Electron-phonon coupling effects on Yb³⁺spectra in several laser crystals

Abstract

The complex absorption spectra of Yb3+ in YAG, LiNbO3 and YLF, three important laser crystals, are analysed in terms of electron-phonon coupling effects. The local symmetry for Yb3+ in these crystals is noncentrosymmetric allowing the coexistence of several electron-phonon coupling mechanisms in the formation of vibronic spectra. The shape of several Yb3+ absorption lines is interpreted in terms of the near resonant electron-phonon coupling theory. The computer modelling, by taking into account more phonons in the resonance region enables the assignment of crystal-field levels of the Yb3+ 2F5/2 multiplet and an estimation of electron-phonon coupling strengths. The phonons involved in the near resonance processes were observed in Raman spectra too. For YAG the modelling with a phonon density with four peaks in the near resonant region is made and it gives a good description of the complex experimental pattern. In the case of Yb3+ in LiNbO3 and YLF the use of polarization data evidences also the symmetry characteristics of the electron-phonon coupling.