UCLA

Cold molecules represent a frontier in the field of physics. Optical cycling, a process allowing repeated absorption and emission of photons by a molecule without altering its internal state, is the key to trapping and cooling molecules, as well as to quantum manipulation. However, the search for these molecules faces challenges including identifying suitable species that exhibit the required closed transition pathways for efficient optical cycling. The complexity of molecular structures, such as the electronic, vibrational and rotational properties, presents substantial hurdles in advancing this domain. To better understand these molecular physical and chemical properties, we have been working on the optical cycling properties of many different molecules, ranging from diatomic molecular ions to large neutral molecules with mass >300 amu. The results suggest that many of these candidates could potentially be laser-cooled using just a few repumping lasers, although significant progress is still required.

This dissertation focuses on the search of optical cycling molecules by presenting comprehensive studies of a diatomic molecular ion (SiO+) and molecules with optical cycling centers (OCCs). Through detailed analysis utilizing molecular Hamiltonian and experimental approaches such as high-resolution laser spectroscopy and dispersed laser-induced fluorescence (DLIF) spectroscopy, we studied the key mechanisms underlying these molecules. This work elucidates the electronic, vibrational, and rotational structures essential for achieving efficient optical cycling, investigates how the non-Born-Oppenheimer (non-BO) effects, such as the Fermi resonance and Jahn-Teller effects, may affect the cycling properties. The findings of new molecular species, such as the large molecules like Ca/SrOPh-diadamantanes, offer new insights into the selection criteria for potential molecules. Our findings not only enriched the promising molecular systems for laser cooling and quantum state detection, but also provides a foundation for future exploration and application of these molecules in advancing quantum technologies and precision spectroscopy.