Potassium Lithium Tantalate Niobate Research Articles

Controlled composition modulation in potassium lithium tantalate niobate crystals grown by off-centered TSSG method

Off-centered top-seeded solution growth (TSSG) method is demonstrated as an effective and simple way to generate controlled composition modulation in potassium lithium tantalate niobate (KLTN) single crystals. The changes in concentration were measured by differential interference contrast (DIC) microscopy. Large length with periodic modulations ranging from 1 to 5 μm in period was grown along a KLTN sample with period dispersion lower than 2%.

Czochralski growth and constitutional studies on single crystals of potassium lithium niobate (KLN)

AbstractThe ferroelectric phase of potassium lithium niobate K3Li2−xNb5+xO15 (KLN) is a very promising material for the conversion of infrared light to light in the visible region. However, growing of single crystals is known to be complicated due to the considerable anisotropy of the growth rate and the thermal expansion behaviour. The single crystals of KLN, Mg2+‐doped KLN, as well as the mixed crystals of potassium lithium tantalate niobate K3Li2(Nb1−xTax)5O15 (KLTN) were grown by the Czochralski technique. The chemical analyses of the samples were performed by atomic absorption spectroscopy (AAS) and X‐ray fluorescence analysis (XRF). The element concentrations along the single crystals were measured by the electron microprobe analysis (EMPA) to clarify the segregation phenomena in the grown crystals. The elements distribution coefficients were also calculated. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Soliton-based Y-branch in photorefractive crystals induced through dispersion-shifted optical fiber.

We experimentally demonstrate for what is believed to be the first time that a dispersion-shifted fiber can be used to electro-optically induce a soliton Y-branch structure in a photorefractive centrosymmetric paraelectric crystal (potassium lithium tantalate niobate). The application of a nonstationary external bias field enables us to stabilize the spatially partially coherent behavior of the optical beam at the fiber output. Furthermore, we show the switching capabilities of this soliton-based device in the optical communication field guiding a probe beam at a nonphotorefractive wavelength (1557 nm).

Electro-optic beam manipulation through photorefractive needles

We demonstrate electro-optic spatial two-dimensional mode switching in a bulk sample of potassium lithium tantalate niobate. Spatial confinement, mode coupling, and electro-optic functionality are mediated by two photorefractive needle solitons of opposite electroholographic charges embedded together in their anisotropic lobular structure.

Growth, etching, polarization and second harmonic generation of potassium lithium tantalate niobate crystals

Potassium lithium tantalate niobate K 3Li 2(Ta x Nb 1− x ) 5O 15 crystal was grown by top-seeded solution growth method. Crack-free crystal in a size of 4×5×15 mm 3 was obtained. The as-grown crystal was demonstrated to be in a multidomain state by chemical etching. Single domain crystal was obtained by applying a DC electric field at an elevated temperature. The crystal was used to double the frequency of 1.06 μm of the Nd : YAG laser at room temperature by non-critical phase matching.

Formation of metastable ferroelectric clusters inK1−xLixTa1−yNbyO3:Cu,Vat the paraelectric phase

We present experimental evidence indicating that in potassium lithium tantalate niobate at the paraelectric phase, ferroelectric clusters are formed to compensate the space charge induced field created in a photorefractive process. These clusters are distributed in a slow spontaneous process and form a dipolar grating which is spatially correlated with the photorefractive space charge grating. By investigating the Gibbs free energy, we show that the compensating gratings are formed only in the temperature region where a metastable ferroelectric state is allowed to exist at the paraelectric phase. The compensation process, as well as its temperature and electric field dependence are interpreted in terms of the Gibbs free energy.

Two-dimensional photorefractive spatial solitons in centrosymmetric paraelectric potassium–lithium–tantalate–niobate

We report the observation of steady-state two-dimensional photorefractive self-trapping and screening spatial soliton formation in a sample of potassium–lithium–tantalate–niobate in the centrosymmetric paraelectric phase.

Dipolar holographic gratings induced by the photorefractive process in potassium lithium tantalate niobate at the paraelectric phase

We present experimental evidence indicating the formation of dipolar holographic gratings in potassium lithium tantalate niobate at the paraelectric phase slightly above the phase transition. These gratings are formed in the dark, following the writing of space-charge-based photorefractive gratings, under an external electric field. The dipolar gratings create a spatial modulation of the low-frequency dielectric constant, and the latter induces a spatially correlated modulation of the polarization, which is transformed into birefringence gratings through the quadratic electro-optic effect.

Holographic gratings by spatial modulation of the Curie-Weiss temperaturein photorefractiveK1−xLixTa1−yNbyO3:Cu,V

We present experimental evidence indicating the formation of metastable dipolar gratings in potassium lithium tantalate niobate at the paraelectric phase. These dipolar gratings result from the formation of local metastable changes in the Curie-Weiss temperature, which, in the presence of an external electric field, induce changes in the low-frequency polarization. The polarization changes create spatially correlated birefringence gratings due to the electro-optic effect. The dipolar gratings are formed in a slow spontaneous process, to compensate for regular photorefractive gratings immediately after the creation of the latter.

Ferroelectric domain gratings and Barkhausen spikes in potassium lithium tantalate niobate

The observation of Barkhausen current spikes during the recording of volume phase holograms in potassium lithium tantalate niobate is reported on. These spikes are due to the ferroelectric domain reversal induced by photorefractive space charge fields. Both “small” (1 nA) and “large” (100 nA) spikes are observed, which correspond to micro and macro domain reversal, respectively. The diffraction efficiency can change as much as 50% during a single macrodomain switching.

Copper, hydrogen, and titanium incorporation in potassium lithium tantalate niobate single crystals

In this study we propose a model that describes the diffusion of copper, hydrogen, and titanium through the liquid/solid interface in potassium lithium tantalate niobate crystals. Copper and hydrogen ions may occupy potassium/lithium vacant sites. Hydrogen ions are also able to stay at tantalate/niobate vacant sites in the presence of titanium. This model shows that the hydrogen concentration can be dramatically reduced in KLTN:Cu,X,Ycrystals (where X, Yare any first row transition metals but not Ti or Cu), and is in agreement with experimental results.

Fixing of volume holograms in ferroelectric K_1−yLiyTa_1−xNbxO_3

We report on the fixing of photorefractive volume holograms in potassium lithium tantalate niobate with ionic gratings and also with ferroelectric domain-reversed gratings. A diffraction efficiency of 55% is obtained with domain reversal in a 2-mm-thick ferroelectric phase K(1-y)Li(y)Ta(1-x)Nb(x)O(3) crystal doped with Co, V, and Ti. We measured the decay rate of the domain gratings and also of the initial electron gratings and ion gratings. The domain grating decay agrees with Vogel-Fulcher fits. The activation energies for ionic and electronic conductivity are 0.76 and 0.12 eV, respectively.

Electroholographic neurons implemented on potassium lithium tantalate niobate crystals

We describe a new approach for constructing large-scale artificial neural networks. The novelty of our approach is based on the concept of electroholography (EH), which permits interconnecting of electronic neurons by minute-volume holograms, using the voltage-controlled photorefractive effect in paraelectric crystals. Crystals of potassium lithium tantalate niobate (KLTN) in the paraelectric phase are shown to be suitable for implementing this concept. A small network composed of two KLTN crystals on which holographic connections are recorded is presented to demonstrate the EH approach.

Growth and characterization of K3Li2(TaxNb1−x)5O15 crystals for blue second-harmonic-generation applications

Potassium lithium tantalate niobate, K3Li2(TaxNb1−x)5O15, or KLTN single crystals were grown by spontaneous crystallization method, and it has been demonstrated that the KLTN crystal has high potential as a nonlinear crystal for blue second-harmonic-generation (SHG) applications. Ta substitution for Nb site in K3Li2Nb5O15 crystal improves the transparency in the blue light region and decolorizes the material. Compared with K3Li2Nb5O15, the K3Li2Ta5O15 crystal exhibits a 60 nm blueshift of the absorption edge from 376 to 316 nm, and decreases its absorption coefficient from 2.3 to 0.3 cm−1 at 400 nm. The phase-matched frequency doubling of the Ti:sapphire infrared laser for blue SHG at room temperature has been demonstrated with the KLTN bulk crystal.

Self-pumped phase conjugation of KLTN crystal

Potassium lithium tantalate niobate (KLTN) crystals were grown using the flux pulling method. The two-wave mixing gain coefficient of a KLTN:Fe crystal was measured to be 2.7 cm −1. Using this crystal, a “cat” self-pumped phase conjugator has been demonstrated, for the first time. A reflectivity of 14% and a response time of the phase conjugator of 3 s at 3 W/cm 2 was measured using a frequency-doubled Nd:YAG laser.

Growth and characterization of the perovskite K 1- yLi yTa 1- xNb xO 3:Cu

We report the growth of doped potassium lithium tantalate niobate (KLTN) crystals and characterization of their physical properties. The top seeded solution growth method is described. The specifics of a particular KLTN:Cu growth are presented, and the resultant crystal is described. The dielectric properties are compared to those of KTN; the addition of lithium is demonstrated to change the character of the phase transitions as well as increase the transition temperature. Phase diagrams for the KLTN system are illustrated as a function of lithium and niobium concentration.

Simple methods of measuring the net photorefractive phase shift and coupling constant

We report measurements of the photorefractive phase shift and coupling constant of several photorefractive materials. We solve the problem of beam coupling and diffraction in a material with a dynamically written grating for arbitrary input beams. These solutions are used to determine the beam coupling as a function of the photorefractive phase ø and coupling constant g when one beam is either sinusoidally phase modulated or ramped in phase. Experimental results are obtained for LiNbO(3), BaTiO(3), and for paraelectric potassium lithium tantalate niobate as a function of applied electric field.

KLTN Self-Pumped Phase Conjugation

AbstractHomogenous tetragonal potassium lithium tantalate niobate (KLTN) crystals were grown using the flux pulling method. A two-wave-mixing gain coefficient of 0.5cm−1 has been measured using undoped KLTN. The gain coefficient can be increased to 2.7 cm−1 after doping of 0.2wt% Fe. The “cat” self-pumped phase conjugator was performed, for the first time, with KLTN:Fe crystal. We obtained a reflectivity of 14% and a response time less than 3 seconds using a frequency-doubled Nd:YAG quasi-continuous laser.

Characterization of a new photorefractive material: K_1−yLyT_1−xNx

We report the growth and characterization of a new photorefractive material, potassium lithium tantalate niobate (KLTN). A KLTN crystal doped with copper is demonstrated to yield high diffraction efficiency of photorefractive gratings in the paraelectric phase. Voltage-controllable index gratings with n(1) = 8.5 x 10(-5) were achieved, which yielded diffraction efficiencies of 75% in a 2.9-mm-thick sample. In addition, diffraction was observed in the paraelectric phase without an applied field. This effect is attributed to a growth-induced strain field.