Niobate Crystals Research Articles

Effect of thulium impurity on the dielectric properties of barium strontium niobate single crystals

This paper presents the results of a study of the dielectric response in single crystals of barium strontium niobate doped with thulium of various concentrations. It is shown that the dielectric permittivity increases with increasing concentration of thulium. For as-grown samples the dispersion of the permittivity is observed in the frequency region of 106 Hz. The dependence is not observed for the samples polarized under DC field. For all the samples studied, the switched polarization increases and the coercive field decreases under action of an AC field.

Observation of Neutron-Induced Absorption and Phase-Mismatch for Quasi-Phase-Matched Second Harmonic Generation in Congruent Lithium Niobate

We report an experimental observation of radiation-induced optical absorption in undoped congruent lithium niobate (LiNbO3) crystals between the 190 nm and 3200 nm wavelength range. It was found that high-dose (up to 288 Gy) gamma rays did not significantly affect the optical absorption of LiNbO3 during that wavelength range. However, upon the order of 1016 cm−2 neutron irradiation, the change in the absorption coefficient was up to 0.6 cm−1 at a wavelength of 532 nm and remained after 13 days in the dark at room temperature. The nonlinear optical performance was characterized by conducting third-order quasi-phase-matched second harmonic generation in neutron-irradiated periodically-poled LiNbO3, showing that the phase-matching condition was altered, and the conversion efficiency was still comparable with a non-irradiated one.

Quasi-CW Pumping of a Single-Frequency Fiber Amplifier for Efficient SHG in PPLN Crystals with Reduced Thermal Load

Single-frequency lasers are essential for high-resolution spectroscopy and sensing applications as they combine high-frequency stability with low noise and high output power stability. For many of these applications, there is increasing interest in power-scaling single-frequency sources, both in the near-infrared and visible spectral range. We report the second-harmonic generation of 670 µJ at 532 nm of a single-frequency fiber amplifier signal operating in the quasi-continuous-wave mode in a 10-mm periodically poled Mg-doped lithium niobate (MgO:PPLN) crystal, while increasing compactness. To the best of our knowledge, this is the highest pulse energy generated in this crystal, which may find applications in the visible and UV such as remote Raman spectroscopy.

Targeted Changes in the Optical, Electronic, and Elastic Characteristics of Undoped and Doped Crystals of Lithium Niobate

Targeted Changes in the Optical, Electronic, and Elastic Characteristics of Undoped and Doped Crystals of Lithium Niobate

Thermodynamic Study of Adsorption Capacity between Metal Film and Optical Crystal: Adsorption Energy of Ni Films on LiNbO3 Substrates

The growth of large areas of two-dimensional homogeneous graphene depends on the bond between the metal film, which acts as a catalyst, and the substrate material. The structural differences between the metal and the various anisotropic crystals make this growth method a challenge for the feasibility of growing graphene on optical crystals. In this paper, the evolution of the adsorption energy between nickel (Ni) films and Lithium Niobate (LiNbO3, LN) crystals is modelled under different thermal treatment environments by constructing a physical model of the temperature dependence of the adsorption energy between the two materials. With the aid of a series of simulated full annealing processes, the changes in adsorption energy at different temperatures were calculated. The results show that there are two “temperature windows” with target annealing temperatures of 700–800 K and 950–1050 K that prove to have high adsorption energies. This is of great guiding and practical significance for the direct transfer-free synthesis of graphene on LiNbO3 substrates.

An Optical Parametric Oscillator in the Mid-IR Range Based on a Fan-out Periodically Poled Structure of Lithium Niobate with a Narrow-Band Seeding Laser

The results of experimental studies of the effect of narrow-band seeding radiation of a gas laser on the spectral width of the oscillation line of an optical parametric oscillator (OPO), which is based on a fan-out structure of a periodically poled lithium niobate (PPLN) crystal, are presented. The use of a seeding He–Ne laser made it possible to reduce the generation threshold for the OPO by a factor of 1.53, from 120 μJ (29.5 mJ/cm2) to 78 μJ (19 mJ/cm2). When the modes of the He–Ne laser were optimally matched in the OPO cavity, the width of the spectral line of the signal wave decreased by a factor of 4.65 and equaled 0.481 nm.

Evolution of the domain structure during polarization reversal in relaxor SBN single crystals studied by Čerenkov-type second harmonic generation microscopy

The evolution of the domain structure during polarization reversal in single crystals of a relaxor ferroelectric strontium-barium niobate (Sr0.61Ba0.39Nb2O6) doped with 0.05 wt.% Ni2O3 was investigated. The domains in the crystal bulk were imaged by Čerenkov-type second harmonic generation microscopy. Three types of domains were revealed: (1) domains with a broad boundary, (2) cylindrical domains, and (3) conical domains. Three stages of the domain shape evolution were distinguished in the domain with a broad boundary. The velocities of the sideways wall motion and forward domain growth were measured for all the domain types.

Measurement of the absorption coefficient of a periodically poled LiNbO3 crystal at a radiation wavelength of 3 μm

Problem formulating. In the case of nonlinear-optical conversion of high-power laser radiation in nonlinear-optical crystals the optical absorption leads to a nonuniform heating of the crystals, which results in the violation of phase matching conditions, the formation of defects, and optical damage. Goal. Measurements of optical absorption coefficient of the periodically poled lithium niobate (PPLN) crystal at 3 μm radiation wavelength using the piezoelectric resonance laser calorimetry (PRLC). Result. The optical absorption coefficient of PPLN crystal at 3.045 μm radiation wavelength was measured using the piezoelectric resonance laser calorimetry. The value (1.15±0.15) 10⋅ -2cm-1 of absorption coefficient within the measurement error limits was independent of the initial temperature of PPLN and the incident radiation power in the ranges 293–343 K and 0.2–10 W respectively. Practical meaning. The interaction of mid-IR laser radiation with PPLN crystal was studied using the piezoelectric resonance laser calorimetry.

Selection of the Material for the Sensitive Elements of SAW-based Accelerometers

Introduction. At the present, sensors based on surface acoustic waves (SAW) is a rapidly developing direction and a promising replacement for classical sensors, especially in those areas where long-term performance of latter is questionable. The principle of operation of SAW sensors is based on acoustic vibrations, therefore, the choice of piezoelectric material of а console, considering external influences on a future device and its operating conditions, is the most important task. Currently, many monocrystalline structures and their sections have been synthesized and created for the devices using SAW. The main materials used for the manufacture of substrates are crystals of quartz (SiO2), lithium niobate (LiNbO3), lithium tantalate (LiTaO3) and film aluminum nitride (AlN). Also, new crystal structures: langasite (La3Ga5SiO14), langatate (La3Ga5.5Ta0.5O14), langanite and others were produced. The problem of using such materials for the manufacture of consoles is the lack of systematized data on important characteristics for the propagation of surfactants, for example, the elasticity tensor of the 4th rank. One of the key problems for the further development of SAW-based sensors is the one-way fastening of rectangular and triangular sensitive elements (SE) in sensor housing. In order to overcome the above drawback an MMA surfactant thing based on a membrane SE for a more uniform distribution of a load over the surface of the SE was proposed.Aim. To show the advantages of using AlN as the SE material of a ring wave resonator on SAW.Materials and methods. The theoretical part of the research was carried out using the finite element method. Mathematical processing was implemented in AutoCAD 2019 and in COMSOL Multiphysics 5.4.Results. The use of AlN, which acts as the SE material for measuring an acceleration based on SAW was proposed. The proposed solution was compared with existing prototypes based on the use of SiO2 / LiNbO3 membranes, which were characterized by strong anisotropic properties. A 3D model of the SE of a ring wave resonator on surface waves was created. Using computer simulations and COMSOL Multiphysics software, it was shown that the thing was capable to withstand exposures in excess of 10 000 g, and an isotropic AlN sensor overcomed the limitations of both the low sensitivity of SiO2 and the low temperature stability of LiNbO3. AlN demonstrated almost double resistance to irreversible mechanical deformations as compared to SiO2, which, in turn, allows an additional 1.5-fold increase in sensitivity compared to quartz – based sensors.Conclusion. Based on the data obtained by the modeling, it can be concluded that the use of AIN as SE material is promising, especially for measuring high acceleration values, but with restrictions on temperature sensitivity of the material.

Domain shapes in bulk uniaxial ferroelectrics

We considered the experimentally observed variety of domain shapes in crystals of lithium niobate and lithium tantalate family. The shapes were classified, and their formation was discussed in terms of the universal kinetic approach to the domain growth using step generation and kink motion processes basing on analogy with crystal growth. The screening retardation resulting in step generation at the vertices of the polygonal domains under the action of the spatially nonuniform local electric field was considered. The domain shape field dependence was explained by simulated field distribution and difference between the threshold fields for step generation and kink motion.

Visualization of Optical Uniformity Alloyed Single Crystals of Lithium Niobate

It was shown that laser conoscopy can visually detect even slight changes in the optical characteristics of a crystal when it is doped. It has been found that the defective structure of LiNbO3:Zn (4.5 mol. %), LiNbO3:Mg (3.0–5.5 mol.%) crystals associated with an uneven entry of an impurity leads to a local change in the elastic characteristics of the crystal and the appearance of mechanical stresses that distort the conoscopic patterns. This can be an abnormal optical biaxiality, which manifests itself in the form of a rupture and enlightenment of the "Maltese cross" in the center of the conoscopic crystal pattern, or local birefringent inclusions that are recorded as additional interference patterns against the background of the main conoscopic pattern, both in the center of the field of view and in its peripheral area.

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.

Local polarization reversal in 36° Y-cut congruent lithium niobate by focused electron beam: forward domain growth

The growth of requirements to frequency mixers adapter for high-power lasers stimulates the studies of domain kinetics in nonlinear ferroelectric crystals with the slanted polar axis. Forward domain growth after local polarization reversal by focused electron beam irradiation and domain interaction were studied in 0.5-mm-thick 36° Y-cut crystals of congruent lithium niobate. The dependences of domain length on the distance between domains and position in a block of domains were explained by the distribution of the space-charge field and domain–domain interaction. The stripe domains with length up to 500 µm were produced.

Holographic measurement of surface acoustic wave parameters in crystals

The theoretical basis of a specialized technique for applying digital holographic interferometry to measure the parameters of surface acoustic waves is presented, a measuring system for visualization and quantitative analysis of the parameters of ultralow-amplitude high-frequency oscillations arising in electronic devices using surface acoustic waves is developed, and experimental results of the study of surface acoustic waves in crystals of lithium niobate are obtained. In this case, to ensure the possibility of recording precision double-exposure interferograms of high-frequency surface acoustic waves, a picosecond pulsed laser with two-stage frequency multiplication was used as a radiation source, and to increase the spatial resolution of the system with the possibility of observing a wide field of view, an adjustable optical zoom of the incoming image was applied to the matrix input (based on charge-coupled devices) of the recording camera and digital zoom was used for obtained interferogram. We achieved the measuring sensitivity of the surface acoustic waves amplitude and spatial-temporal resolution allowing visualization and measurement of surface acoustic waves with amplitudes of the order of 1 nm and frequencies of the order of 10 MHz, which is far beyond the capabilities of standard methods of holographic interferometry.

Growth and Thermal Properties of Mg-Doped Lithium Isotope Niobate (Mg:7LiNbO3) Crystal

An Mg-doped isotope lithium niobate (Mg:7LiNbO3) crystal was successfully grown from 7LiOH, Nb2O5, and MgO using the Crozchralski method. The weight of the as-grown crystal with good quality was about 40 g. The crystal structure was determined as an R3c space group using the X-ray powder diffraction (XRPD) method, and the crystal composition (Li%) determined using the Raman mode linewidth method was 49.29%. The average transmittance of the crystal in the range of 500–2500 nm was approximately 72%. Various thermal properties, including the specific heat (Cp), the thermal expansion coefficient (α), the thermal diffusion coefficient (λ), and the thermal conductivity (κ), were carefully determined and calculated, and the value divergences among Mg:7LiNbO3, the undoped isotope lithium niobate (7LiNbO3), and natural lithium niobate (LiNbO3) crystals were mainly related to the differences in microstructure caused by the crystal composition.

Effect of Nanoscale Defects on the Physical Properties of Lithium Niobate and Lithium Tantalate Crystals

The elastic, ferroelectric, and transport properties of congruent lithium niobate and lithium tantalate crystals are studied in the temperature range of 77–450 K, depending on the conditions for recovery annealing. Significant changes in the elastic moduli and electrical conductivity that correlate with an increase in the displacement of the off-center Nb5+ (Ta5+) ions along the trigonal $$\overline C $$ axis of the oxygen octahedra NbO6 (TaO6) are found in the interval 120 to 300 K as a result of more detailed studies. The attenuation of acoustic waves is suppressed as the temperature falls, which can be explained by an increase in the degree of ordering of NbO6 (TaO6) clusters. It may be assumed that the strong change in electrical conductivity correlates with the concentration of point nanoscopic defects (antisite defects Nb Li 5+ (Ta Li 5+ ), coupled polarons Nb Li 4+ (Ta Li 4+ ), and bipolarons).

Contribution from structural Jahn–Teller ions to the elastic and ferroelectric properties of lithium niobate and lithium tantalate

Elastic and ferroelectric characteristics of single crystals of lithium niobate and tantalate are investigated in a wide range of temperatures by complex acoustooptic means. The contribution from Jahn–Teller NbO6 and TaO6 systems to the characteristics of elastic moduli, ultrasonic attenuation, and nonlinear optical coefficients is analyzed using a new phenomenological model. It is hypothesized that the displacement of Nb5+ and Ta5+ ions, which exhibit the second-order Jahn–Teller effect along trigonal axis C, and the subsequent ordering of octahedral, result in unusual elastic and ferroelectric properties.

Growth of isolated domains induced by focused ion beam irradiation in congruent lithium niobate

ABSTRACTFormation of isolated domains induced by i-beam irradiation in single crystals of congruent lithium niobate with polar surface covered by uniform resist layer was studied. The change of domain shape with dose increase was attributed to gradual penetration of charge through the resist layer caused by i-beam milling. The appearance of the dendrite structures was attributed to formation of the surface dielectric gap due to out-diffusion of oxygen to electrode. We applied the obtained knowledge for creation of the 1-µm-period 2D square arrays of isolated domains with minimal radius about 300 nm and the 1-µm-period 1D pattern of stripe domains.

Spectral-luminescent properties of gradient-activated LiNbO3 crystals with concentration profiles of Yb3+ and Er3+ ions

The luminescent properties of gradient-activated crystals of lithium niobate with concentration profiles of optical centers, ytterbium and erbium ions, are studied. It is shown that the spectral-luminescent properties of the gradient crystals are correlated with the concentration profiles of optical centers — donors Yb3+ and acceptors Er3+.

IR absorption spectra in the region of stretching and deformation vibrations of hydrogen bond in pure and alloyed single crystals of LiNbO3

We have measured infrared absorption spectra of the stretching and bending vibrations of the hydrogen bond of pure and alloy additives Me (Me = Mg, Zn) single crystals of lithium niobate (LiNbO 3 ) grown using various technologies. Preliminary studies of the spectra showed that the frequency of stretching vibrations in the IR spectra of single-crystal samples obtained from the homogeneously doped charge differ significantly (more than 50 cm −1 ). However, no difference in the IR spectra of single crystals obtained using other doping techniques, we have found. It is assumed that the observed differences in the absorption spectra of single crystals due to the different character of the formation of hydrogen bonds in the preparation of precursors Nb 2 O 5 : Me.