Influence of the Pretreatment of Lithium Niobate Surface with Plasma and Ultraviolet Radiation on the Proton Exchange in Benzoic Acid Melts

The treatment of lithium niobate surface with argon plasma results in an increase in defect density within the surface layer which affects the process of proton exchange causing the formation of proton-rich phases of the Li
_1-x
H
_x
NbO
₃
solid solution (X cut), the rise in internal stress, and even local dissolution of the surface layer in zones with maximal proton concentration. In the course of subsequent annealing, the characteristics of waveguides in plasma-treated and untreated samples come closer together. The plasma treatment of the surface of Z cut LiNbO
₃
crystal affects the proton exchange to a lesser extent due to smaller strains in the proton-exchange phases. The treatment of lithium niobate surface (X and Z cuts) before proton exchange with ultraviolet radiation (wavelength 172 nm) has only slight effect on the process of proton exchange and the characteristics of obtained waveguides.