Determination of CaOH and CaOCH${}_3$ vibrational branching ratios for direct laser cooling and trapping

Abstract

Alkaline earth monoalkoxide free radicals (MORs) have molecular properties conducive to direct laser cooling to sub-millikelvin temperatures. Using dispersed laser induced fluorescence (DLIF) measurements from a pulsed supersonic molecular beam source we determine vibrational branching ratios and Franck-Condon factors for the MORs CaOH and CaOCH${}_3$. With narrow linewidth continuous-wave dye laser excitation, we precisely measure fluorescence branching for both $\tilde{X}-\tilde{A}$ and $\tilde{X}-\tilde{B}$ electronic systems in each molecule. Weak symmetry-forbidden decays to excited bending states with non-zero vibrational angular momentum are observed. Normal mode theoretical analysis combined with ab initio structural calculations are performed and compared to experimental results. Our measurements and analysis pave the way for direct laser cooling of these (and other) complex nonlinear polyatomic molecules. We also describe a possible approach to laser cooling and trapping of molecules with fewer symmetries like chiral species.

to be submitted to New Journal of Physics

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• Bichromatic Imaging of Single Molecules in an Optical Tweezer Array
• ExoMol line lists -- XLVII. Rovibronic molecular line list of the calcium monohydroxide radical (CaOH)
• Intensity-borrowing mechanisms pertinent to laser cooling of linear polyatomic molecules
• MARVEL analysis of the measured high-resolution rovibronic spectra of the calcium monohydroxide radical (CaOH)
• Interactions of benzene, naphthalene, and azulene with alkali-metal and alkaline-earth-metal atoms for ultracold studies
• Rotating and vibrating symmetric top molecule RaOCH${}_3$ in the fundamental $\mathcal{P}$, $\mathcal{T}$-violation searches
• Multivalent optical cycling centers in polyatomic molecules
• Vibrational Branching Ratios for Laser-Cooling of Nonlinear Strontium-Containing Molecules
• Theoretical rovibronic spectroscopy of the calcium monohydroxide radical (CaOH)
• Low-$J$ transitions in ${\tilde{A}}^2\Pi (0,0,0)-{\tilde{X}}^2{\Sigma }^{+}(0,0,0)$ band of buffer-gas-cooled CaOH
• Spectroscopy of laser cooling transitions in MgF
• $\mathcal{P}$, $\mathcal{T}$-violating axion-mediated interactions in RaOH molecule