# High-resolution optical spectroscopy with a buffer-gas-cooled beam of BaH molecules

## TL;DR

This paper reports the development of a cryogenic buffer-gas-cooled beam of BaH molecules and high-resolution spectroscopy, advancing the potential for laser cooling and trapping of diatomic hydrides.

## Contribution

The study introduces a new apparatus producing a high-flux, low-velocity BaH molecular beam and provides detailed spectroscopic data relevant to laser cooling.

## Key findings

- Produced a molecular beam with ~10^10 molecules/sr/pulse
- Achieved molecules with velocities below 100 m/s and temperature of 0.1 K
- Measured hyperfine structure and magnetic g-factors in relevant states

## Abstract

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 $\sim1\times10^{10}$ molecules/sr/pulse in the X$^2\Sigma^+$ ($v''=0,N''=1$) state of primary interest. More than $1\times10^7$ 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 $g$ factors in the X$^2\Sigma^+$, B$^2\Sigma^+$, and A$^2\Pi_{1/2}$ states.