on the occasion of his 65th birthdayThe technique of two-photon-absorption spectroscopy with polarized laser-light is applied to localized excitations of 4f-electrons in crystals. The relevant selection rules are discussed. A method is outlined for the unique determination of the relative magnitude of partial transition-probabilities with different types of symmetry using linear and circular polarization of the incident light. The anisotropy of the two-photon absorption has been measured in single crystals of cubic CaF,:F,u2+ a t five different wavenunibers. The relative intensities of transitions belonging to the three different types of symmetry active in twophoton absorption are constant in the range of the e-band (26,000 to 29,000 cm-l) but differ from these values at 37,700 cm-l in the range between the e-and the t-band. This result is discussed in the frame of existing interpretations of the 4f65d-configuration of Eu2+ in CaF,.
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