For laser-cooling considerations, we have theoretically investigated the electronic, rovibrational, and hyperfine structures of the BaF molecule. The highly diagonal Franck-Condon factors and the branching ratios for all possible transitions within the lowest-lying four electronic states have also been calculated. Meanwhile, the mixing between the metastable ${A}^{{\ensuremath{'}}^{2}}\mathrm{\ensuremath{\Delta}}$ and ${A}^{2}\mathrm{\ensuremath{\Pi}}$ states and, further, the lifetime of the $\mathrm{\ensuremath{\Delta}}$ state have been estimated since the loss procedure via the $\mathrm{\ensuremath{\Delta}}$ state might fatally break the main quasicycling $\mathrm{\ensuremath{\Sigma}}\ensuremath{-}\mathrm{\ensuremath{\Pi}}$ transition for cooling and trapping. The resultant hyperfine splittings of each rovibrational state in the ${X}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}$ state provide benchmarks for sideband modulations of the cooling and repumping lasers and the remixing microwaves to address all necessary levels. The calculated Zeeman shift and
g factors for both
X and
A states serve as benchmarks for selection of the trapping laser polarizations. Our study paves the way for future laser cooling and magneto-optical trapping of the BaF molecule.
More recently, laser cooling of the diatomic radical magnesium monofluoride (
24Mg19F) is being experimentally preformed [Appl. Phys. Express 8, 092701 (2015) and Opt. Express 22, 28645 (2014)] and was also studied theoretically [Phys. Rev. A 91, 042511 (2015)]. However, some important problems still remain unsolved, so, in our paper, we perform further theoretical study for the feasibility of laser cooling and trapping the
24Mg19F molecule. At first, the highly diagonal Franck-Condon factors of the main transitions are verified by the closed-form approximation, Morse approximation, and Rydberg-Klein-Rees inversion methods, respectively. Afterwards, we investigate the lower $X{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{1/2}^{+}$ hyperfine manifolds using a quantum effective Hamiltonian approach and obtain the zero-field hyperfine spectrum with an accuracy of less than 30 $\mathrm{kHz}\phantom{\rule{0.16em}{0ex}}\ensuremath{\sim}5\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\text{K}$ compared with the experimental results, and then find out that one cooling beam and one or two repumping beams with their first-order sidebands are enough to implement an efficient laser slowing and cooling of
24Mg19F. Meanwhile, we also calculate the accurate hyperfine structure magnetic
g factors of the rotational state ($X{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{1/2}^{+},N=1$) and briefly discuss the influence of the external fields on the hyperfine structure of
24Mg19F as well as its possibility of preparing three-dimensional magneto-optical trapping. Finally we give an explanation for the difference between the Stark and Zeeman effects from the perspective of parity and time reversal symmetry. Our study shows that, besides appropriate excitation wavelengths, the short lifetime for the first excited state $A{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Pi}}}_{1/2}$, and lighter mass, the
24Mg19F radical could be a good candidate molecule amenable to laser cooling and magneto-optical trapping.
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 $X{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}({v}^{\ensuremath{''}}=0,1)\ensuremath{\rightarrow}A{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Pi}}}_{1/2}({v}^{\ensuremath{'}}=0)$, $X{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}({v}^{\ensuremath{''}}=1,2)\ensuremath{\rightarrow}A{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Pi}}}_{1/2}({v}^{\ensuremath{'}}=1)$, and $X{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}({v}^{\ensuremath{''}}=1)\ensuremath{\rightarrow}B{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}({v}^{\ensuremath{'}}=0)$ bands of MgF. The measured $X{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}({v}^{\ensuremath{''}}=1)\ensuremath{\rightarrow}B{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}({v}^{\ensuremath{'}}=0)$ spectrum allows the spin-rotation and hyperfine parameters of the $B{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}(v=0)$ state of MgF to be determined. Furthermore, we demonstrate optical cycling in MgF by pumping molecules into the $X{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}(v=1,2)$ states. Optical pumping enhances the spectroscopic signals of transitions originating in the ${N}^{\ensuremath{''}}=1$ level of the $X{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}({v}^{\ensuremath{''}}=1,2)$ states.
Nine doublet Λ-S states of calcium monochloride (CaCl) are calculated using the internally contracted multireference configuration interaction method with the Davidson correction. Both the core subvalence and spin-orbit coupling effects are taken into account. Laser cooling of CaCl and production of ultracold chlorine atoms are investigated and assessed. Our computed spectroscopic constants and radiative lifetimes match the available experimental data very well. The determined Franck-Condon factors and vibrational branching ratios of the A(2)Π1/2(ν('))←X(2)Σ1/2 (+)(ν) transition are highly diagonally distributed and the evaluated radiative lifetime for the A(2)Π1/2(ν' = 0) state is 28.2 ns, which is short enough for rapid laser cooling. Subsequently, detection of cold molecules via resonance enhanced multiphoton ionization to determine the final quantum state populations is discussed and the ionization energy calculated. A multi-pulse excitation scheme is proposed for producing ultracold chlorine atoms from zero-energy photodissociation of the cooled CaCl. Our results demonstrate the possibility of producing ultracold CaCl molecules and Cl atoms.