We report heteronuclear photoassociation spectroscopy in a mixture of magneto-optically trapped ${}^6\mathrm{Li}$ and ${}^7\mathrm{Li}.$ The laser-induced decrease in the ${}^7\mathrm{Li}$ steady-state particle number, only appearing in the presence of ${}^6\mathrm{Li},$ gives clear evidence of photoassociation to form ${}^6{\mathrm{Li}}^7\mathrm{Li}.$ Hyperfine resolved spectra of the vibrational level $v=83\mathrm{}$ of the singlet state ${\mathrm{A}}^1{\Sigma }_u^{+}$ have been taken up to intensities of $1000{\mathrm{W}/\mathrm{c}\mathrm{m}}^2.$ 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 $40{\mathrm{W}/\mathrm{c}\mathrm{m}}^2$ can be determined.

• Received 9 October 2002

DOI:https://doi.org/10.1103/PhysRevA.66.061403