Spectroscopy of laser-cooling transitions in MgF

We measure the complete set of transition frequencies necessary to laser cool and trap MgF molecules. Specifically, we report the frequency of multiple low-J transitions of the $X{{{0.16em}{0ex}}}²{{{Σ}}}⁺({v}^{{''}}=0,1){→}A{{{0.16em}{0ex}}}²{{{Π}}}1/2({v}^{{'}}=0)$, $X{{{0.16em}{0ex}}}²{{{Σ}}}⁺({v}^{{''}}=1,2){→}A{{{0.16em}{0ex}}}²{{{Π}}}1/2({v}^{{'}}=1)$, and $X{{{0.16em}{0ex}}}²{{{Σ}}}⁺({v}^{{''}}=1){→}B{{{0.16em}{0ex}}}²{{{Σ}}}⁺({v}^{{'}}=0)$ bands of MgF. The measured $X{{{0.16em}{0ex}}}²{{{Σ}}}⁺({v}^{{''}}=1){→}B{{{0.16em}{0ex}}}²{{{Σ}}}⁺({v}^{{'}}=0)$ spectrum allows the spin-rotation and hyperfine parameters of the $B{{{0.16em}{0ex}}}²{{{Σ}}}⁺(v=0)$ state of MgF to be determined. Furthermore, we demonstrate optical cycling in MgF by pumping molecules into the $X{{{0.16em}{0ex}}}²{{{Σ}}}⁺(v=1,2)$ states. Optical pumping enhances the spectroscopic signals of transitions originating in the ${N}^{{''}}=1$ level of the $X{{{0.16em}{0ex}}}²{{{Σ}}}⁺({v}^{{''}}=1,2)$ states.