Two-photon photoassociation spectroscopy of an ultracold heteronuclear molecule

Abstract

We report on two-photon photoassociation (PA) spectroscopy of ultracold heteronuclear LiRb molecules. This is used to determine the binding energies of the loosely bound levels of the electronic ground singlet and the lowest triplet states of LiRb. We observe strong two-photon PA lines with power broadened line widths greater than 20 GHz at relatively low laser intensity of 30 W/cm 2 . The implication of this observation on direct atom to molecule conversion using stimulated Raman adiabatic passage (STIRAP) is discussed and the prospect for electronic ground state molecule production is theoretically analyzed. The experiment is performed in a dual-species magnetooptical trap (MOT) apparatus for simultaneous cooling and trapping of 7 Li and 85 Rb atoms, the details of which are described elsewhere [35,36]. The 85 Rb MOT is operated as a dark spot MOT in order to reduce atom loss by light assisted collisions [35,36] and to optically pump 85 Rb atoms to the 5s 2 S 1/2 (F = 2) state. The 7 Li MOT is a traditional MOT where most of the atoms are in the 2s 2 S 1/2 (F = 2) state. The scheme used for Raman-type 2-photon PA spectroscopy is shown in Fig. 1(a). The frequency PA  of the PA laser is tuned to at a PA transition to create LiRb* molecules in a specific bound vibrational level near the Li (2s 2 S 1/2 ) + Rb (5p 2 P 1/2 ) atomic asymptote (* indicates electronically excited states). Molecule production leads to a reduction in the number of atoms trapped in the MOT and a corresponding reduction in atomic fluorescence [10,11]. We show an example of this trap loss signal in Fig. 2(a). With PA  held fixed on a PA resonance, the frequency R  of a second laser, called the Raman laser, is scanned across a bound-bound ↔ transition between the excited and ground electronic states of LiRb. When the frequency R  is resonant with the bound-bound transition, this field strongly couples the two levels and causes shifts (or splitting) in their energies due to a phenomenon commonly known as the Autler-Townes (AT) splitting. Due to the shift in the energy --

Two-photon photoassociation spectroscopy of the Σ+2 YbLi molecular ground state

“…Two-photon PA spectroscopy can be used to probe the interatomic potential of an initially unbound atom pair [21,[23][24][25]. The schematic for the PA process is shown in Figure 1.…”

Beyond-Born-Oppenheimer effects in sub-kHz-precision photoassociation spectroscopy of ytterbium atoms

“…Two-photon processes are also possible: both Raman [19] and Autler-Townes [20,21] laser configurations can be used to measure the positions of ground state energy levels in a process known as two-color photoassociation spectroscopy [22][23][24][25][26]. Photoassociation spectroscopy has also been demonstrated for heteronuclear molecules, for example RbYb [27,28] and LiRb [29]. Due to preferential Franck-Condon factors between ground scattering state and weakly bound excited states, photoassociation spectroscopy is primarily used for the measurements of bound states close to the appropriate dissociation limit.…”

Photoassociation of Ultracold CsYb Molecules and Determination of Interspecies Scattering Lengths

“…Two-photon photoassociation is an extremely useful technique to measure the binding energy of near-threshold vibrational levels. This technique has been applied in a large number of single-species [179,313,329,[348][349][350][351][352][353][354] and two-species ultracold atom experiments [61,297,[355][356][357][358] with considerable success. In addition, pairing of this technique with Autler-Townes spectroscopy allows measurements of the FCFs between electronically excited and ground state vibrational levels.…”