Investigation Of The B³Σ⁺, V=0 State In Aluminium Monofluoride

The aluminium monofluoride (AlF) molecule is a promising candidate for laser cooling and trapping experiments\footnote{Truppe et al., Phys. Rev. A 100, 052513 (2019)}.\\ Here, we describe experiments studying the hyperfine structure of the $b^3\Sigma^+, v=0$ state\footnote{Doppelbauer et al., Mol. Phys. 119:1-2, e1810351 (2020)}. We first determined its radiative lifetime in a pulsed excitation – delayed ionization scheme and measured the rotational structure using (1+2)-REMPI.\\ We recorded laser-induced fluorescence spectra of the $b^3\Sigma^+, v'=0 \leftarrow X^1\Sigma^+, v''=1$ transition of AlF molecules from a bright buffer gas source. The fluorescence detection works background-free because visible photons are emitted after UV excitation. From the obtained line positions, we determined the relevant fine- and hyperfine structure parameters. In a next step, laser-induced fluorescence spectra were recorded after excitation on the $b^3\Sigma^+, v'=0 \leftarrow a^3\Pi_{\Omega}, v''=0$ transition; we use all three spin-orbit ($\Omega=0,1,2$) manifolds of the $a^3\Pi$ state. These spectra were used to improve the uncertainty of our previous measurement of the spin-orbit coupling parameters in the $a^3\Pi, v=0$ state by almost two orders of magnitude.\\ We observed the $b^3\Sigma^+, v'=0 \rightarrow X^1\Sigma^+, v''$ bands, which are result of the spin–orbit coupling of the $b^3\Sigma^+, v=0$ state with the nearby $A^1\Pi$ state