2-PULSE PHOTON-ECHO STUDIES OF OPTICAL DEPHASING IN CAF2-EU2+

Two-pulse photon echo signals are observed for the 4f(7) --> 4f(6)5d t ransition of Eu2+ ions in CaF2. It is believed that these are the firs t coherent transient measurements on an f --> d transition. The echo d ecay is studied as a function of Eu2+ concentration, temperature and m agnetic field. For T = 1.5 K and H = 30 kG, we find T-2 = 40 ns for bo th 0.01% and 0.001% Eu2+ concentrations, indicating that Eu-Eu interac tions are not dominant. T-2 is determined by a combination involving t he electron-phonon direct process coupling the excited state spin leve ls and the Eu-F superhyperfine interaction. Comparison with other rare -earth systems indicates that the electron-phonon coupling in the T, e xcited state has matrix elements that are at least an order of magnitu de stronger. (C) 1998 Elsevier Science B.V. All rights reserved.