LASER-INDUCED TRANSIENT AND PERMANENT GRATINGS IN EU3-DOPED DUAL ALKALINE-EARTH SILICATE-GLASSES()

We have studied the formation of laser induced permanent and transient refractive index gratings in Eu3+-doped dual alkaline earth silicate glasses. The growth, decay, and erasure of the grating are reported as functions of the write-beam power and crossing angle. The concentrati ons of the alkaline earth modifiers affected the diffraction efficienc y of the induced grating. The diffraction efficiency of the permanent grating decreased as the concentrations of the larger and more massive alkaline earth modifiers (Ca, Sr, Ba) increased. The strength of the transient signal increased with the strength of the permanent grating. The permanent change in the index of refraction was attributed to the migration of small modifiers such as Na and Mg through the glass netw ork. The energy to activate these modifiers was provided by the non-ra diative relaxation of excited Eu3+. The decay of the transient signal was the same as that of the fluorescence of the D-5(0) --> F-7(0) stat es and was independent of the write-beam power. We suggest that the re sults of this research indicate that the use of large alkaline earth m odifiers such as Ca, Sr, and Ba with concentrations less than 2 mol% p roduce a modest improvement in the diffraction efficiency in the rare earth-doped silicate glasses. (C) 1998 Elsevier Science B.V. All right s reserved.