High-resolution photoassociation spectroscopy of the ${}^6$Li${}_2$ $A\left(1^1{\Sigma }_u^{+}\right)$ state

We present spectroscopic measurements of seven vibrational levels $v=29–35$ of the $A\left(1^1{\Sigma }_u^{+}\right)$ excited state of Li${}_2$ molecules by the photoassociation of a degenerate Fermi gas of ${}^6$Li atoms. The absolute uncertainty of our measurements is $\pm 0.00002$ cm${}^{-1}$ ($\pm 600$ kHz) and we use these new data to further refine an analytic potential for this state. This work provides high accuracy photoassociation resonance locations essential for the eventual high-resolution mapping of the $X\left(1^1{\Sigma }_g^{+}\right)$ state enabling further improvements to the $s$-wave scattering length determination of Li and enabling the eventual creation of ultracold ground-state ${}^6$Li${}_2$ molecules.