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Laser cooling and trapping of neutral molecules has made substantial progress in the past few years. On one hand, molecules have more complex energy level structures than atoms, thus bringing great challenges to direct laser cooling and trapping; on the other hand, cold molecules show great advantages in cold molecular collisions and cold chemistry, as well as the applications in many-body interactions and fundamental physics such as searching for fundamental symmetry violations. In recent years, polar diatomic molecules such as SrF, YO, and CaF have been demonstrated experimentally in direct laser cooling techniques and magneto-optic traps (MOTs), all of which require a comprehensive understanding of their molecular internal level structures. Other suitable candidates have also been proposed, such as YbF, MgF, BaF, HgF or even SrOH and YbOH, some of which are already found to play important roles in searching for variations of fundamental constants and the measurement of the electron’s Electric Dipole Moment ( eEDM). As early as 2004, the CaH molecule was selected as a good candidate for laser cooling and magneto-optical trapping. In this article, we first theoretically investigate the Franck−Condon factors of CaH in the
${{\rm{A}}}^{2}\Pi _{1/2}\leftarrow {{\rm{X}}}^{2}\Sigma _{1/2}$ transition by the Morse potential method, the closed-form approximation method and the Rydberg-Klein-Rees method separately, and prove that Franck−Condon factor matrix between$ {\mathrm{X}}^{2}\Sigma _{1/2} $ state and$ {\mathrm{A}}^{2}\Pi _{1/2} $ state is highly diagonalized, and indicate that sum of f 00, f 01and f 02for each molecule is greater than 0.9999 and almost 1 × 10 4photons can be scattered to slow the molecules with merely three lasers. The molecular hyperfine structures of$ {X}^{2}\Sigma _{1/2} $ , as well as the transitions and associated hyperfine branching ratios in the${{\rm{A}}}^{2}\Pi _{1/2}\left(J=1/2, \mathrm{ }+\right)\leftarrow {{\rm{X}}}^{2}\Sigma _{1/2}\left(N=1, \mathrm{ }-\right)$ transition of CaH, are examined via the effective Hamiltonian approach. According to these results, in order to fully cover the hyperfine manifold originating from$ |X, \mathrm{ }N=1, -\rangle $ , we propose the sideband modulation scheme that at least two electro-optic modulators (EOMs) should be required for CaH when detuning within 3 Γof the respective hyperfine transition. In the end, we analyze the Zeeman structures and magnetic gfactors with and without Jmixing of the$ |X, \mathrm{ }N=1, -\rangle $ state to undercover more information about the magneto-optical trapping. Our work here not only demonstrates the feasibility of laser cooling and trapping of CaH, but also illuminates the studies related to spectral analysis in astrophysics, ultracold molecular collisions and fundamental physics such as exploring the fundamental symmetry violations.-
Keywords:
- cold molecules/
- laser cooling/
- CaH molecule/
- Franck-Condon factors
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方法 f00 f01 f02 f11 f13 闭合近似 0.9846 0.0152 0.0001 0.9545 0.00035 莫尔斯势 0.9850 0.0146 0.0004 0.9560 0.0014 RKR反演 0.99542 0.00454 0.00004 0.98631 0.00012 Ref. [50] 0.961 0.038 0.002 0.885 0.005 参数 Ref. [59] $ {B}_{\upsilon } $/MHz 126772.935 $ {D}_{\upsilon } $/MHz 5.546 $ {\gamma_\upsilon } $/MHz 1305.755 $ {b}_{\upsilon } $/MHz 155.785 $ {c}_{\upsilon } $/MHz 4.74 $ N\to N' $ $J \to J'$ $F \to F' $ νcal/MHz νexpa/MHz νcal–νexp/MHz 0$ \to $1 1/2$ \to $1/2 1$ \to $1 252163.0907 252163.082 0.0087 1$ \to $0 252216.3510 252216.347 0.004 0$ \to $1 252320.4557 252320.467 –0.0113 1/2$ \to $3/2 1$ \to $1 254074.8288 254074.834 –0.0052 1$ \to $2 254176.4055 254176.415 –0.0095 0$ \to $1 254232.1938 254232.179 0.0148 aRef. [59] 理想的组分 考虑J混合后真实的组分 $ \left|J=3/2, \right.F=2\rangle $ $ \left|J=3/2, \right.F=2\rangle $ $ \left|J=3/2, \right.F=1\rangle $ $0.999238\left|J=3/2, \right.F=1\rangle +\\0.039028\left|J=1/2, \right.F=1\rangle$ $ \left|J=1/2, \right.F=1\rangle $ $-0.039028\left|J=3/2, \right.F=1\rangle +\\0.999238\left|J=1/2, \right.F=1\rangle$ $ \left|J=1/2, \right.F=0\rangle $ $ \left|J=1/2, \right.F=0\rangle $ J F MF F'= 0 F'= 1 $M'_{\rm F} = 0$ $M'_{\rm F} = -1$ $M'_{\rm F} = 0$ $M'_{\rm F} = 1$ 3/2 –2 0.000000 0.166667 0.000000 0.000000 –1 0.000000 0.083333 0.083333 0.000000 0 0.000000 0.027778 0.111111 0.027778 1 0.000000 0.000000 0.083333 0.083333 2 0.000000 0.000000 0.000000 0.166667 3/2 –1 0.099024 0.034202 0.034202 0.000000 0 0.099024 0.034202 0.000000 0.034202 1 0.099024 0.000000 0.034202 0.034202 1/2 –1 0.234309 0.215798 0.215798 0.000000 0 0.234309 0.215798 0.000000 0.215798 1 0.234309 0.000000 0.215798 0.215798 1/2 0 0.000000 0.222222 0.222222 0.222222 态 g(没有J混合) g(有J混合) $ \left|J=3/2, \right.F=2\rangle $ 0.50 0.50 $ \left|J=3/2, \right.F=1\rangle $ 0.83 0.865 $ \left|J=1/2, \right.F=1\rangle $ –0.33 –0.365 $ \left|J=1/2, \right.F=0\rangle $ 0.00 0.000 -
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