Owing to the extraordinary richness of its physical properties, congruent lithium niobate has attracted multidecade-long interest both for fundamental science and applications. The combination of ferro-, pyro-, and piezoelectric properties with large electro-optic, acousto-optic, and photoelastic coefficients as well as the strong photorefractive and photovoltaic effects offers a great potential for applications in modern optics. To provide powerful optical components in high energy laser applications, tailoring of key material parameters, especially stoichiometry, is required. This paper reviews the state of the art of growing large stoichiometric LiNbO 3 (sLN) crystals, in particular, the defect engineering of pure and doped sLN with emphasis on optical damage resistant (ODR) dopants (e.g., Mg, Zn, In, Sc, Hf, Zr, Sn). The discussion is focused on crystals grown by the high temperature top seeded solution growth (HTTSSG) technique using alkali oxide fluxing agents. Based on high-temperature phase equilibria studies of the Li 2 O-Nb 2 O 5 -X 2 O ternary systems (X ¼ Na, K, Rb, Cs), the impact of alkali homologue additives on the stoichiometry of the lithium niobate phase will be analyzed, together with a summary of the ultraviolet, infrared, and far-infrared absorption spectroscopic methods developed to characterize the composition of the crystals. It will be shown that using HTTSSG from K 2 O containing flux, crystals closest to the stoichiometric composition can be grown characterized by a UV-edge position of at about 302 nm and a single narrow hydroxyl band in the IR with a linewidth of less than 3 cm À1 at 300 K. The threshold concentrations for ODR dopants depend on crystal stoichiometry and the valence of the dopants; Raman spectra, hydroxyl vibration spectra, and Z-scan measurements prove to be useful to distinguish crystals below and above the photorefractive threshold. Crystals just above the threshold are preferred for most nonlinear optical applications apart holography and have the additional advantage to minimize the absorption even in the far-infrared (THz) range. The review also provides a discussion on the progress made in the characterization of non-stoichiometry related intrinsic and extrinsic defect structures in doped LN crystals, with emphasis on ODR-ion-doped and/or closely stoichiometric systems, based on both spectroscopic measurements and theoretical modelling, including the results of first principles quantum mechanical calculations on hydroxyl defects. It will also be shown that new perspective applications, e.g., the generation of high energy THz pulses with energies on the tens-of-mJ scale, are feasible with ODR-doped sLN crystals if optimal conditions, including the contact grating technique, are applied. V C 2015 AIP Publishing LLC.

Lithium niobate is a material with many important technological applications as a result of its diverse physical properties. Using a recently derived interatomic potential, intrinsic defect energies have been calculated leading to conclusions about the defect properties of the material that are compared with experimental conclusions. The incorporation of dopant ions into the structure is also considered, and solution energies are calculated, which enable predictions to be made about which ions are most easily added and which solution energy schemes are favoured energetically.

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L 10,9 multiplet manifolds of Tb 3+ ͑4f 8 ͒ in D 2 sites in cubic garnet Tb 3 Ga 5 O 12 ͑TbGaG͒ are investigated at sample temperatures between 1.8 K and room temperature. Absorption measurements extend from 5000 to 340 nm. From analyses of temperature-dependent ͑hot-band͒ absorption spectra, many of the crystal-field split energy ͑Stark͒ levels of the 2S+1 L J multiplet manifolds of Tb 3+ are identified and confirmed from analyses of the fluorescence spectra observed between 485 and 680 nm, representing transitions from the 5 D 4 to the 7 F J manifolds. Each manifold is split by the crystal field into 2J + 1 Stark levels. Some of these manifolds, including the ground-state manifold 7 F 6 , consist of Stark levels that are accidentally degenerate, or nearly so, making transitions to or from these levels appear as unresolved spectra, even at the lowest temperature investigated ͑1.8 K͒. To resolve these spectra, we have investigated the Zeeman and magneto-optical spectra for representative manifolds 5 D 4 , 7 F 5 , and 7 F 6 at temperatures of 78 and 85 K and magnetic fields up to 7 kOe. The data are interpreted using the Stark levels and wave functions from a crystal-field splitting calculation that involved 80 individual Stark levels identified from the optical spectra of the 7 F J and quintet states reported in this study. Good agreement is obtained between the calculated and the experimental Stark levels. The calculated energy and symmetry label for each Stark level in the 5 D 4 , 7 F 5 , and 7 F 6 manifolds suitably interpret the spectral properties observed in the magneto-optical spectra, including the experimental assignment reported in the literature for the ground state as a quasidoublet ͕⌫ 1 , ⌫ 2 ͖.

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Temperature dependence of the absorption and refraction of Mg-doped congruent and stoichiometric LiNbO 3 in the THz rangeThe light induced change of refraction is studied in pure and Mg doped LiNbO 3 with congruent and stoichiometric compositions by the Z-scan method using all-lines visible argonion laser, up to MW/cm 2 intensity level. In Mg-doped congruent and stoichiometric crystals with Mg concentrations above threshold a positive change in the refractive index was found, in contrast to all other cases where beam fanning and negative change of the refractive index were observed. The beam distortion in the samples doped above threshold was related to thermal lensing, while below it to the photorefractive effects. It was also shown that for thermal lensing nonlinear absorption plays a dominant role. The Z-scan method was found to be an alternative technique to decide whether the Mg dopant level is above or below the photorefractive threshold. The damage resistance of the Mg doped samples above threshold was higher for the stoichiometric crystal than for the congruent one and increased with the amount of the built-in Mg concentration.

We report on the synthesis of a new relaxor compound with chemical formula Pb 0.78 Ba 0.22 Sc 0.5 Ta