Vapor transport equilibration (VTE) in a congruent lithium niobate (LiNbO3) plate is modeled using the implicit finite difference method, and Li-diffusion at 1100 °C in both Z-cut and X-cut plates with thicknesses from 0.5 to 3 mm is simulated for VTE duration up to 450 h. Li-diffusivity at 1100 °C was determined experimentally based upon secondary-ion-mass spectrometry (SIMS) analysis. A good agreement of numerical results with SIMS results or optical absorption edge measurement results confirms the accuracy of the Li-diffusivity and the validity of the VTE model proposed and the numerical method employed. The mutual influence problem of two VTE processes from the top and the bottom surfaces of the plate and the VTE duration needed to fully VTE-treat a plate are discussed in relation to the crystal's cut and thickness. The VTE duration dependence on the mean Li/Nb ratio within a 20 μm depth is studied.

A model is proposed for describing two-dimensional diffusion of Ti into an initially congruent LiNbO3 crystal under a Li-enriched atmosphere created by a mixed two-phase (Li3NbO4 and LiNbO3) powder at elevated temperature [vapor transport equilibration (VTE)]. The influence of VTE treatment on Ti diffusivity is considered in the model. To solve the model, four key input parameters including Li-concentration-dependent Li and Ti diffusivities and two switching times t1 and t2 were determined. Prior to solve the Ti-diffusion model, a one-dimensional VTE model is solved at first to obtain the dynamic Li2O concentration depth profile. Both the Li-diffusion and Ti-diffusion models were solved by using finite difference method. Based on secondary-ion-mass spectrometry analysis, the validity of the VTE and Ti-diffusion models as well as the numerical method employed are confirmed. After that, diffusion at 1100°C of an 8-μm-wide, 100-nm-thick Ti strip defined on the surface of a Z-cut or an X-cut substrate was simulated for the VTE duration up to 130h. Based on the numerical results, the Ti-(Li-)diffusion characteristics are discussed in the aspects of (1) the relation of depth and width profile function of Ti concentration to the VTE duration, (2) the substrate cut effect on both the Ti and Li diffusions, (3) the relation of the 1∕e Ti-concentration depth and half-width to the VTE duration, and (4) the VTE duration dependence of the mean [Li]∕[Nb] ratio within the Ti-diffused layer.

Pun (2005) Light-induced diffraction in thermally reduced congruent and near-stoichiometric Er:LiNbO 3 crystals, Journal of Modern Optics, 52:15, 2105-2126, A polarization-isotropic two-colour light-induced diffraction (LID) phenomenon from thermally reduced congruent and near-stoichiometric Er:LiNbO 3 crystals was observed when these crystals were exposed to superposed 632.8 nm probe and 488 nm pump beams. The LID is characterized by expansion of the probe beam spot and the appearance of alternate bright and dark diffraction rings at higher pump light intensities. This phenomenon is absent not only in all other Er-doped crystals which either were as grown or had experienced other postgrowth treatments such as vapour transport equilibration (VTE), oxidation and strong annealing but also in a pure VTE-treated crystal even though the crystal was subjected to the same reduction procedure. The LID characteristics of five reduced crystals, which have different Li-to-Nb ratios and different doping levels of Er 3þ , were studied in detail by changing the light intensity, polarization state and wave vector direction of both the pump and the probe beams. The origin of the LID was investigated from the viewpoints of the red fluorescence of Er 3þ excited by a 488 nm pump beam, light-induced scattering and light-induced thermal nonlinearity. The results have shown that the thermal nonlinearity mechanism is preferred as it can reasonably explain almost all the observed experimental phenomena.