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arXiv:2202.02463 · Frontiers of Physics

Saturated absorption spectroscopy of buffer-gas-cooled Barium monofluoride molecules

Wenhao Bu, Yuhe Zhang, Qian Liang, Tao Chen, Bo Yan

Published Sep 12, 2022• 17 citations
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Abstract

We report an experimental investigation on the Doppler-free saturated absorption spectroscopy of buffer-gas-cooled Barium monofluoride (BaF) molecules in a 4 K cryogenic cell. The obtained spectra with a resolution of 19 MHz, much smaller than previously observed in absorption spectroscopy, clearly resolve the hyperfine transitions. Moreover, we use these high-resolution spectra to fit the hyperfine splittings of excited A ( v = 0) state and find the hyperfine splitting of the laser-cooling-relevant A 2 Π 1/2 ( v = 0, J = 1/2,+) state is about 18 MHz, much higher than the previous theoretically predicted value. This provides important missing information for laser cooling of BaF molecules.

DOI
10.1007/s11467-022-1194-x

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Barium monohydride (BaH) is an attractive candidate for extending laser cooling and trapping techniques to diatomic hydrides. The apparatus and high-resolution optical spectroscopy presented here demonstrate progress toward this goal. A cryogenic buffer-gas-cooled molecular beam of BaH was constructed and characterized. Pulsed laser ablation into cryogenic helium buffer gas delivers $\ensuremath{\sim}1\ifmmode\times\else\texttimes\fi{}{10}^{10}$ molecules/sr/pulse in the $X^{2}\mathrm{\ensuremath{\Sigma}}^{+}$ (${v}^{\ensuremath{'}\ensuremath{'}}=0,{N}^{\ensuremath{'}\ensuremath{'}}=1$) state of primary interest. More than $1\ifmmode\times\else\texttimes\fi{}{10}^{7}$ of these molecules per pulse enter the downstream science region with forward velocities below 100 m/s and transverse temperature of 0.1 K. This molecular beam enabled high-resolution optical spectra of BaH in quantum states relevant to laser slowing and cooling. The reported measurements include hyperfine structure and magnetic ggg factors in the $X^{2}\mathrm{\ensuremath{\Sigma}}^{+}$, $B^{2}\mathrm{\ensuremath{\Sigma}}^{+}$, and $A^{2}\mathrm{\ensuremath{\Pi}}_{1/2}$ states.
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