Saturation in heteronuclear photoassociation of ⁶Li⁷Li

We report heteronuclear photoassociation spectroscopy in a mixture of magneto-optically trapped ⁶Li and ⁷Li. The laser-induced decrease in the ⁷Li steady-state particle number, only appearing in the presence of ⁶Li, gives clear evidence of photoassociation to form ⁶Li⁷Li. Hyperfine resolved spectra of the vibrational level v=83 of the singlet state A¹Σ_u⁺ have been taken up to intensities of 1000W/cm². The absolute resonance frequencies and the rotational constant have been measured. Saturation of the photoassociation rate has been observed for two hyperfine transitions, which can be shown to be due to saturation of the rate coefficient near the unitarity limit. Saturation intensities on the order of 40W/cm² can be determined.