Determine crystal-field dipole orientations and relative phase

Determine the dipole orientations and relative phase of the two electric-dipole transitions connecting the charge-transfer state to the selected Yb3+ crystal-field levels in YbAlO3, thereby fixing the material-specific orientation factor in the reverse-parametric-fluorescence production amplitude.

Background

The benchmark source uses Yb3+ ions in YbAlO3 and models the two optical couplings through an effective charge-transfer state. The production amplitude depends not only on the magnitudes of the two transition dipoles but also on their orientations relative to the pump polarizations and on their relative phase.

The paper introduces an orientation factor |η| and adopts the optimistic value |η|=1 because the relevant crystal-field-resolved dipole data are unavailable. Resolving these quantities through polarization-resolved spectroscopy or first-principles calculations is necessary to replace the optimistic estimate with a material-specific prediction.