Влияние способа сильного легирования на композиционную однородность и оптические свойства монокристаллов LiNbO-=SUB=-3-=/SUB=- : Mg

Raman spectroscopy, laser conoscopy and photoinduced light scattering methods have been applied to comparatively study composition uniformity of strongly doped LiNbO3 crystals with a magnesium concentration close to a threshold value ≈5 mol% MgО, grown from a charge synthesized using precursor Nb2O5:Mg (homogeneous doping method) and at direct addition of magnesium to the melt (direct doping method). It has been shown that application of homogeneous doping method allows one to obtain compositionally more homogeneous heavily doped LiNbO3:Mg crystal than direct melt doping method.

INFLUENCE OF THE METHOD OF DOPING ON UNIFORMITY AND OPTICAL PROPERTIES OF LiNbO:Mg CRYSTALS

Представлены результаты сравнительных комплексных исследований методами спектроскопии комбинационного рассеяния света и лазерной коноскопии композиционной однородности и некоторых оптических свойства близких по составу сильно легированных монодоменизированных кристаллов LiNbO: Mg (5,03 мол. % MgO и LiNbO: Mg (4,75 мол. % MgO), с концентрацией магния, близкой к пороговому значению ≈ 5 мол. % MgO, выращенных из шихты, синтезированной с использованием прекурсора NbO : Mg (метод гомогенного легирования), а также выращенных при непосредственном добавлении магния в расплав (метод прямого легирования). Показано, что методом гомогенного легирования с использованием прекурсора NbO : Mg можно получать отличающиеся низким коэрцитивным полем более композиционно однородные сильно легированные монокристаллы LiNbO : Mg, чем методом прямого легирования расплава магнием. При этом более однородное распределение легирующей добавки в кристаллах гомогенного легирования начинает формироваться уже на стадии синтеза прекурсора NbO : Mg и шихты ниобата лития при формировании химически активных комплексов, определяющих преимущественно кислородно-октаэдрическую структуру прекурсора NbO : Mg. The paper considers results for strongly doped turned to a single domain state crystals LiNbO: Mg (5,03 mol % MgO and LiNbO: Mg (4,75 mol % MgO). Magnesium concentration in these crystals is close to each other and to threshold ≈ 5 mol % MgO . Crystals were grown from a charge synthesized using precursor LiNbO: Mg (homogeneous doping method) and from a charge obtained at a direct addition of magnesium to the charge (direct doping method). Complex studies were carried out by Raman spectroscopy and laser conoscopy. Compositional homogeneity and some optical properties of studied crystals are considered. Homogeneous doping with precursor NbO: Mg method allows us to obtain heavily doped LiNbO: Mg single crystals with low coercive field and more compositionally homogeneous than method of direct melt doping with magnesium. In this case, a more uniform distribution of the dopant in homogeneously doped crystals begins to form at the stage of NbO: Mg precursor synthesis during the formation of chemically active complexes that predominantly determine the oxygen-octahedral structure of the NbO: Mg precursor.

Visualization of the Effect of an Impurity on the Optical Homogeneity of Lithium Niobate Doped with Boron Cations

The laser conoscopy method confirms the high optical uniformity of LiNbO3:B crystals in the range of B2O3 concentrations from 0.008 to 1.24 mol. %. Minor signs of anomalous optical biaxiality appear in the conoscopic patterns of crystals at boron concentrations of 0.12 and 0.83 mol. % at a laser power of 90 mW. The maximum value of the angle of anomalous optical axes for the studied samples is 2V = 10 ́ for the sample (0.12 mol. %), аnd the value of anomalous birefringence corresponds to ∆n = 0.02·10-5.

Structural particularities and optical properties of lithium niobate single crystals grown from the charge doped by boron.

The analysis of structural particularities and optical properties of LiNbO3 : B (0,55, 0,69 and 0,83 mol. % B2O3) was performed by methods of Raman and photoinduced light scattering, infrared absorption and laser conoscopy. It has been established that the boron impurity brings to 1 the distribution coefficient of lithium and niobium in the growing process. Thus, LiNbO3: B crystals grown from a congruent melt approach the stoichiometric crystals in ordering the structural units of the cation sublattice and the Li / Nb ratio.

Visualization of Optical Uniformity Alloyed Single Crystals of Lithium Niobate

It was shown that laser conoscopy can visually detect even slight changes in the optical characteristics of a crystal when it is doped. It has been found that the defective structure of LiNbO3:Zn (4.5 mol. %), LiNbO3:Mg (3.0–5.5 mol.%) crystals associated with an uneven entry of an impurity leads to a local change in the elastic characteristics of the crystal and the appearance of mechanical stresses that distort the conoscopic patterns. This can be an abnormal optical biaxiality, which manifests itself in the form of a rupture and enlightenment of the "Maltese cross" in the center of the conoscopic crystal pattern, or local birefringent inclusions that are recorded as additional interference patterns against the background of the main conoscopic pattern, both in the center of the field of view and in its peripheral area.

Control of Optical Homogeneity of Lithium Niobate Crystals with Admixtures of Rare-Earth Elements Gd, Er by Laser Conoscopy

Interference patterns of single crystals of LiNbO3:Gd, LiNbO3:Er, obtained by laser conoscopy, allow us to estimate the optical homogeneity of the samples under study. The observation of conoscopic patterns of the LiNbO3:Gd single crystal shows that with an increase in the percentage impurity concentration, the anomalous biaxiality in these samples manifests itself to a much greater degree. Anomalous biaxiality for the sample LiNbO3:Er [3.60 wt.%] is present at almost every point of the entrance face, which is manifested in conoscopic patterns in the form of enlightenment and rupture of the “Maltese cross”, which corresponds to the angle 2V~1° between the anomalous axes.

Laser Conoscopy of Optically Active Crystals

The article discusses a laser conoscopic method for studying optically active crystals in order to determine such optical characteristics as the sign of rotation of the polarization plane and the optical sign of an optically active crystal from its interference conoscopic pattern obtained with circularly polarized radiation. Such a conoscopic pattern in the form of two spirals inserted into each other allows one to simultaneously and reliably determine the indicated characteristics by the orientation of the spirals and the direction of their twisting for an optically active crystal.

Noncontact Control by Laser Conoscopy of Optical Homogeneity of Heavily Doped LiNbO3: Zn

A non-contact method using laser conoscope the studies of optical homogeneity of a series of heavily doped LiNbO3crystals (4.46–4.69 mol. % ZnO). For all crystals not detected additional anomalies in сonoscopic patterns at increase of laser radiation power up to 90 mW, due to the presence of static and fluctuating defects induced in the photorefractive crystal by laser radiation.

Laser Conoscopy Study of Optical Anomalies in Uniaxial Crystals

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