Establishing a nearly closed cycling transition in a polyatomic molecule

TL;DR

This paper demonstrates a near-closed optical cycling transition in CaOH, enabling scattering of around 10,000 photons, which is a significant step towards laser cooling and trapping of this polyatomic molecule.

Contribution

The study provides precise measurements of rovibronic branching ratios and high-resolution spectroscopy, confirming theoretical predictions and identifying decay pathways in CaOH.

Findings

Measured branching ratios with 10^{-4} precision

Observed weak symmetry-forbidden decays to bending modes

Predicted additional decay pathways through calculations

Abstract

We study optical cycling in the polar free radical calcium monohydroxide (CaOH) and establish an experimental path towards scattering $\sim$$10^4$ photons. We report rovibronic branching ratio measurements with precision at the $\sim10^{-4}$ level and observe weak symmetry-forbidden decays to bending modes with non-zero vibrational angular momentum. Calculations are in excellent agreement with these measurements and predict additional decay pathways. Additionally, we perform high-resolution spectroscopy of the $\widetilde{\text{X}}\,^2\Sigma^+(12^00)$ and $\widetilde{\text{X}}\,^2\Sigma^+(12^20)$ hybrid vibrational states of CaOH. These advances establish a path towards radiative slowing, 3D magneto-optical trapping, and sub-Doppler cooling of CaOH.