Absorption spectroscopy for laser cooling and high-fidelity detection of barium monofluoride molecules

TL;DR

This paper uses high-resolution absorption spectroscopy to precisely characterize BaF molecular transitions, improving molecular constants, confirming hyperfine splitting, and demonstrating high-fidelity fluorescence imaging for laser cooling and precision measurements.

Contribution

It provides new spectroscopic data and insights crucial for laser cooling of BaF molecules, enabling high-fidelity detection and potential precision measurement applications.

Findings

Improved molecular constants for 138Ba19F and 136Ba19F

Confirmed hyperfine splitting in excited state

Demonstrated background-free fluorescence imaging

Abstract

Currently, there is great interest in laser cooling of barium monofluoride (BaF) molecules for precision tests of fundamental symmetries. We use high-resolution absorption spectroscopy to characterize several as yet imprecisely known transition frequencies required to realize such cooling. We extract an improved set of molecular constants for the bosonic 138Ba19F and 136Ba19F isotopologues, confirm the existence of a significant hyperfine splitting in the excited state of the laser cooling cycle, and investigate the effects of this splitting on the achievable cooling forces. As a direct application of our spectroscopic insights, we experimentally demonstrate nearly background-free fluorescence imaging of a BaF molecular beam in a glass cell vacuum chamber. We expect such high-fidelity detection to be useful for various types of precision measurement scenarios.