Strontium Barium Niobate Crystal Research Articles

Luminescence of lanthanide ions in strontium barium niobate

Single crystals of strontium barium niobate, Sr x Ba 1- x Nb 2O 6, doped with the lanthanide ions Pr 3+, Nd 3+, Eu 3+, Er 3+ and Yb 3+, were grown for x in the range 0.33–0.75 using the flux growth technique. Emission and excitation spectra were recorded in the visible and near infrared range at room and low temperatures. The spectral bands are strongly affected by inhomogeneous broadening due to the intrinsic disorder of the host. The 10 K optical spectra for the Eu 3+ ion are attributed to the occupation of a single class of sites, tentatively identified as the distorted octahedral Nb 5+ sites.

Effect of external forces on the dielectric and pyroelectric properties of strontium-barium niobate crystals

It is shown that high-temperature annealing of strontium-barium niobate crystals increases the mobility of domain boundaries in these crystals. This effect manifests itself in a shift of the peak of the effective permittivity of annealed samples to weaker fields. It is ascertained that the polarization of strontium-barium niobate crystals caused by annealing results in their more homogeneous single-domain state. The effect of Ce and Cr impurities on the polarization state of the surface layers in strontium-barium niobate crystals is considered.

Synthesis of Sm 3+-doped strontium barium niobate crystals in glass by samarium atom heat processing

New glasses giving the crystallization of Sm 3+-doped Sr x Ba 1− x Nb 2O 6 (SBN) ferroelectrics have been developed in the Sm 2O 3−SrO−BaO−Nb 2O 5−B 2O 3 system, and the formation of SBN crystal dots and lines by continuous wave Nd:YAG laser (wavelength:1064 nm, power: 1 W) irradiations, i.e., samarium atom heat processing, has been examined. The formation of Sm 3+-doped SBN non-linear optical crystals is confirmed from X-ray diffraction analyses, micro-Raman scattering spectra, second harmonic generations, and photoluminescence spectra. Sm 3+-doped SBN crystal dots with the diameters of 20–70 μm and lines with the widths of 20–40 μm are written at the surface of some glasses such as 10Sm 2O 3·10SrO·10BaO·20Nb 2O 5·50B 2O 3 (mol%) by Nd:YAG laser irradiations with the irradiation times of 20–70 s for the dots and with the scanning speeds of 1–5 μm/s for the lines. The present study suggests that the samarium atom heat processing has a potential for the patterning of optical waveguides consisting of ferroelectric SBN crystals in glass substrates.

Dielectric Hysteresis Loops of Photosensitive Relaxor Ferroelectrics

We have studied the effects of illumination by a photoactive light on the polarization switching of strontium-barium niobate crystals in quasi-static periodic electric field. The illumination results in an increase of the polarization amplitude and of the most probable coercive field. The origin of this phenomenon is discussed in terms of screening of depolarizing fields and of internal random fields presenting within the bulk of a relaxor ferroelectric with photoinduced free charge carriers.

Dynamic instability of self-induced bidirectional waveguides in photorefractive media

We report on the experimental observation of a dynamic instability in the interaction of counterpropagating self-trapped beams in a photorefractive strontium barium niobate crystal. While the interaction of copropagating spatial optical solitons exhibits only transient dynamics, resulting in a final steady state, the counterpropagating geometry supports a dynamic instability mediated by intrinsic feedback. Experimental observations are compared with and found to be in qualitative agreement with numerical simulations.

Bi-layer optical waveguide formed by double boron ion implantation into strontium barium niobate crystal

We report a bi-layer optical waveguide in a Ce-doped strontium barium niobate (SBN) crystal formed by double boron ion implantation. The energies of the B + and B 3+ ions are 3 and 6 MeV, respectively, while the doses of the two boron implantation are both 2 × 10 14 ions/cm 2. A classic m-lines arrangement is performed to investigate the waveguide properties of the sample. The reconstructed refractive index profile of the waveguide shows a double-barrier confined shape, which suggests the formation of a bi-layer waveguide structure. The thickness of the two guide layers are 2.6 and 4.6 μm, respectively, which is in a good agreement with the mean projective range of the implanted boron ions of 3 and 6 MeV in the crystal. The nuclear energy loss distribution of the boron ions into SBN has a similar shape to that of the waveguide index, which means an inherent relationship between the waveguide formation and the energy deposition of the energetic ions.

Study of ferroelectric domain switching by domain wall induced light scattering

The 90°-light scattering on domain walls was probed in various strontium barium niobate (SBN) crystals for studies of the ferroelectric switching under pulsed fields. The validity of this optical method is proved by a good agreement of the switching parameters deduced from optical scattering data with those obtained with electric methods. Scanning of the scattering over the crystal bulk revealed local specialities of the switching, particularly, a marked distribution of the domain wall density D along the polar axis with a maximum close to the negative electrode. In compliance with these in situ observations, the electro-optic coefficient rc reveals a position dependence in all SBN crystals poled in the ferroelectric phase, rc decreasing from the positive to negative electrode. This regularity is interpreted in terms of the domain density distribution D(z) and accounted for by an asymmetry of the domain nucleation.

Domain switching in strontium-barium niobate crystals investigated by photorefractive self-focusing

The domain switching behaviour of undoped and Ce-doped Sr0.61Ba0.39Nb2O6 (SBN) crystals is investigated for different experimental conditions. For the investigation the photorefractive self-focusing technique is used. This method is demonstrated to be well suited for determining the polarization state of SBN crystals spatially resolved. We find that the repoling behaviour of nominally pure SBN is spatially inhomogeneous. The crystals are well repoled at the positive electrode, but are depolarized at the negative electrode. The larger the Ce doping concentration is, the smaller the depolarized crystal area. The domain switching depends on the switching velocity, while no influence of the electrode material is observed.

Electro-Optical Properties of Strontium–Barium Niobate Crystals and Their Relation to the Domain Structure of the Crystals

The electro-optical coefficients r ij and half-wave voltage V λ /2 of strontium-barium niobate crystals poled in the ferroelectric phase are shown to vary along the polar axis. The r ij ( z ) and V λ /2 ( z ) dependences indi- cate the presence of a residual domain density D ( z ) and clearly depend on the sign of the polarizing field, with r ij being minimum ( D being maximum) near the negative electrode. This character of the D ( z ) distribution and, hence, the r ij ( z ) and V λ /2 ( z ) coordinate dependences can be explained by predominant domain nucleation near the negative electrode, which is revealed when the switching processes are studied using 90 ° (Rayleigh) light scattering from domain walls. © 2005 Pleiades Publishing, Inc.

Angular and wavelength selectivity of parasitic holograms in cerium doped strontium barium niobate

The angular and wavelength selectivity of noise gratings in doped strontium barium niobate crystals for samples with two different thicknesses are investigated. We found that an offset in the optimum reconstruction angle with respect to the recording geometry occurs as a function of the thickness. This is a consequence of the unidirectional amplification. Thus the scattering intensity for the thinner sample is considerably lowered at the very recording conditions. We analyze the experimental results in terms of the kinematic theory of diffraction.

Growth and characterization of Nd-doped SBN single crystal fibers

The growth from ceramic pedestals of single crystal fibers of strontium barium niobate (SBN), doped with different Nd concentrations, was studied. High-quality fibers were grown for Nd doping levels of up to 4.2 at. %, and doping levels as high as 9.9 at. % were reached. No signs of core effects were observed, even for the highest concentration samples. The emission spectra of Nd3+ ions in the fibers did not differ from those obtained from bulk SBN crystals, showing very broad bands due to the typical disorder of the crystallographic tungsten-bronze structure. Fluorescence quenching was clearly observed for Nd doping levels above 2 at. %.

Specific features in the ferroelectric properties of Sr0.75Ba0.25Nb2O6 crystals

The dielectric properties of strontium-barium niobate crystals with a strontium concentration of 0.75, which corresponds to the most smeared ferroelectric phase transition, were measured. The dielectric hysteresis loops and the polarization relaxation are shown to exhibit clearly pronounced features characteristic of crystals with structural disorder and a broad distribution of a random internal electric field. The measurements were performed in dc, slowly varying (quasi-static), and pulsed electric fields. The experimental data obtained are used to construct the distribution function for the coercive field in the crystal bulk.

Ferroelectric switching of strontium–barium–niobate crystals in pulsed fields

In strontium–barium–niobate (SBN) polarization and switching processes under pulsed field differ from those in model ferroelectrics. In most SBN crystals, the polarization changes smoothly with relaxation times up to seconds even under fields strongly exceeding the coercive field. The kinetics are described with a power law. In some samples of a variety of compositions faster changes have been observed, but their characteristics fundamentally differ from those in model ferroelectrics. The peculiarities are evidently caused by the relaxor properties of SBN.

Optical studies of transparent ferroelectric strontium–barium niobate/silica nanocomposite

Transparent ferroelectric strontium–barium niobate (SBN) doped silica nanocomposites were prepared via a modified sol–gel process. Their structural properties were characterized by x-ray diffraction and Raman spectroscopy. It was found that by annealing the nanocomposites at temperatures between 600 and 800 °C, pure tetragonal tungsten bronze phase SBN crystallites with sizes ranging from 8 to 23 nm were obtained. Differential scanning calorimetry measurement has indicated that nanometer size ferroelectric SBN has a reduced phase transition temperature compared with that of bulk SBN. Photoluminescence and optical transmission studies of these composites have revealed noticeable blueshifts in the emission band peak and the absorption edge, respectively. The refractive index of the nanocomposite annealed at 700 °C was measured by ellipsometry. The value obtained is larger than that of pure sol–gel derived silica but smaller than that of SBN crystal, and can be described by the Bruggeman effective medium approximation.

Polarization of strontium-barium niobate crystals in pulsed fields

Polarization (ferroelectric switching) of SBN crystals in pulsed fields differs from the same process in model ferroelectrics. Polarization in most SBN crystals is characterized by slow kinetics, which can be approximated by a power-law dependence, with relaxation times of the order of seconds (in fields ). The process smoothness results in the absence of a characteristic peak in the switching-current curve. Some crystals are characterized by fast (jumplike) polarization processes, whose characteristics (the kinetics and the field dependence of the switched charge) also differ from model ones.

Simultaneous generation of coherent light in the red, green and blue from Nd3+ doped non-linear crystals

Simultaneous generation of coherent radiation at the three fundamental colours from aperiodically poled Nd 3- doped non-linear crystals is reported. In these crystals a rich variety of non-linear processes involving both pump and infrared laser radiations is possible by means of the quasiphase matching (QPM) technique. The case of Nd 3+ doped strontium barium niobate crystal (showing a random distribution of ferroelectric domains) is described in detail and its main properties are compared to those reported for other Nd 3+ doped non-linear crystals in which broadband QPM is also possible. Finally, a compilation of the latest results on simultaneous multi-frequency visible light generation obtained from Neodymium doped Strontium Barium Niobate is given.

Noncollinear optical frequency doubling in strontium barium niobate.

The observation of a novel noncollinear optical second-harmonic generation mechanism is reported. In strontium barium niobate crystals, a circular cone of second-harmonic light is generated when a fundamental beam of intensive laser light is directed along the crystallographic c axis. It can be shown that the effect is caused by the nonlinear polarization of antiparallel ordered ferroelectric microdomains.

Optical control of arrays of photorefractive screening solitons.

We discuss the creation of an array of 9 x 9 photorefractive spatial screening solitons in a strontium barium niobate crystal. We investigate the waveguide properties of each channel with a beam of different wavelength and find that the waveguides guide the probe beam independently. A supplementary beam is used to influence the paths of the array solitons and to effectively combine two channels by use of mutual attraction of solitons. To our knowledge this is the first all-optical control of an array of photorefractive solitons. Furthermore, we show that in principle image procession is possible with parallel propagation of photorefractive solitons.

Transverse modulational instability of periodic light patterns in photorefractive strontium barium niobate crystal

Interference fringes produced by the intersection of two plane waves in photorefractive strontium barium niobate crystal break in the transverse direction if the external electric field is high enough. For a certain relation between fringe spacing and nonlinearity strength, the tendency to regular pattern formation has been observed. We present a simple theory that qualitatively explains this effect.

Simultaneous generation of coherent light in the three fundamental colors by quasicylindrical ferroelectric domains in Sr0.6Ba0.4(NbO3)2

Continuous-wave red, green, and blue coherent light has been simultaneously generated by quasiphase matching in a strontium barium niobate crystal used as an intracavity frequency converter of a Nd:YVO4 laser operating at 1.34 μm. The broad distribution of ferroelectric domain sizes (1–8 μm) provides the possibility of different simultaneous frequency conversion processes without requiring angle or temperature tuning. Blue and red colors were generated by second-harmonic generation of pump (0.88 μm) and infrared (1.34 μm) laser radiation, respectively. Green light was produced by sum frequency mixing of pump and laser radiations.