Molecular spectroscopy of a Bose-Einstein condensate with attractive interactions

Molecular spectroscopy is used to probe a quantum degenerate gas of 7Li atoms. Several effects are investigated using both single-color and two-color (Raman) photoassociative spectroscopy. An unusual spectral shift with laser intensity is observed for single-color photoassociation and the intensity dependence agrees with theoretical predictions. Additionally, the prospects for altering the interactions between ground-state atoms is investigated for both the single-color and Raman schemes. The single-color scheme is found to be impractical experimentally (although feasible theoretically) while the Raman scheme may be experimentally feasible as well. The Raman spectra display an interesting lineshape which is found to reflect the rate for inelastic collisions involving ground-state molecules (produced via the Raman process) as well as the attractive mean-field interactions between atoms in the condensate. Under certain circumstances, a dispersive Raman lineshape is observed which may be due to coherence properties of both the condensate and the thermal gas. Additionally, the Raman lineshape appears to reflect the kinetic time scale for thermal atoms to enter the condensate via elastic collisions. The Raman technique is applied to studies of the condensate growth and collapse dynamics caused by attractive interactions between condensate atoms, and enables the first direct observations of this phenomenon