58 research outputs found
Features of Molecular Structure Beneficial for Optical Pumping
Fast and efficient state preparation of molecules can be accomplished by
optical pumping. Molecular structure that most obviously facilitates cycling
involves a strong electronic transition, with favorable vibrational branching
(diagonal Franck-Condon factors, aka FCFs) and without any intervening
electronic states. Here, we propose important adjustments to those criteria,
based on our experience optically pumping SiO. Specifically, the preference
for no intervening electronic states should be revised, and over-reliance on
FCFs can miss important features. The intervening electronic state in SiOis
actually found to be beneficial in ground rotational state preparation, by
providing a pathway for population to undergo a parity flip. This contribution
demonstrates the possibility that decay through intervening states may help
state preparation of non-diagonal or polyatomic molecules. We also expand upon
the definition of favorable branching. In SiO, we find that the
off-diagonal FCFs fail to reflect the vibrational heating versus cooling rates.
Since the branching rates are determined by transition dipole moments (TDMs) we
introduce a simple model to approximate the TDMs for off-diagonal decays. We
find that two terms, set primarily by the slope of the dipole moment function
() and offset in equilibrium bond lengths (),
can add (subtract) to increase (decrease) the magnitude of a given TDM.
Applying the model to SiO, we find there is a fortuitous cancellation,
where decay leading to vibrational excitation is reduced, causing optical
cycling to lead naturally to vibrational cooling
Optical Pumping of TeH+: Implications for the Search for Varying mp/me
Molecular overtone transitions provide optical frequency transitions
sensitive to variation in the proton-to-electron mass ratio (). However, robust molecular state preparation presents a challenge
critical for achieving high precision. Here, we characterize infrared and
optical-frequency broadband laser cooling schemes for TeH, a species with
multiple electronic transitions amenable to sustained laser control. Using rate
equations to simulate laser cooling population dynamics, we estimate the
fractional sensitivity to attainable using TeH. We find that laser
cooling of TeH can lead to significant improvements on current
variation limits
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