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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.

The effect of Ce doping on the dielectric relaxation in Sr 0.75 Ba 0.25 Nb 2 O 6 single crystal grown by double crucible Stepanov technique has been investigated. It has been observed that the incorporation of Ce ion in the lattice reduces the dielectric maxima. It further increases the degree of diffusiveness and lowers the temperature of dielectric maxima as a result of the introduction of additional random field via created point defects. Both the undoped and Ce doped crystals undergo a non-debye type relaxation. Vogel–Fulcher fitting reveals that the attempt frequency reduced by one order of magnitude on Ce doping.

Terahertz waves are generated using a femtosecond laser pulse in a periodically poled stoichiometric lithium tantalate crystal and simultaneously detected via a non-collinear optical parametric interaction inside the same crystal. Real time up-conversion signal between the generated THz and an optic probe pulses is measured depending on the beam overlapped conditions using a general silicon-photodiode for the THz detection. The non-collinear geometry is to facilitate manipulated property of the position-dependent bandwidth at narrow and broad bandwidths of 45 GHz and 3.3 THz, respectively at the one crystal. Furthermore, an aperture effect at the detection part is characterized as the function of size and position owing to the spatial distribution of the frequency conversion signal and it is applied in optimization of the in-situ detection scheme.

We demonstrate efficient generation of a mid-IR source at 3.2 microns using a PPSLT OPO with intracavity PPSLT difference frequency mixing (DFM) crystal. This wavelength is the best suitable for ultrasonic-generation in CFRP.

c -Axis oriented single crystals of relaxor ferroelectric Sr x Ba 1− x Nb 2 O 6 ( x = 0.61 and 0.75) were investigated using polarized Raman spectroscopy and the behavior of optical phonon as a function of temperature across the phase transition from space group P 4 bm to P 4 ¯ b 2 . Based on the polarized and depolarized spectra mode assignments were carried out. Modes of symmetry A 1 (LO), B 1 , and B 2 were identified. From the detailed line shape fitting of the spectra, frequencies of the prominent modes associated with NbO 6 stretching vibration were obtained. In contrast to the earlier reported results, these modes are found to exhibit discontinuous changes across the transition. The phase transition temperatures are found to be 336 and 322 K for x = 0.61 and 0.75, respectively.

Femtosecond optical pulse is used to generate narrow-band terahertz pulses depending on a quasi-phase-matched condition in periodically poled lithium niobate (PPLN) and stoichiometric lithium tantalate (PPSLT) crystals by difference frequency generation. The origin of narrow-band THz generation proved that the two frequency components of the fs pulse contribute to the frequency mixing. By cryogenic cooling, the absorption of THz waves in the crystal is significantly reduced which results in efficient THz generation. Simultaneously generated forward and backward THz pulses were 1.38 and 0.65 THz with as narrow as the bandwidth of 32 GHz in the PPSLT sample. Temperature dependence of the generated THz waveforms had good agreement with the simulation result using one dimensional plane-wave propagation model.

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.

We investigated the effect of subgrain boundaries on periodic domain-inverted structures with a period of 30 lm in near-stoichiometric LiTaO3 (SLT) crystals and found that they negligibly affected the structures. Using SLT crystals having subgrain boundaries and a quasi-phase matching technique, we fabricated a 2-mm-thick, 60-mm-long periodically poled SLT frequency converter with a domain-inverted structure with a 30.5-lm period and demonstrated optical parametric oscillation. 2008 Elsevier B.V. All rights reserved.

The photorefractive damage (optical damage) process in Sc-doped near-stoichiometric LiNbO3 (Sc:SLN) crystals was investigated by measuring the photocurrents in these crystals for several Sc concentrations (up to approximately 1 mol%). The photovoltaic current density and photoconductivity were then estimated using the measured photocurrents. The saturated space-charge field, which is the ratio between the photovoltaic current density and photoconductivity and which causes the photorefractive damage, was then estimated. The photovoltaic current density decreased with an increasing Sc concentration while the photoconductivity increased with the concentration. This combination of decreased photovoltaic current density and increased photoconductivity means that the saturated space-charge field decreases with an increasing Sc concentration. This decrease in the saturated space-charge field apparently reduced the photorefractive damage in the Sc:SLN crystals. These behaviors are similar to those of Mg-doped LN (Mg:LN) crystals. The saturated space-charge field of the Sc:SLN crystals with no photorefractive damage was less than 100 V/cm (104 V/m), as it is for Mg:LN crystals. This means that the Sc concentration needed to obtain a less than 100-V/cm saturated space-charge field in SLN crystals is less than the corresponding value for Mg doping.

We report the acoustic imaging frequency dynamics of ferroelectric domains by low-frequency acoustic probe microscopy based on the commercial atomic force microscopy It is found that ferroelectric domain could be firstly visualized at lower frequency down to 0.5 kHz by AFM-based acoustic microscopy The frequency-dependent acoustic signal revealed a strong acoustic response in the frequency range from 7kHz to 10kHz, and reached maximum at 8.1kHz. The acoustic contrast mechanism can be ascribed to the different elastic response of ferroelectric microstructures to local elastic stress fields, which is induced by the acoustic wave transmitting in the sample when the piezoelectric transducer is vibrating and exciting acoustic wave under ac electric fields due to normal piezoelectric effects.

We study experimentally the formation of refractive index voxels (volume elements) in photorefractive LiNbO3 and LiTaO3 crystals illuminated with high irradiance femtosecond laser pulses. We used 150 fs pulses at 800 nm wavelength (energy 6–50 nJ) tightly focused inside the crystals in a single shot regime. This resulted in a formation of a micrometer size region of elevated refractive index, which may be used as memory bits in information storage/retrieval application. The maximum refractive index change of 5×10−4 was recorded in undoped LiNbO3 at an average light intensity of ∼TW/cm2 that is close to the breakdown threshold. A simple setup for photorefractive recording and in situ monitoring of the refractive index changes has been proposed.

Dielectric behaviour of Sr0.61Ba0.39Nb2O6 (61SBN) and Sr0.75Ba0.25Nb2O6 (75SBN) single crystals has been studied. It is observed that 61SBN has relatively low diffuseness as well as smaller relaxation compared to 75SBN. Increase in the configurational entropy imposed by the change in defect structure is suggested to be the origin of this behaviour. Analysis using Vogel–Fulcher expression and modified Curie–Weiss law give a signature of long-range polar order in 61SBN. The value of γ for 61SBN is closer to unity (1.14), where as for 75SBN it is 1.52. The fluctuation (in the orientation) of dipoles near dielectric maxima in SBN system is mediated by a paraelectric state.

Static and dynamic domain behavior of ferroelectric fluoride BaMgF4 single crystal was investigated using high-resolution piezoresponse force microscopy. High domain wall anisotropy was found in the as-grown BaMgF4 crystal. Antiparallel domain wall strain phenomena due to defects across the domain boundary were directly observed. The lateral domain growth in the inhomogeneous AFM tip field revealed the activation mechanism of the domain wall motion.

Two-colour holograms were recorded in a Tb-doped near-stoichiometric LiNbO3 crystal by use of extraordinary 778 nm beams for writing and an ordinary 350 nm beam for gating. The dependences of two-colour recording sensitivity and the saturated diffraction efficiency on the intensities of the recording and gating beams are presented. The saturated diffraction efficiency increased with total writing intensity, and then reached a saturated value of 56% at an intensity of 20 W cm−2. The sensitivity increased linearly with gating intensity at low intensity, and then saturated with a value of 0.08 cm J−1 at an intensity of 1.6 W cm−2. Fifty plane-wave holograms are recorded by the angle-multiplexing method and an M/# of 1.13 is obtained.

Piezoresponse mode atomic force microscopy was used to induce a dynamic polarization reversal process and to characterize domain configuration behavior in BaMgF4 single crystal. Triangular reversed domains observed on the polar and non-polar surface demonstrate a sideways domain wall motion mechanism prevailing in the switching process of the bulk BaMgF4 crystal. The domain wall bowing phenomenon due to the strong pinning of the crystal defects was first visualized in the piezoresponse image of the engineering domain pattern in BaMgF4 crystal.

Low-frequency (below 100 kHz, even down to several kHz) near-field acoustic probe microscopy for imaging ferroelectric microstructure was successfully developed based on the commercial atomic force microscope, which provides a subsurface depth profile information and as well as nanoscale spatial resolution up to 10 nm. The domain configurations of ferroelectric material were clearly visualized by this newly, non-destructive, low-frequency acoustic mode scanning probe microscopy technique with high resolution. The acoustic imaging origin is discussed in terms of interaction between the excited acoustic wave and ferroelectric domains. It is expected that the combination of the acoustic and piezoresponse mode probe microscopy in application to imaging domain structures undoubtedly enrich our understanding the nature of elasticity, piezoelectricity and ferroelectricity at submicro-, even nano-meter scale.

Difference in the terahertz generations from three types of 1 mol % MgO-doped stoichiometric LiTaO 3 crystals were analyzed. Weak single-cycle, multi-cycles, and strong single-cycle terahertz pulses were radiated at bulk, periodically poled, and angle-cut structures, respectively. The three different types of terahertz generation depend on the phase-matching process.

The isolated, six-side polygonal domain structures are observed in the orthorhombic as-grown BaMgF4 single crystal by optical microscope and atomic force microscope. The domain configurations demonstrate highly domain wall anisotropy along one principal crystal axis and polar–surface inhomogeneity. The anisotropic behaviour is due to the anisotropy of domain wall energy density in the thermodynamic equilibrium process, and the asymmetric domain surface phenomena is ascribed to the combined contribution from the local electric fields and structure defects-induced mechanical stress during the domain evolution process.

Ferroelectric domain phenomena and periodic domain patterning of orthorhombic as-grown BaMgF4 single crystal were investigated in the present study. An isolated ferroelectric domain shows a hexagonal form and exhibits a high domain-wall anisotropy. Periodic domain patterning was demonstrated on the polar surface by a periodic macropoling technique. In-plane polarization switching-induced microdomain patterning was tailored by the lateral component of the inhomogeneous electric field through a biased atomic force microscope tip. Such in-plane domain switching behavior exhibits potential promise for periodic domain engineered phonon devices.

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.

A two-dimensional mapping method was employed to investigate the homogeneity of optical parametric oscillator (OPO) performance, such as output power distribution, slope efficiency, and oscillation threshold, based on periodically poled 1 mol % Mg-doped stoichiometric LiTaO3 devices fabricated by single and multi-pulse methods. The output power decreased from the electrode-patterned face to the opposite face at low pump intensities and became homogenous over the aperture at high pump intensities. The devices fabricated by the two methods showed no large differences in OPO properties, except for better homogeneity in depth for multi-pulse devices. A large effective aperture (fluctuation < 10%) of 1.4×1.3 mm2 was obtained in both types of devices.

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.

Pure and Mn doped single domain near stoichiometric lithium niobate crystals have been grown by top seeded solution growth from 55 mol% Li solution. A uniform segregation of Mn throughout the crystal was obtained. Doping concentration decreases the Curie temperature while the absorption edge shift towards the longer wavelength region. Two color holographic recording was examined in Mn doped samples. Improved sensitivity, dynamic range and lifetime of the hologram for the doped crystal have been determined. The effect of Mn doping on the switching properties has been analyzed.

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.

Pure and MgO doped (up to 4 mol%) near-stoichiometric LiNbO 3 crystals are grown from Li rich (Li-55 mol%) melt. Significant improvement in the optical properties such as increase of optical damage resistance, accompanied by a shift in the –OH peak position in FTIR spectrum, and transparent range is observed at 1.75 mol% of MgO concentration in the crystal. Also the coercive field required for ferroelectric domain switching is minimum at 1.75 mol% MgO doping. Based on the results, the correlation between the defect structure and ferroelectric domain switching behavior in pure and MgO doped SLN is discussed.

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.

For pure SLN and SLT crystals the coercive field measured from ferroelectric hysteresis loop was found to be independent of ramp rate. Decreased lithium concentration in pure SLN samples, the coercive field and internal field are strongly enhanced. Nb Li antisites are the major contribution to the internal field. Coercive field depends strongly on the ramp rate in case of MgSLN and MgSLT samples, because of domain pinning. The coercive field is considerably reduced in Mg doped SLN and SLT compared to pure samples, indicating that the switching fields are strongly dependent on the nonstoichiometry of the crystals. The coercive field values were found to be constant under multiple cycling in case of Mg (1 mol%) doped SLN crystal. A strong correlation is found to exist between coercive field value and the Curie temperature.

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.

The growth characteristics and properties of large size SrAlF5 single crystals are described and compared with those of BaMgF4. SrAlF5 shows a higher grade of transparency and a larger nonlinear effective coefficient as well as uniaxial and ferroelectric nature, on contrast to the one order smaller nonlinear coefficient and biaxial character of BaMgF4. The Sellmeier and Cauchy coefficients are obtained fitting the measured ordinary and extraordinary refractive indices, and the grating period for the first order quasi-phase matching (QPM) is estimated as a function of the wavelength. The higher potential of SrAlF5 in comparison with BaMgF4 for the realization of all-solid-state lasers in the ultraviolet wavelength region by the QPM technique is pointed out.

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.

Near-stoichiometric LiNbO3 crystals slightly doped with Mn from melts with different compositions are grown by the top seeded solution growth method. The growth parameters such as temperature field, pulling, and rotation rates are optimized. Two-color holograms are recorded in these crystals by the use of a near infrared laser of 778 nm for writing and an ultraviolet laser of 350 nm for gating. The light-induced absorption changes and two-color holographic characteristic performances are presented and compared. The results show that crystals with composition closer to stoichiometry exhibit better two-color holographic storage performance.

The two-color photorefractive properties in undoped as-grown near-stoichiometric lithium tantalate crystals were investigated, where a near-infrared laser and a cw ultraviolet beam were used for writing and gating, respectively. The key parameters in characterizing two-color photorefractive effect, light-induced absorption change, two-color sensitivity, refractive index change, readout characteristics, and dark decay were measured by changing intensities of gating and writing beams, wavelengths of gating and writing beams for the crystals with different near-stoichiometric crystal compositions, and proton concentrations. The results showed that there exists an optimal crystal composition of around 49.65% for both sensitivity and refractive index change together with moderate lifetime of small polarons. The achieved refractive index change was on the order of 10−4, and the obtained maximum sensitivity was 0.18 cm/J. The extrapolated lifetime of holograms at room temperature in the crystals without observab...

We show that doping of near stoichiometric lithium tantalate with magnesium leads to enhanced interband photorefractive effects compared with undoped crystals. Investigations are performed at the deep ultraviolet (UV) wavelength λ UV =257 nm by Bragg diffraction experiments. The formation of two grating components with a destructive mutual phase shift is observed. For UV light intensities larger than about 500 mW/cm 2 the typical time constant for the response of the interband grating is faster than one millisecond. We also observed quasi-fixing of holographic gratings with UV light and nondestructive, optically switchable readout at the wavelength λ HeNe =632.8 nm.

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.

The magnetooptical properties and magnetic-field-sensing properties of bulk Ce-substituted YIG (Ce x Y 3− x Fe 5 O 12 ) crystals were studied. There was an absorption edge at 1200 nm and a large negative Faraday rotation was obtained. Faraday rotation was increased to a greater extent by Ce substitution than by Bi substitution. The magnetic-field sensitivity of Ce 0.24 Y 2.76 Fe 5 O 12 was 0.0048% m/A which was larger than that of (BiGdLaY) 3 (FeGa) 5 O 12 . The optical current transformer (CT), using a Ce:YIG crystal as a sensor head, could measure the alternating steady state, faulting, breaking and reclosing currents. These results suggest that cerium-substituted yttrium iron garnet is a high-performance material suitable for magnetic-field (or electric-current) sensors.

The atomic structure of LiNbO 3 (0 0 0 1) surface was investigated by low-energy neutral scattering spectroscopy (LENS). Poled stoichiometric LiNbO 3 (SLN) samples were prepared for the measurements. The LENS was developed for surface structure and composition analysis particularly of highly insulating materials and was successfully applied to the structure analysis of the SLN(0 0 0 1) surface. The polar angle dependences of intensity of scattered He 0 from the poled SLN surfaces indicate obvious differences between the negatively and the positively charged surfaces. It is suggested that O atoms cover the surfaces, and the first metal layers underneath the O layer consist of Li and Nb for negatively and positively charged surfaces, respectively, parallel to the applied electric field.

We investigate two-color holography using Tb doped near-stoichiometric LiNbO 3 . We present the measurements of the hologram strength and sensitivity dependences on the wavelength and intensity of the writing near-IR laser light and on the gating UV light intensity. The diffraction efficiency of the holograms is satisfactory when the writing light wavelength is below 800 nm. The rapidly changing sensitivity around the photon energy of 1.6 eV is an indication that small polarons are involved in the recording mechanism. The recording speed mainly depends on the gating beam intensity, while the hologram strength is much more affected by the writing beam properties, both the intensity and wavelength. We show how to choose appropriate intensities to optimize the desired two-color performance that can be also applied to other two-color schemes.

We investigated the photoluminescence properties of near-stoichiometric LiNbO3 crystals doped with Tb only and double doped with Tb and Fe. Excitation spectra for the emission from the 5D4 state in both crystals have been studied in the range 200-500 nm. We observed two broad ultraviolet absorption bands and discussed their relations to Tb ions. Temperature dependence of the 5D4 emission intensity and lifetime showed strong quenching below room temperature.

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.

We have investigated nanoscale ferroelectric-domain engineering of a Sr 0.61 Ba 0.39 Nb 2 O 6 (SBN) single crystal using a scanning force microscope (SFM). A high-quality single crystal of SBN was grown by a newly developed double-crucible Stepanov method. The SBN crystal fixed on metal substrate was polished to a thickness of approximately 55 μm. Artificial nanoscale patterns of domain structures such as inverted-domain dot and inverted-domain mesh patterns were fabricated in the SBN samples, in which polarization directions of the domains were locally switched by scanning a SFM conductive cantilever along the sample surfaces under applied voltages. These results demonstrate that nanoscale domain patterning of ferroelectric single crystals, such as the SBN crystal, by using SFM is promising for creating novel functional devices.

The wavelength dependence of the space-charge field as induced in near-stoichiometric LiTaO3 crystals is investigated by measuring the bulk photogalvanic effect and the photoconductivity. LiTaO3 crystals of composition nearer to stoichiometry exhibit a pronounced reduction of the saturated space-charge field, which results from a larger increase in the photoconductivity relative to the photogalvanic effect. Especially, at near-UV wavelengths, the saturated space-charge field of the order of 0.1 kV/cm reaches a minimum that is two orders of magnitude lower than typical values observed in undoped near-stoichiometric LiNbO3.

Photorefractive damage at u =532 nm and green-light-induced infrared absorption (GRIIRA) of near-stoichiometric LiTaO 3 (SLT) single crystals were investigated. The SLT crystal even without MgO doping showed high photorefractive damage resistance and suppressed GRIIRA. In addition, a small amount of MgO doped into the SLT crystal almost eliminated the photorefractive damage and GRIIRA. A 3-mm-thick periodically poled SLT (PPSLT) and a 1-mm-thick periodically poled MgO-doped SLT (PPMgSLT) were successfully fabricated and their optical parametric oscillation (OPO) performances were investigated.

We demonstrate 43% slope efficiency for generation of ~3200 nm light, a wavelength considered to be ideal for laser induced ultrasound generation in carbon fiber reinforced plastic. High slope efficiency was obtained by optimizing crystal lengths, cavity length and mirror reflectivity using a two crystal optical parametric oscillator+difference frequency mixing (OPO+DFM) nonlinear wavelength conversion scheme. Mid-IR output >12 mJ was obtained from a 1064 nm Nd:YAG pump laser with 12 ns pulse width (FWHM) and containing pulse energy of 43 mJ. A compact, single temperature crystal oven is described along with some suggestions for improving the slope efficiency.

More than 300mW of 355nm generation was confirmed by cascaded configuration from 1064nm pulsed laser by using PP-LBGO (LaBGeO5) without walk-off. Measured temperature tolerances are 8.4 K-cm, which is almost double of Type-II LBO.

We have observed that newly developed near-stoichiometric LiNbO 3 crystals doubly doped with Tb and Fe have three different types of energy levels: ultraviolet (UV) absorption centers just above the valence band, metastable shallow electron traps slightly below the conduction band, and deep traps located about 1.9 eV below the conduction band. Irradiation with UV light induced a stable absorption band extending from λ 650 nm to the absorption edge, which is caused by the photoinduced charge transfer from UV-sensitive absorption centers to deep traps (Fe 3+ ) via the conduction band. The electron lifetimes at shallow and deep traps could be controlled by doping concentrations. Based on these favorable energy states, nonvolatile two-color holographic recording has been demonstrated by use of 852 nm recording beams and UV gating light. Quasi-nonvolatile one-color recording at 532 nm has also been demonstrated in these codoped crystals. Hologram recording from the UV-exposed, colored state revealed a much improved sensitivity in comparison to that from the uncolored state. The obtained M/# was 1.73 for a 3.3 mm-thick crystal.