering states is represented by a finite number of box states [14,15,27]. These box states are normalized to one.…”

“…To obtain the energy normalization which is usually employed for continuum states, they have to be weighted by the density of states of the box (see Ref. [15] for details). The initial state of the calculations is chosen to be the s-wave scattering state with collision energy E coll equivalent to a temperature T = E coll /k B = 105 µK (with k B the Boltzmann constant).…”

“…4 population is transferred only from within the photoassociation window (see Ref. [15] for a detailed discussion). The larger enhancement for 0 + u than for 1 g is explained by the different topology of the potentials leading to different values R c (ω L ).…”

“…In an eigenstate-picture, levels with large vibrational period are excited before those with smaller vibrational period. The chirp can now be chosen to synchronize the excitation of partial wavepackets such that they will all arrive at exactly the same time at the inner classical turning point [14,15]. The value of the chirp can be estimated in terms of the vibrational period and the revival period of the level which is resonant with the central frequency of the pulse, i.e.…”