Laser-cooling molecules

The Buffer Gas Beam: An Intense, Cold, and Slow Source for Atoms and Molecules

“…The number of re-pump lasers needed to close the optical transition grows accordingly. Despite these challenges, Di Rosa [93] pointed out that a set of molecules with strong single photon transitions and a highly diagonal vibrational transitions (Frank-Condon factors [85]) may be feasible for direct laser cooling. The first criterion ensures a large photon scattering rate, meaning that a sufficient number of photons can be scattered in the limited interaction time (determined by the molecular beam velocity and geometrical constraints on the length of the interaction region).…”

“…Di Rosa [93] listed a few molecules that satisfied the above requirements, including CaH and NH. Most of these molecules can scatter ∼ 100 photons without any vibrational re-pump lasers, and can scatter up to ∼ 10 4 photons with one v = 1 re-pump laser.…”

“…As mentioned earlier (see Table I), a buffer gas cooled beam can deliver higher brightness and lower forward velocity for these types of species. As an example, a boosted buffer gas beam has a typical forward velocity of ∼ 150 m s −1 , which reduces the number of photons needed to stop a CaH molecule by a factor of ∼ 5 compared to a 1300 K oven source, as initially proposed by Di Rosa [93].…”

CaH Rydberg series, oscillator strengths and photoionization cross sections from Molecular Quantum Defect and Dyson Orbital theories

“…Ever since, several bands of CaH have been detected in cool brown dwarfs, where high abundances of this molecule have been recorded [4,5,6]. More recently, the chemical abundance of CaH in Kapteyn's Star [6] and in T dwarfs have been determined [7,8]. Moreover, CaH is thought to be a relevant repository of gas-phase metal atoms [9] because its spectrum is present in a variety of interstellar environments.…”

Continuous all-optical deceleration and single-photon cooling of molecular beams

“…Spontaneous decay processes that lead to "dark states" that are excluded from this cycle are present in most atoms, and are ubiquitous in molecules due to their vibrational degree of freedom. One way to circumvent this issue is to apply more lasers to reconnect these dark states to the cycling transition [16]. This approach was recently demonstrated with carefully chosen molecular species [17][18][19], and shows particular promise as a method to reach the ultracold regime for those species.…”