Abstract:
Technological approaches to obtaining nonlinear optical single-crystals of double doping LiNbO$_3$ : B : Gd have been investigated. It is shown that simultaneous doping with boron and gadolinium allows for targeted impact on the defect structure and practical properties of lithium niobate crystals. The solid-phase synthesis-granulation method helped to obtain the initial monophase charge of lithium niobate with a concentration of B$_2$O$_3$ of 0.03 mol.% and Gd$_2$O$_3$ of 0.62 mol.% corresponding to the composition of congruent melting. It has been found that the concentration of boron in the melt after growing LiNbO$_3$ : B : Gd crystals decreases by $\sim$3 times compared to its concentration in the initial charge. Two single crystals LiNbO$_3$:(0.58 $\cdot$ 10$^{-3}$ B$_2$O$_3$) : (0.51 mol.% Gd$_2$O$_3$) and LiNbO$_3$:(0.32 $\cdot$ 10$^{-3}$ B$_2$O$_3$) : (0.53 mol.% Gd$_2$O$_3$) were grown from a melt by the Czochralski method. Single crystals are similar in composition, and they are characterized by a low photorefractive effect, high compositional and optical uniformity. Both LiNbO$_3$ : B : Gd crystals are characterized by high Curie temperatures (1210 and 1213$^\circ$C). Using the method of IR absorption spectroscopy in the region of stretching vibrations of OH groups, it was shown that the increase in the concentration of hydroxyl groups in LiNbO$_3$ : B : Gd crystals is due to physicochemical and technological factors. Using laser conoscopy, it has been shown that the LiNbO$_3$:(0.32 $\cdot$ 10$^{-3}$ B$_2$O$_3$) : (0.53 mol.% Gd$_2$O$_3$) crystal has higher optical uniformity compared to the LiNbO$_3$:(0.58 $\cdot$ 10$^{-3}$ B$_2$O$_3$) : (0.51 mol.% Gd$_2$O$_3$) crystal.
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