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It is studied that influence of Li vapor transport equilibration (VTE) on surface refractive index of congruent Mg (4.5 mol%):LiNbO3 crystal at wavelength of 1536 nm. The results show the ordinary index no decreases when t < 40 h, then recoveries slightly and tends to a constant when t >100 h. The extraordinary index ne has the VTE effects as similar as no, but the alteration amplitude is smaller than no. The secondary ion mass spectrometry) study shows that the VTE induces Mg diffusion within the crystal in an inhomogeneous Mg depth profile, depending on the VTE duration. The neutron activation analysis shows that the VTE hardly induces Mg evaporation away from the crystal. First, the Mg ions of crystal internal diffused to the surface in the early stage of VTE, and then they diffused slowly back into the bulk of the crystal toward equilibrium when Li concentration tends to equilibrium.

Abstract

Abstract

Abstract

Abstract

Refractive indices of congruent LiNbO_3 crystals codoped with 0.5 mol% Er_2O_3 and 0-5.0 mol% MgO were measured at room temperature in a wavelength range from 473 to 1536 nm using critical angle measurement and minimum deviation methods. For reference, measurements by the critical angle method were also performed on a congruent LiNbO_3 and a congruent MgO (5 mol%):LiNbO_3. The measured data are compared with previously reported theoretical and/or experimental results of pure and MgO-doped LiNbO_3, especially with the results predicted by the MgO content-related Sellmeier equation (SE) reported by Schlarb and Betzler. It is shown that the Schlarb and Betzler SE consistently predicts a lower index, by as much as 4×10^−3, than what is actually measured by the authors for both congruent LiNbO_3 and for MgO:LiNbO_3, whether it is codoped with Er or not. To check the Er doping effect, measurements by the critical angle method were also performed on some congruent LiNbO_3 crystals singly doped with 0-1.0 mol% Er_2O_3. The results show that Er doping has no measurable effect. It is concluded that there may be a systematic error as one uses the Schlarb and Betzler SE to predict the index of the undoped, only MgO-doped, and Er/Mg-codoped crystals. The Schlarb and Betzler SE parameters are refined to fit our experimental data. The corrected version of the SE suitable for MgO:LiNbO_3 with or without Er doping is given.