We report on the development and application of a parametrized crystal-field model for both
C1 symmetry centers in trivalent erbium-doped
Y2SiO5. High-resolution Zeeman and temperature dependent absorption spectroscopy was performed to acquire the necessary experimental data. The obtained data, in addition to the ground
(4I15/2Z1) state and exited
(4I13/2Y1) state Zeeman and hyperfine structure, were simultaneously fitted in order to refine an existing crystal-field interpretation of the
Er3+:
Y2SiO5 system. We demonstrate that it is possible to account for the electronic, magnetic, and hyperfine structure of the full
4f11 configuration of
Er3+:
Y2SiO5 and further, that it is possible to predict both optical polarization behavior and high magnetic field hyperfine structure of transitions in the $1.5\text{\ensuremath{-}}\ensuremath{\mu}\mathrm{m}$ telecommunications band.
We have developed and demonstrated a scheme to achieve rotationally closed photon cycling in polyatomic molecules with complex hyperfine structure and sensitivity to hadronic symmetry violation, specifically,
171YbOH and
173YbOH. We calculate branching ratios for spontaneous decay into the different hyperfine levels and identify repumping schemes. We demonstrate our scheme by cycling photons in a molecular beam and verify that we have achieved rotationally closed cycling by measuring optical pumping into unaddressed vibrational states. Our work makes progress along the path toward utilizing photon cycling for state preparation, readout, and laser cooling in precision measurements of polyatomic molecules with complex hyperfine structure.
Following the interest in the experimental realization of laser cooling for thallium fluoride (TlF), determining the potential of thallium chloride (TlCl) as a candidate for laser cooling experiments has recently received attention from a theoretical perspective [Yuan et al., J. Chem. Phys. 149, 094306 (2018)]. From these ab initio electronic structure calculations, it appeared that the cooling process, which would proceed from transitions between a3Π0+ and X1Σ0+ states, had as a potential bottleneck the long lifetime (6.04 µs) of the excited state a3Π0+, that would make it very difficult to experimentally control the slowing zone. In this work, we revisit the electronic structure of TlCl by employing four-component Multireference Configuration Interaction (MRCI) and Polarization Propagator (PP) calculations and investigate the effect of such approaches on the computed transition dipole moments between a3Π0+ and a3Π1 excited states of TlCl and TlF (the latter serving as a benchmark between theory and experiment). Whenever possible, MRCI and PP results have been cross-validated by four-component equation of motion coupled-cluster calculations. We find from these different correlated approaches that a coherent picture emerges in which the results of TlF are extremely close to the experimental values, whereas for TlCl the four-component calculations now predict a significantly shorter lifetime (between 109 and 175 ns) for the a3Π0+ than prior estimates. As a consequence, TlCl would exhibit rather different, more favorable cooling dynamics. By numerically calculating the rate equation, we provide evidence that TlCl may have similar cooling capabilities to TlF. Our analysis also indicates the potential advantages of boosting stimulated radiation in optical cycles to improve cooling efficiency.