  We report heteronuclear photoassociation spectroscopy in a mixture of
magneto-optically trapped 6Li and 7Li. Hyperfine resolved spectra of the
vibrational level v=83 of the singlet state have been taken up to intensities
of 1000 W/cm^2. 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 W/cm^2 can be determined.
