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We focused on LaBGeO5 (LBGO) single crystal as a novel ferroelectric material for quasi-phase-matching (QPM) devices which are suitable for UV generation. In order to enhance the conversion efficiency of periodically poled LBGO (PP-LBGO), it is required to grow large diameter crystal to obtain PP-LBGO device with long interaction length. However, poly-crystallization were easily happened during LBGO single crystal growth process, and there were several difficulties to increase the diameter. In order to investigate the cause of poly-crystallization, a part of polycrystalline LBGO was characterized by powder X-ray diffractometer. As a result of the measurement, the polycrystalline parts slightly contained La2Ge2O7 phase. By considering the evaporation of B from the melt and optimizing growth conditions, LBGO single crystals with a diameter greater than 30 mm were successfully grown.

We grew Sc-doped near-stoichiometric LiTaO 3 (Sc:SLT) crystals from Li-rich (61 mol% Li) solutions with Sc concentrations of up to 1.0 mol% by using a top-seeded solution-growth method. We investigated the effect of the Sc-doping on the effective distribution coefficient, the optical damage (photorefractive damage), the OH − absorption peak position, the Curie temperature, the transmittance spectra, the UV absorption edge, the electric field for domain inversion, the ordinary and extraordinary refractive indices, and the thermal conductivity along the Z -axis. Crystals doped to an Sc concentration of at least 0.44 mol% showed no optical damage at a wavelength of 532 nm. This concentration is low compared to the 1.0 mol% Mg-doping concentration required to suppress optical damage in SLT crystals. The thermal conductivity of these Sc(0.44 mol%):SLT crystals was closer to that of pure SLT crystal than was that of Mg(1.0 mol%):SLT crystals. This means that Sc:SLT crystal is a promising candidate material for use in high-power lasers used for quasi-phase-matching frequency conversion.

Pure and MgO (0.5. 0.7 and 1 mol%)-doped near-stoichiometric lithium tantalate (near-SLT) crystals of 4-in diameter have been grown from off-stoichiometric melt using a double crucible. The grown crystals are free from cracks and twins. The addition of MgO increases the Curie temperature. SLT crystals with 0.7 mol% or more MgO doping concentrations showed enhanced optical damage resistance. The ordinary ray refractive indices in MgO-doped SLT crystals are slightly lower than the corresponding index of non-doped crystal. On the other hand, the extraordinary ray index of SLT is unaffected upon MgO doping. Periodically poled structures of 8 μm period have been fabricated over a length of 40 mm for 532 nm green generation through quasi phase matching.

Nd, Mg co-doped near-stoichiometric LiNbO 3 (Nd:Mg:SLN) crystals were grown from Li-rich solutions by a top-seeded solution-growth (TSSG) method. Doping of Mg 1 mol% was used to suppress photorefractive damage and the Nd nominal concentration added to the solution was either 0.1, 0.2, 0.5, 0.9, or 1.8 mol%. From the analyzed Nd concentration in the Nd:Mg:SLN crystals and nominal Nd concentration in the solutions, the effective distribution coefficient k eff for Nd was calculated to be 0.12. The thermal conductivity of these crystals was found to be sensitive to non-stoichiometric defects (Nb anti-site defects)—the thermal conductivity of the Nd:Mg:SLN crystal was found to be about 1.3 times as large as that of the Nd, Mg co-doped congruent LiNbO 3 (Nd:Mg:CLN) crystal. From the viewpoint of laser materials, this increased thermal conductivity is advantageous even if other laser properties are almost the same. The optical absorption and emission spectra of Nd:Mg:SLN crystals were found to be almost the same as those of the Nd:Mg:CLN crystal.

Ti-diffused planer waveguides have been fabricated on pure and Mg-doped near stoichiometric lithium niobate (SLN). Secondary ion mass spectroscopy method was applied to study the Ti diffusion in 1 mol% Mg-doped Z-cut SLN crystal. 100 nm Ti film has been deposited on LN substrate by e-beam evaporation at room temperature. Diffusion constant value for Mg-doped SLN is lower (1.84×10 −13 cm −2 /s) than that of pure SLN. Mg-doped CLN also possesses low diffusion constant value of 1.27×10 −13 cm −2 /s due to higher doping concentration of Mg (5 mol%). AFM topographic observation reveals that Mg-doped SLN shows lower surface roughness than Mg-doped CLN. The roughness (peak to valley) of the Ti-diffused Mg:SLN is 20 nm compared to 62 nm for the congruent LN waveguide. These features make Mg:SLN highly attractive for the fabrication of efficient waveguides.

We present the aspects on the growth of 4-in diameter near-stoichiometric lithium tantalate (SLT) crystals, from lithium-enriched melt, employing double crucible Czochralski (DCCZ) technique. The difficulties encountered during growth such as crack and mechanical twin formation are discussed in detail and the same overcame by adopting suitable experimental parameters. The wafers sliced from the crystals are found to be compositionally homogeneous and free from sub-grains. The variation in the refractive indices across the wafer is of the order of 10 −5 . We could not observe any marked difference either in the absorption edge or poling field for domain inversion at different locations in the wafer.

Sc-doped near-stoichiometric LiNbO 3 (Sc:SLN) crystals were grown from Li-rich solutions with Sc concentrations of up to 1.3 mol% by a top-seeded solution-growth method. We investigated the Sc-doping effects on the effective distribution coefficient, photorefractive damage (optical damage), the OH-absorption peak position, transmittance spectra, the ordinary and extraordinary refractive indices ( n o and n e ), and the electric field needed for domain inversion. The Sc:SLN crystals doped with a Sc-doping concentration of 0.4 mol% or more showed no photorefractive damage. This critical Sc-doping concentration in the SLN crystal was one-fifth that in a congruent-melt composition LN (CLN) crystal which requires at least 2 mol% Sc (1 mol% Sc 2 O 3 ) to suppress photorefractive damage. The 0.4 mol% Sc doping needed to suppress photorefractive damage in the SLN crystal was also low compared to the 1 mol% required for Mg doping. Except for n o and n e , all of the measured properties were influenced by the Sc-doping effect.

SrAlF 5 has recently become one of the most promising candidates for the realization of all-solid-state lasers in the ultraviolet wavelength region by the quasi-phase-matching technique. It has been shown that it is highly transparent down to the cutoff wavelength at about 150 nm, optically uniaxial and ferroelectric. The refractive index of SrAlF 5 from the ultraviolet to the near-infrared wavelength region is measured by the minimum deviation method. The Sellmeier and Cauchy coefficients are obtained from the fits to the curves of the ordinary and extraordinary refractive indices, and the grating period for the first-order quasi-phase-matching is estimated as a function of the wavelength. The effective nonlinear coefficient is similar to that of quartz, d eff ≈ 0.3 –0.4 pm/V, and the poling periodicity for 193 nm SHG from 386 nm is 4.1 μ m .

Bismuth silicon oxide (Bi 12 SiO 20 ) single crystals were grown from the melts with different SiO 2 mole percentages and with different dopants by Czhochralski technique. The absorption coefficient for these crystals depends on the stoichiometry of the melt composition. Photoluminescence emission spectra for the grown crystals were measured from 80 to 293 K. The spectra present a broad structureless peak at 80 K. The interband transitions for different stoichiometric crystals were analysed and the behavior seems to be independent of composition unlike the bismuth germanate crystals. The three level interband model proposed for the BGO crystals completely explains the interband transitions in BSO crystals also.

In this paper we consider the problem of thermal stress inhibition in double crucible Czochralski crystal growth by means of a thermal tube with linear temperature distribution computationally determined from solution with adiabatic boundary condition, which provides the formation of a stressless one-dimensional temperature distribution along the growing crystal. We study how this linear temperature distribution applied along the thermal tube is “transferred” into the growing crystal depending on the gap between crystal and inner tube surfaces, within which complex radiative–convective heat transfer takes place. Calculations presented in the paper suggest that linear temperature distribution along the thermal tube allows an order of magnitude stress reduction in 80–100 mm diameter crystals of LiNbO 3

Thermal analysis of the initial stage of crystal growth from melt reveals the specific temperature distributions which lead to the onset of compressive stress inside the crystal shoulder formed from the initial seed. This compressive stress increases with increase in the shoulder angle. The specific temperature distribution is also characterized by the significantly decreased temperature gradient at the growth interface which may lead to morphological destabilization. The initial stage of growth, i.e. crystal diameter increase from the seed, should be performed at significantly lower pulling rates as compared with the pulling rates applied to the constant diameter crystal.

Titanium-doped near-stoichiometric LiNbO3 (SLN) crystals were grown from lithium-rich solutions with a Ti concentration of up to approximately 20 mol% by a top-seeded solution-growth (TSSG) method. Ti-doped SLN (Ti:SLN) crystals with a Ti concentration of up to 9 mol% were free from inclusions, voids, cracks, or mechanical twins. The effective distribution coefficient keff for Ti in the Ti:SLN crystals was found to be approximately 0.45±0.05 for the Nb atom in the above composition range. The Ti-doping effects on Curie temperature, UV absorption edge, changes in the ordinary and extraordinary refractive indexes (Δno and Δne), and lattice constants were investigated. The Curie temperature for the Ti:SLN crystals linearly decreased with increasing Ti concentration up to 9 mol%. Both Δno and Δne linearly increased with increasing Ti concentration up to 9 mol%, and Δne was much larger than Δno over the entire wavelength range from 440 to 1550 nm. The UV absorption edge for the Ti:SLN crystals shifted to longer wavelengths with increasing Ti concentration. The a- and c-axes lattice constants in the Ti:SLN crystals decreased with increasing Ti concentration. In addition, a photoelastic effect on the refractive-index changes in the Ti:SLN crystal was estimated from the lattice-constant data.

Optical-quality near-stoichiometric lithium tantalate (SLT) crystals doped with Nb were grown by top seeded solution growth technique using induction-heating system. The crystalline wafers were subjected to optical transmittance studies and coercive field measurements. The optical transmittance spectra of doped crystals show a shift in the absorption edge towards longer wavelength side. A change in Curie temperatures with respect to doping concentrations of Nb has been observed. Hysteresis measurements reveal that the coercive field value increases for increasing niobium concentration. It has also been observed that there is a significant increase in the internal field value for Nb-doped SLT crystals.

Single crystals of strontium barium niobate (SBN) solid solution, (Sr x Ba 1− x ) 1− y (Nb 2 O 5 ) y , 0.75⩾ x ⩾0.40, 0.5050⩾ y ⩾0.4975, were grown by the floating zone method. There are two series of the crystals. x varies and y is fixed at 0.5 in the first series of crystals. x is fixed at 0.61 and y varies in the second series. The typical size of the grown crystal is 5 mm in diameter and 70 mm in length. All crystals, regardless of the compositions, revealed the facet parallel to the c -plane and the clear striations. A part around the crystal can be easily broken due to hoop stress. The spontaneous growth-direction of SBN is 〈0 0 1〉. The congruent melting composition of SBN is revealed by employing a zone-melting method at the final stage of growth experiments. It is (Sr 0.61 Ba 0.39 ) 0.5015 (Nb 2 O 5 ) 0.4985 . The absorption edges of the crystals in both series are around 360 nm and are shifted by 10 nm toward blue in comparison with those of the crystals grown by CZ method.

Lithium tantalate (LiTaO 3 ) single crystals having different Li/Ta ratios were grown by using conventional and double crucible Czochralski method. The grown crystals appeared to have mole percent of Li 2 O ranging from 45.5 to 50 mol%. We analyzed the real composition with ICP method and measured the Curie temperatures (T c ) with DTA method. The relationship between T c and the mole percent of Li 2 O in LiTaO 3 crystals was derived. The transmission spectra and refractive indices were measured. The refractive indices measured by prism coupler were analyzed in terms of single-term Sellmeir parameters.

Strontium barium niobate (SBN, (Sr 0.61 Ba 0.39 ) 0.5015 (Nb 2 O 5 ) 0.4985 ) was grown by using Stepanov technique (ST) or double crucible Stepanov technique (DCST). DCST is a modified Stepanov technique in which the inner crucible is introduced to reduce the temperature fluctuation inside the die. The change of refractive indices was estimated from the interference fringe of the grown crystal. In addition, the change in Sr concentration was estimated by using the relationship between the composition and the extraordinary refractive index. The local variation in the refractive index of the crystal grown by DCST is less than or equal to 3×10 −5 and is 1/3 of the value of the crystal grown by ST. The corresponding fluctuation in Sr concentration for the crystal grown by DCST is 0.0003, which is 1/3 of the value of the crystal grown by ST.

Codoped lithium niobate of congruent and stoichiometric compositions had been successfully grown specifically for holographic data storage applications. The dopants we have selected are Mn and Ce and their role in the recording process is described. Growth methods, sample preparation, doping level measurements, holographic recording data as well as the results of optical characterization and photorefractive properties of the two-photon sensitivity are discussed. Compared to the previously grown crystals, the codoped LiNbO 3 shows a higher sensitivity and dynamic range for recording in red ( λ=632 nm ).

Undoped and MgO-doped LiNbO 3 single crystals with near-stoichiometric compositions were grown from K 2 O-doped melts and Li-rich melts by two different growth techniques. Near-stoichiometric LiNbO 3 single crystals, having large [Li]/[Nb] ratios of 0.988–0.993, showed smaller threshold concentrations of MgO than congruent crystals for the behavior of Curie temperature, OH absorption band and optical damage properties. We discuss the ideal defect structure models, and find that the Li-site vacancy model is consistent with the experimental results for MgO-doped near-stoichiometric LiNbO 3 single crystals.

Nondoped and MgO-doped LiNbO 3 single crystals of 30 mm in diameter and 25–30 mm in length were grown by the top-seeded solution growth method. The solution with [Li]/[Nb] ratio of 1 contained K 2 O component of 10.6 mol% (7 wt%). MgO of different concentrations was used to dope the solution. As-grown crystals were transparent, void-free and almost free from potassium contamination. The crystal grown without MgO-doping exhibited a Curie temperature of 1193°C, indicating that the crystal composition was considerably close to stoichiometry. The MgO-doped crystals grown from the above solution showed larger [Li]/[Nb] ratios (that is, closer to stoichiometry) than the crystals grown from the congruent composition melt doped with MgO of the same doping levels. The MgO-doped crystals with near stoichiometric composition showed a shift in absorption edge towards shorter wavelength, an increase in Curie temperature, and four orders of magnitude increase in photorefractive damage resistance compared to nondoped crystals grown from the congruent melt by the conventional Czochralski method.

With the aim of finding an optimum crucible for growth of Pr2−xCexCuO4 crystal, reactions between CuO flux and various crucible materials were studied. Among six different crucible materials, Pt, Al2O3, ZrO2, Y2O3, CeO2 and MgO, Pt crucible was suitable for using Ce free solution. For Ce doped solution, MgO crucible was better than other materials. The reactant between Pt crucible and CuO flux was identified as Pt2Cu. In the case of MgO crucible, Mg2CuOx and (Mg,Cu)Ox were produced as reactants. We found a method to restrain the reaction between the crucible and the solution. Using this method for growth of Ce doped crystal, we grew a crystal of size 30 mm∅×1.5 mm.

Optical quality near stoichiometric lithium niobate (SLN) and Mn-doped SLN crystals have been grown by top-seeded solution growth from 55 mol% Li-rich solution. A uniform segregation of Mn throughout the crystal was obtained. Doping of Mn decreases the Curie temperature while the absorption edge shifts towards the longer wavelength region. The effect of Mn doping on the switching properties has been analyzed.

Single crystals of LuFe2O4, LuFeCoO4 and YbFeMgO4 (YbFe2O4 structure with space group R3m) were grown by the floating zone method. The atmosphere of CO2-CO gas mixture was used for growth of LuFe2O4 crystal, and the flowing air for growing both LuFeCoO4 and YbFeMgO4 crystals. The growth rate was 1 mm/h, and the growth direction was perpendicular to the c-axis in the hexagonal system for all cases. Single crystals attaining 3x2x15 mm, 1x5x10 mm and 5x3x20 mm were obtained for LuFe2O4, LuFeCoO4 and YbFeMgO4, respectively.

A single crystal of Bi 2.0 ( Bi 0.2 Sr 1.8 Ca 1.0 ) Cu 2.0 O 8 was grown by the floating zone method. This compound melts incongruently and the grown boule is an aggregate of large single crystal grains with growth direction perpendicular to [001]. The crystals tend to grow along the direction [100] and can be easily cleaved along the (001) plane. The grown crystal has orthorhombic symmetry with superstructure and the cell constants a , b and c of the sub-cell are 5.43, 5.43 and 30.63 A, respectively. This crystal reaches zero resistance state at 92 K.