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

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 ~1×10¹⁰ molecules/sr/pulse in the X²Σ⁺ (v^''=0,N^''=1) state of primary interest. More than 1×10⁷ 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 X²Σ⁺, B²Σ⁺, and A²Π1/2 states.