Investigation of Zeeman second-order effects in Pr3+:LaCl3using the fluorescence-line-narrowing technique

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Abstract
A technique involving the laser-induced narrowing of a fluorescence line is used to obtain high-resolution spectra of Pr3+:LaCl3. The second-order effects caused by Zeeman and nuclear interactions are systematically investigated in the 3H4E2 to or from 1D2A1 transition. A non-zero perpendicular Zeeman splitting of the ground level, proportional to the square of the magnetic field, is measured and interpreted as being caused by the perturbation by the four upper Stark levels belonging to the 3H4 multiplet. The variation of the number and of the relative intensities of the hyperfine lines is demonstrated to be closely related to the angle between the external magnetic field direction and the crystal axis. It is unambiguously attributed to an angular dependence, with regard to the magnetic field direction, of the hyperfine states of the excited level. The importance of the effect, caused by a very distant perturbing level, is shown to be a result of the quasidegeneracy of the mu =0 excited level.