Title: Transverse Laser Cooling of Calcium Monohydride Molecules
Description: In this thesis, I demonstrate Doppler and Sisyphus cooling of a cryogenic buffer-gas beam of CaH molecules. I detail the construction and optimization of the experimental apparatus, including the cryogenic source, laser systems, vacuum systems and detection schemes. I demonstrate that the cryogenic source produces a bright and slow beam of CaH molecules via ablation of a solid chemical target and thermalization with a He buffer gas. The molecular beam exits the ablation cell with an average forward velocity of 250 ±200 m/s and a molecular beam flux per ablation pulse of ≈ 1×1010 per steradian per pulse. I present the spectroscopic determination of the molecular transitions necessary to pursue laser cooling. These include the X2Σ+ → A2Π1/2 and the X2Σ+ → B2Σ+ transitions that each contain two spin-rotation states, J = 1/2 and J = 3/2, and a further pair of hyperfine states, F = 0,1 and F = 1,2, respectively. Finally, I describe the vibrational repumping transitions between the four hyperfine states of the J = 1/2 and J = 3/2 branches of the V = 1 vibrational state back to the ground state via decay from an intermediary state, X2Σ+(V = 1) → B2Σ+(V = 0) → X2Σ+(V = 0).

I present measurements of the vibrational decay probabilities from the B2Σ+(V = 0) and A2Π1/2(V = 0) excited states to the V = 0,1 and 2 states of the ground X2Σ+ state. Next, I show that we can achieve a high scattering rate of ≈ 1.6E6 photons/second while cycling on the X2Σ+ → A2Π1/2 transition. Finally, I demonstrate the ability to perform transverse cooling of a beam of CaH molecules through both the Doppler mechanism and magnetically assisted Sisyphus mechanism. With the help of a transverse standing wave of laser light, I show that we are able to lower the molecular beam’s transverse temperature from 12.2±1.2 mK to 5.7±1.1mK. This thesis represents a promising start to laser slowing and magneto-optical trapping of CaH molecules, which could provide trapped ultracold samples of atomic hydrogen upon dissociation of the trapped CaH molecules.