Effect In LiNbO3 Research Articles

Investigation of symmetry of photorefractive effect in LiNbO_3

The investigation of the light-induced changes of refractive index in a LiNbO(3): Fe sample in case of strip-like illumination is presented in the contribution. The changes of the refractive index are visualized by interferograms of the sample obtained for various orientation of the illuminated strip and various polarization of the light used during interferogram creation. The investigation shows that character of the dependences of the refractive index on the coordinate perpendicular to the illuminated strip is different for different strip orientation. It indicates the possibility that for different orientation of gradient of the illumination the different mechanisms are responsible for changes of the refractive index.

Combined Piezoelectrooptic Effect in Ferroelectric and Ferroelectric-Ferroelastic Crystals

The results of study of piezoelectrooptic (PEO) effect in the course of ferroelectric (Pb5Ge3O11) and ferroelectric-ferroelastic (Rochelle salt crystals) phase transitions are presented. It is shown that the temperature dependence of the combined PEO coefficients corresponds to the Curie-Weiss law. Basing on the studies for the combined PEO effects in LiNbO3 and LiTaO3 crystals, it is shown that the effect is interchangeable, i.e. its coefficients determined independently from the electrooptic and piezooptic experiments are the same. Large PEO effect is observed in LiNbO3 crystals, where electrooptic coefficient r22 increases almost two times after the action of mechanical stress σ 2 = 3.7× 10 5N/m2.

Light-induced acoustic effect in LiNbO 3 :Fe:Ce crystals

The phenomena of acoustic emission in LiNbO3:Fe:Ce crystals have been observed in the process of light-induced quasi-breakdown. It is found that the ultra-high frequency acoustic signal introduced into the crystal is modulated by the low frequency acoustic waves. Its frequency increases with the increase of the intensity of incident light and its jump period of breakdown is the same as that of the photovoltaic current Ic, the change of light-induced refractive index Δn and the diffracted light intensity L. This phenomenon has been analysed in this paper, which is caused by the inverse piezoelectric strain effect of the jump of space charge field during the quasi-breakdown.

Ferroelectric Based Pyroionization IR Converter

The characteristics of a noncoherent–coherent IR image converter that uses pyroelectric effect in LiNbO3 and the electro-optic effect and photorefraction in Bi12XO20 (X = Ti, Si, Ge) has been analysed theoretically and experimentally. An experimental multilayered structure by which IR radiation can be converted into coherent visible radiation was obtained on the basis of theoretical calculations. The measured threshold sensitivity of the converter, ∼ 10−5 W/cm2, was found to be comparable to theoretical estimates. The limiting resolution of the readout image was about 0.1 lp/mm. The change in the optical properties is estimated by use of the linear equation of an applied electric field (or polarization) that is not excessively strong.

Nephelauxetic effect in luminescence of Cr3+-doped lithium niobate and garnets

The model based on Harrison theory of bonding is used to explain quantitatively the nephelauxetic effect in LiNbO3 and Y3Al5O12 crystals doped with chromium, studied by high-hydrostatic pressure spectroscopy. The model uses only one adjustable parameter and can also be used for other dopant–ligands systems in different compounds. We show that not only ligands, but also the second neighbors of the dopant, influence the nephelauxetic effect.

Influence of the LiNbO 3 and KNbO 3 Seeds on the Sintering and Electrical Properties of PMN Ceramic

The effect of LiNbO 3 and KNbO 3 seeds on the microstructure and dielectric characteristics of PMN ceramic prepared by columbite route have been investigated with the addition of 0, 1, and 2-wt% of seeds. X-ray diffraction, Scanning Electron Microscopy and an impedance analyzer were used to characterize the influence of seeds on physical characteristics and dielectric properties of PMN. LiNbO 3 -seeded PMN samples present a significant increase in the amount of perovskite phase. The addition of LiNbO 3 seeds in sintered PMN ceramics at 1100@C during 4 h causes a decrease in the porosity and the amount of pyrochlore phase. Weight losses during sintering of PMN ceramics are suppressed more significantly for LiNbO 3 -seeded PMN. T m of PMN ceramics changes with seeds concentration. KNbO 3 seeds displace T m to lower temperature whereas LiNbO 3 causes its elevation. Dielectric constants of approximately 13,000 at 1 kHz was measured at m 5°C in PMN ceramics with 1-wt% of LiNbO 3 seeds.

The SHEW technique as a simple method to characterize the non-linear properties of crystals: investigation of helium implantation effects in LiNbO3 and KTiOPO4

Abstract The Second Harmonic wave generated with Evanescent Wave (SHEW) technique is first applied to measure the value of the non-linear coefficient, d 33 , of lithium niobate (LN). The result is in good agreement with the known value from the literature. We subsequently investigate the second-order optical properties of the near surface of He + -implanted LN and KTiOPO 4 (KTP) crystals. Our results show a rather strong degradation of the non-linearity (≈50%) in both crystals.

Study of the self-defocusing in LiNbO 3:Fe,Mg crystals

We present an experimental study of the photorefractive self-defocusing in LiNbO 3:Fe,Mg crystals which is investigated by using the Z-scan technique. The self-defocusing effect nonlinearity appears weak in LiNbO 3:Fe,Mg crystals. The experimental results show that self-defocusing is due to the photorefractive lens-like effect. The holographic recording and two-wave mixing are investigated in order to explain this effect in LiNbO 3:Fe,Mg crystals. We describe the principle and application of Z-scan technique, and analyze the single wavelength Z-scan measurements of the nonlinear absorption coefficient and the nonlinear refractive index and its sign of the samples LiNbO 3:Fe and LiNbO 3:Fe,Mg.

Electric field selectivity of reflection volume holograms in LiNbO 3

Theoretical and experimental investigations of electric field selectivity of reflection volume holograms in the geometry of the transverse electro-optic effect in LiNbO 3 are presented. The orientation of the LiNbO 3 allowing one to optimize the electric field selectivity has been found. Seventeen holograms were recorded in various electric fields, which demonstrates the efficiency of electric field multiplexing.

Comparison of photorefractive damage effects in LiNbO3, LiTaO3, and Ba1−xSrxTiyNb2−yO6 optical waveguides at 488 nm wavelength

Photorefractive-induced damage effects at 488 nm wavelength in LiNbO3, LiTaO3, and Ba1−xSrxTiyNb2−yO6 (BSTN) optical waveguides are compared for the extraordinary mode of polarization. The damage effects are strongest in LiNbO3 and weakest in BSTN. At an input power density of 3000 W/cm2, the output power from passive channel waveguide in LiNbO3 is more than 12 dB lower than in BSTN. Optically induced index changes measured using a Fabry–Perot interferometric method show a nonlinear behavior with increasing input intensity for all these materials. For incident power densities greater than 200 W/cm2 on the waveguides, the optically induced index-change damage increases at a rate of 2.8×10−3 cm2/μW in LiNbO3, 4.9×10−4 cm2/μW in LiTaO3, and 3.1×10−4 cm2/μW in BSTN.

Noise amplification mechanism in LiNbO_3:Fe crystal sheets

Based on a multiwave mixing model, we explain the symmetrical and broad light-induced scattering effect in LiNbO3:Fe crystal sheets. Analytical results are given in the undepleted-pumps approximation. The competition between forward small-angle scattering and climbing lights and its relation to the ratio of the size of the incident-light spot to the crystal thickness are discussed. The intensity angle distribution of the forward small-angle light-induced scattering is studied theoretically and experimentally. We suggest that the self-defocusing effect of the LiNbO3:Fe crystal plays an important role in the formation of the fanning intensity angle distribution.

High intensity illumination effects in LiNbO3 and KTiOPO4 waveguides

Quasi-phase-matched waveguides are known to degrade when generating high intensity short wavelength light. Photoinduced changes in the refractive indices can lead to reduced efficiency by broadening phase-matching curves or inducing power dependent losses. In this work a pump-probe technique was used to investigate photorefractive effects in nonlinear optical waveguides. A strong two photon photorefractive effect in single domain and Ti-poled LiNbO3 was found that is considerably reduced in electric field periodically poled LiNbO3 and is absent in Rb-exchanged KTiOPO4.

Picosecond Z-scan study of bound electronic Kerr effect in LiNbO 3 crystal associated with two-photon absorption

crystal have been measured using Z-scan technique with picosecond pulses at 532 nm. The nonlinear absorption coefficient and nonlinear refractive index are determined to be 2.5×10-10 cm/W and 5.3×10-15 cm2/W, respectively. Both sign and magnitude of the measured refractive nonlinearity are considerably different from the reported Z-scan results in LiNbO3 obtained with cw laser beam at 514 nm. The nonlinearities in LiNbO3 induced by 532 nm picosecond pulses are believed to be mainly due to two-photon absorption and bound electronic Kerr effect associated with the two-photon absorption.

Stark effect on Cr 3+ spectra in LiNbO 3

The electric field effect on the absorption spectra of Cr 3+ impurity centers in LiNbO 3 has been investigated at 77 K using a sensitive modulation method. A linear Stark effect on B- and R- absorption lines of Cr 3+ was observed for a field applied along the trigonal crystal axis Z, and no effect was detected when field was normal to Z. Such properties establish that the permanent dipole moments of the observed Cr 3+ centers are oriented along the trigonal crystal axis proving their C 3 point symmetry. The quantitative characteristics of the field effect are obtained. The marked peculiarity of the Stark effect in LiNbO 3 : Cr 3+ is the opposite sign of the electric field shift of B 1 and B 2 lines.

Electron paramagnetic resonance studies in photorefractive crystals I: Hyperfine interaction and photoinduced charge transfer in233U5+ and238U5+ doped LiNbO3

Electron paramagnetic resonance studies were conducted on the photoinduced charge transfer and also hyperfine interaction of U5+ stabilized in photorefractive matrix LiNbO3. This work deals with: (i) first observation of hyperfine structure due to233U (I=5/2) in its pentavalent state at octahedral sites and comparison with other possible site symmetries, (ii) photoinduced charge transfer as observable by EPR and its relevance to photorefractive behaviour of LiNbO3. The effect of chemical bonding on the hyperfine interaction of 5f1 configuration was also studied by converting the existing literature data on235U5+ to that of233U5+ by standard methods. This suggests that progressive substitution of oxygen by F−, in the series UO67−, (UO5F)6− and (UO4F2)5− drastically decreases the hyperfine coupling constantA∥, along the local distortion axis. This trend is explained as being due to the absence of ligand ion along the distortion axis at U5+ site in trigonal LiNbO3. The effects of illumination by copper vapor laser (CVL) on the intensity of the U5+ signal was studied in the 10–300K region. The kinetics of decay and restoration of U5+ was also studied between 10–100K range. The decay kinetics was found to obey double exponential. The reduction of concentration of U5+ with CVL-illumination and its restoration in the absence of light show that pentavalent uranium takes part in the photorefractive effects in LiNbO3.

Magnetophotorefractive effect in LiNbO_3:Fe crystals: theory and experiments

A theoretical and experimental analysis of the magnetophotorefractive effect for a vectorial holographic recording scheme is presented. Analytical expressions for the magnetic-field effect on space-charge field formation, two-wave coupling, and grating diffraction efficiency are given. A new, photovoltaic magnetic coupling vector that describes the magnetic-field dependence on grating formation is introduced. Good agreement with the theoretical predictions is found for new experimental results in the short time limit. These results show, for the first time to our knowledge, an enhancement of 60% of the diffraction efficiency caused by external application of a magnetic field with a magnitude of 0.2 T. The method provides a new all-optical technique for investigating the magnetophotovoltaic effect. Components of the magnetophotovoltaic tensor for crystals of LiNbO3:Fe are determined experimentally.

Observation of Optical Bistability in Two-Dimensional Volume Refractive Index Grating Thermally Fixed in LiNbO3:Fe Crystal

Experimental observation of optical bistability in a nonlinear two-dimensional volume refractive index grating is reported. The index grating in LiNbO3: 0.1 wt.% Fe photorefractive single crystal was fabricated by using hologram recording and subsequent thermal fixing techniques. Due to the thermal fixing, the stored 2D volume index grating shows no optical erasure during readout. An explanation of the nonlinear phenomena is also given in terms of the intensity-enhanced bulk photovoltaic effects in LiNbO3:Fe material.

Optical bistability and hysteresis in a two-dimensional periodic structure fabricated in Fe doped LiNbO 3

Optical bistability and hysteresis is observed experimentally with a nolinear two-dimensional (2D) periodic structure. The structure is a 2D volume index grating created in LiNbO 3:Fe crystal through hologram recording and subsequent fixing techniques. No external feedback is provided. A strong intensity-dependent photovoltaic effect in LiNbO 3:Fe material provides nonlinear coupling for the excited fields within the 2D periodic structure.

Stress induced domain formation in LiNbO3 single crystals

The domain formation phenomenon of LiNbO3 crystals was investigated in this study. A stress induced domain formation mechanism was proposed, and domain formation of the as-grown crystals and domain inversion of substrate crystals were explained. The strong piezoelectric effect of LiNbO3 at elevated temperature, could be the direct driving force for inversion of the spontaneous polarization direction and could form domain walls. It was found that the tensile component of the internal stresses can inverse the original direction of the spontaneous polarization.

Extraordinary-mode refractive-index change produced by the linear electro-optic effect in LiNbO_3 and reverse-poled LiNbO_3

To examine aspects of an integrated photonic electric-field sensor, we calculate electro-optically induced refractive-index change in regular and reverse-poled LiNbO(3). Specifically, for y-propagating extraordinary modes, we determine how index change depends on electric-field magnitude and direction. To accomplish this, changes in index-ellipsoid shape and orientation are found by the use of a numerical eigenvalue procedure to diagonalize the impermeability tensor; then, refractive index is calculated by the use of a vector reference-frame transformation and a small perturbation approximation. A general formula is inferred from calculations for specific field directions. Electro-optic coefficients for reversepoled LiNbO(3) are obtained by application of a tensor reference-frame transformation to those of LiNbO(3). The index-calculation procedure has utility beyond the problem that is considered.