Intensity effects in ultracold photoassociation line shapes

We derive ultracold atom-atom photoassociation line shapes valid for intense light fields and investigate laser power effects in sodium and rubidium photoassociation to the purely long-range 0_g^- symmetry state. We consider intensities up to a few hundreds W/cm², a strongly saturating intensity for typical transitions of experimental interest. For these intensities the 0_g^- rotational spectrum is still well resolved; however, it is essential to couple the photoassociation resonance to both s- and d-wave ground-state channels. A low-energy d-wave shape resonance can have a profound effect on the line shape. Understanding the line shape is essential for precision spectroscopic analysis and could improve the extraction of ground-state scattering properties such as scattering lengths.