Influence of water vapor on measurements of the refractive index of a surface layer of LiNbO3 layer during high-temperature annealing

An investigation was made of the dependence of the rate of formation of a waveguide layer in lithium niobate on the water vapor concentration in a gaseous medium in which high-temperature annealing took place. The formation of an "antiwaveguide" layer was observed for the first time during annealing of crystals in an atmosphere containing no lithium dioxide vapor. It was also noted that there was an optimal (to suppress outdiffusion) water vapor concentration.