On the influence of a technological mask on the ionic boundary layer in molten benzoic acid in channel waveguides production

Abstract

This work is devoted to a theoretical study of the influence that a technological mask covering a portion of the surface of a lithium niobate crystal has on the ion boundary layer formed near it in a benzoic acid melt. During proton exchange, lithium ions and benzoate ions enter the melt from the clean surface of the crystal. Their diffusion, electromigration, and recombination are described using transport equations. The electric field generated by the difference in ion concentrations was determined using the electrostatic equation. Calculations have shown that the presence of the mask partially limits the direction of ion transport in the melt. Specifically, an impermeable mask with a relatively large thickness prevents ions from actively propagating longitudinally to the crystal. A significant part of the ions recombine within the cavity formed by the mask walls and the crystal surface. Only a small part of the ions manage to leave this region before recombination. In this case, the concentration distributions are uniform, with a good degree of accuracy, along the surface of the lithium niobate plate. Furthermore, the active propagation of ions into the melt is prevented by the electric field generated near the crystal. Reducing the mask thickness results in some of the ions, as they move away from the crystal, escaping the region bounded by the mask walls. This results in concentration distributions taking a more complex shape. Specifically, as the mask size decreases, the sparse region in the center of the cavity becomes increasingly visible in the benzoate ion distribution.