Barium Sodium Niobate Crystals Research Articles

Raman and Hyper Raman opalescence on the soft mode in barium sodium niobate crystals

Abstract A strong increase in the spectral intensity of Raman scattering (Raman opalescence effect) at the polar soft mode, responsible for the instability of the crystalline lattice, near ferroelectric phase transition points in the barium sodium niobate (BSN) crystal was found. Raman opalescence is explained as a consequence of a sharp increase in the amplitude of the transverse A1(Z; TO) polar optical soft mode near the temperature of the ferroelectric phase transition in BSN (Tc = 830 K). Experimental results were obtained using a new experimental technique, based on the construction of isofrequency temperature dependences, when registering the spectral intensity of Raman scattering at fixed frequencies of the spectrometer, near the frequency of the exciting line, for certain polarization geometry. The conditions for observing the effects of Hyper Raman opalescence near the phase transition temperature in the BSN are established.

Nanodomain structures in nonlinear crystal

Thermal properties of barium sodium niobate crystals were investigated by means of light scattering methods in the temperature range of 20–600°С. Three types of pictures, ellipses, rounds, stripes, have been observed on the screen in the far field depending on the temperature and polarization of the laser beam relatively to the crystallographic axes. The changes of the type of scattering are correlated with structural phase transitions at about 300 °C and 560 °C and with the evolution of the nano-domain structures at about 200 °C and 250 °C. Image analysis in the temperature region of 20–600 °C and comparison with the structural investigations below 300 °C allow to made conclusion that incommensurate phase in the temperature range of about 500–550 °C has the quasi-tetragonal symmetry.

Change in the refractive index of a photorefractive crystal during formation of a spatially screened soliton

A change in the refractive index of a photorefractive barium-sodium niobate crystal in an alternating electric field during the propagation of intensity-modulated coherent radiation in it is studied. It is shown experimentally that a change in the refractive index in the soliton regime in a photorefractive crystal with a small nonlocal response is independent of the external-field amplitude and intensity-modulation depth.

Role of the local response of a photorefractive medium in the formation of a spatial screened soliton

The propagation of intensity-modulated laser radiation in a barium—sodium niobate crystal is studied in an external electric field. The possibility of controlling a nonlinear local response of the crystal is demonstrated. It is shown experimentally that the conditions of formation of a one-dimensional spatial soliton can be changed by varying the nonlinear response of the crystal.

非线性铌酸钡钠晶体中纳米范围结构的热变化研究

By the 90 deg. elastic light scattering investigation and far field observation in the range of 20-800 centigrade, the relation between behavior of light scattering anomalies and evolution of nanodomain structures in lattice of barium sodium niobate (Ba_2NaNb_5O_15, BSN) crystal was clarified. The correlation between anomalies on the temperature curves of the elastic light scattering intensity and temperature transformations of nanodomains was studied by X-ray and electron microscope methods. Phase transition near 500 centigrade and movement in field of scattering light could be explained by appearance of a new incommensurate phase.

INVESTIGATION OF PECULIARITIES OF LIGHT SCATTERING BY NANOSTRUCTURAL CHANGES IN THE CRYSTAL LATTICE OF FERROELECTRIC BARIUM SODIUM NIOBATE CRYSTAL

Thermal changes of light scattering images in the far-field were observed under steady illumination by an incident laser beam of finite beam width on barium sodium niobate crystals in the temperature range of 20–500°C. Different patterns of light scattering in far-field were observed — from striped to round-like form with dependence on temperature, conditions of grown, direction of beam and polarization. The round-like form was observed on cooling from 450°C to 240°C. Striped forms of light scattering were observed below 200°C. Correlation of the behavior of elastic light scattering was observed in this temperature range.

The decay of low-frequency elastic oscillations in a Ba2NaNb5O15 crystal

The internal friction and shear modulus of a barium sodium niobate crystal were studied using the torsion pendulum technique at a frequency of ∼25 Hz in the temperature range from 80 to 800 K. An internal friction relaxation peak of the domain nature was observed at 228 K. A relaxation process responsible for this internal friction peak is explained through compensation of the electric charge (induced by a piezoelectric effect at the 180° domain walls) by charged point defects diffusing toward the domain walls.

Raman and Infrared Spectra of Nd-Doped Barium Sodium Niobate Crystals

Neodymium-modified barium sodium niobate (Ba2Na)1-xNdxNb5O15(BNN:Nd), with x = 0.025, crystallizes with a filled tungsten bronze (TB) type structure in the tetragonal system, conforming to the space group P4bm and Z = 2. The lattice constants are a = 1.2446(1) and c = 0.3991(1) nm at room temperature. Tc = 537 +- 2 °C. The experiments show that the Nd-ions effectively improve crystal structural quality. The lattice vibrational spectrum, studied by Raman and infrared reflectivity spectroscopy, shows that the crystal microscopic structure and lattice dynamics, thereby the microstrain and microstress, are very stable in a temperature range from 22 to approaching 500 °C.

Raman and Infrared Spectra of Nd-Doped Barium Sodium Niobate Crystals

Raman and Infrared Spectra of Nd-Doped Barium Sodium Niobate Crystals

Energy state of Nd3+ doped in barium sodium niobate crystals

Nd-doped barium sodium niobate (Ba2Na)1−xNdxNb5O15 (BNN:Nd), with x=0.025 and a Curie temperature of 537±2 °C, crystallizes with a filled tungsten bronze-type structure in the tetragonal system. The lattice constants are a=b=1.2446(1) and c=0.3991(1) nm at room temperature. There are two formulas per unit cell. The five typical deep energy levels, formed by the Nd3+ ions doped in the A1 and A2 sites, are 2.36, 2.12, 1.68, 1.55, and 1.43 eV. Investigating the green and yellow second-harmonic generation shows that the BNN:Nd crystal can be expected as a useful material for the green, especially for the yellow laser radiation at room temperature.

Spatial self-phase-modulation of light in a photorefractive crystal subjected to an external alternating field

A mechanism of spatial self-phase-modulation of light in a photorefractive crystal subjected to an external alternating electric field is proposed. An experimental study of such modulation is reported for a barium sodium niobate crystal.

High-frequency resonance in acoustic superlattice of barium sodium niobate crystals

By using growth striation technique, an acoustic superlattice of barium sodium niobate crystals, the single crystals with the periodic laminar ferroelectric domain structures, has been prepared. High-frequency resonance in the range of 200–400 MHz in such materials has been realized experimentally. The experimental results indicate that the application of acoustic devices with low acoustic loss operating at high frequencies is expected.

Thermally induced optical damage to barium–sodium niobate crystals

Thermally induced optical damage (TIOD) was observed in undoped barium–sodium niobate (BSN) crystals as a result of changes in their temperature. This damage was deduced from the behavior of YAG:Nd3+ laser radiation when a BSN crystal was inserted in the resonator and also using a helium–neon laser probe beam. The experimental results were satisfactorily explained by the familiar pyroelectric model of TIOD and, in the crystals studied, an inhomogeneity of the conductivity rather than an inhomogeneity of the pyroelectric constant played the main role.

Domain structures induced by defects in Ba2NaNb5O15and LiNbO3

Abstract Systematic observations of ferroelectric and ferroelastic domains induced by defects, such as dislocations, inclusions and twins, are reported for as-grown barium sodium niobate and lithium niobate crystals. The main characteristics of defect-induced domains in these crystals are described. It is found that shapes of ferroelectric domains induced by dislocations depend upon directions of dislocation lines and domain structures of matrix in both crystals, and are related with the Burgers vectors in LiNbO3 but are independent of them in Ba2NaNb5O15.

Loop oscillator with a holographic amplifier

A report is given of the first loop oscillator utilizing a photorefractive barium sodium niobate crystal and a holographic amplifier with a similar crystal inside the loop. It is shown that the amplifier reduces the threshold value of the coupling constant and increases the reflection coefficient of a phase-conjugate wave (the maximum value found in these experiments was ~ 50%). The conditions for optical bistability in this loop are considered.

Photorefractive barium sodium niobate

Abstract Recording of transmission and reflection dynamic holograms, beam coupling, phase conjugation due to backward-wave four-wave mixing, and coherent optical oscillation with frequency degenerate pump have been studied in nominally pure barium sodium niobate crystals.

Small-signal amplification in the electrical conductivity of barium sodium niobate crystals.

We observe a resonance behavior of oscillations prior to Hopf bifurcations in an autonomous system. The system studied is a barium sodium niobate crystal in which voltage oscillations are induced by a periodically modulated current density. The resonance behavior is measured as a function of the dc-offset current density. The shape of the resonance peak and its dependence on the dc offset are found to be in fair quantitative agreement with recent theoretical studies.

Circle maps and mode locking in the driven electrical conductivity of barium sodium niobate crystals.

Instabilities in the electrical conductivity of barium sodium niobate crystals are studied with ac and dc fields. Phase portraits, Poincar\'e sections, and return maps are constructed from measured signals in the quasiperiodic state. We show that the dynamical behavior of the system can be modeled by a 1D circle map. Mode locking is observed in the system prior to the transition to chaos; the mode-locked intervals exhibit a devil's staircase behavior.

Oscillatory and Chaotic States of the Electrical Conduction in Barium Sodium Niobate Crystals

Evidence is presented for oscillatory and chaotic behavior of the electrical conduction measured in barium sodium niobate single crystals at elevated temperatures. Analysis of the chaotic state verifies the existence of a strange attractor, whose dimension and entropy are determined. The observations indicate a Ruelle-Takens-Newhouse scenario.

Picosecond optical parametric oscillator pumped by radiation from a continuously excited YAG:Nd3+laser

An experimental investigation was made of synchronous pumping of an optical parametric oscillator based on a barium sodium niobate crystal by trains of subnanosecond pulses from a YAG:Nd3+ laser which itself was continuously pumped. Pulses of ~10 psec duration were obtained in the wavelength range 0.8–1.6 μ and the efficiency of the conversion process was up to 25%.