LiTaO3 Crystal Research Articles

Biguanide, an Efficient Electrofreezing “Ice-maker” Ion of Supercooled Water

Following our previous investigations on the electrofreezing mechanism of supercooled water on pyroelectric crystal surfaces, we discovered that electrofreezing is a process involving the attraction and arrangement of specific ionic charges by an electric field. We found two classes of ions: the trigonal planar ions that raise the icing temperature, or “ice-makers”, and ions of different structures that reduce the icing temperature, or “ice-breakers”. In the search for more efficient promoters for electrofreezing, we anticipated that molecules that have the propensity to self-assemble with water to form hexagonal clusters might be better ice nucleators. Through icing experiments performed directly on the hemihedral faces of pyroelectric crystals of LiTaO3, we found that ions of biguanide elevate the icing temperature of supercooled water when concentrated near the negatively charged crystal’s interfacial water layer, either upon cooling or upon heating. On the other hand, the analogous guanylurea ions, which presumably assume configurations with deviations from planarity, operate as “ice-breakers”.

Charging characteristics of LiTaO3 crystals under irradiation with defocused electron beams of various energies

Main charging characteristics of LiTaO3 ferroelectric crystals under electron beam irradiation are presented. Experiments were carried out in a wide energy range of irradiating defocused electron beams. The main characteristics of the surface potential, the secondary electron emission current and the displacement current were found to be significantly different from those of classical dielectrics. Specifics of charging polarized ferroelectric crystals are due to the presence of a double layer of charges at the surface. We developed the four-layer charge distribution model which describes a superposition of the initial field and the electric field formed as a result of two-layer distribution of charges created under electron beam irradiation.

Quantum frequency conversion from ultraviolet to visible band through waveguides in a period-poled MgO:LiTaO3 crystal.

In research on hybrid quantum networks, visible or near-infrared frequency conversion has been realized. However, technical limitations mean that there have been few studies involving the ultraviolet band, and unfortunately the wavelengths of the rare-earth or alkaline-earth metal atoms or ions that are used widely in research on quantum information are often in the UV band. Therefore, frequency conversion of the ultraviolet band is very important. In this paper, we demonstrate a quantum frequency conversion between ultraviolet and visible wavelengths by fabricating waveguides in a period-poled MgO:LiTaO3 crystal with a laser writing system, which will be used to connect the wavelength of the dipole transition of 171Yb+ at 369.5 nm and the absorption wavelength of Eu3+ at 580 nm in a solid-state quantum memory system. An external conversion efficiency of 0.85% and a signal-to-noise ratio of greater than 500 are realized with a pumping power of 3.28 W at 1018 nm. Furthermore, we complete frequency conversion of the classical polarization state by means of a symmetric optical setup based on the fabricated waveguide, and the process fidelity of the conversion is (96.13 ± 0.021)%. This converter paves the way for constructing a hybrid quantum network and realizing a quantum router in the ultraviolet band in the future.

Etching mechanism of LiTaO3 crystals in CHF3/Ar plasma

CHF3/Ar plasma was used to etch LiTaO3 crystal by inductively coupled plasmas technique. X-ray photoelectron spectroscopy was performed to investigate the etching mechanism. It was found that chemical reactions had occurred between the F plasma and the Li and Ta metal species, forming the corresponding fluorides. Some fluorides are nonvolatile, and remained on the surface during the etching period. In order to get higher etching rate, it is important to remove these metal fluorides. The combination of chemical reaction and sputtered etching was performed and could effectively remove the remaining residues.

Q-switched mode-locked laser generation by Au nanoparticles embedded in LiTaO3 crystals

Au nanoparticles (NPs) in lithium tantalate (LiTaO3) crystal were prepared by ion implantation technique. The microstructure of the formed Au NPs was observed by transmission electron microscope (TEM). The linear and non-linear optical response of the samples was investigated and Z-scan measured that the Au NPs embedded LiTaO3 has saturable absorption properties. Based on this, the sample was used as a saturable absorber (SA) embedded in a waveguide laser system to achieve a 1 μm Q-switched mode-locked laser with a pulse width of 90 ps and a repetition frequency of 6.54 GHz.

Multi-resonant forward optical parametric oscillations without external mirrors based on nonlinear photonic crystals of LiTaO3

In this paper, we report experimental evidence of forward optical parametric oscillations (OPOs) with multi frequencies conversion processes in a spectral range of 400 nm–1700 nm using nonlinear photonic crystals of periodically poled LiTaO3 without external mirrors. The highly polished end-facets of the samples act as a Fabry–Perot cavity mirrors making the device simple and compact. Oscillation thresholds were found of 97.6 MW cm−2 and 160 MW cm−2 for the 1D and 2D samples, respectively. Moreover, at pump energies above the threshold, optical oscillations of multiple frequencies due to cascaded interactions established within the samples are obtained. In particular, we point-out the generation of two pairs of signal and idler (OPO1 and OPO2) in the same nonlinear photonic crystal. It is found that the second pair OPO2 appears with different quasi-phase matching conditions induced by a local refractive index variation. Our analysis indicates that this index variation results from a competing effect between quadratic cascading and electro-optic induced refractive index changes.

Photoelastic Properties of Trigonal Crystals

All possible experimental geometries of the piezo-optic effect in crystals of trigonal symmetry are studied in detail through the interferometric technique, and the corresponding expressions for the calculation of piezo-optic coefficients (POCs) πim and some sums of πim based on experimental data obtained from the samples of direct and X/45°-cuts are given. The reliability of the values of POCs is proven by the convergence of πim obtained from different experimental geometries as well as by the convergence of some sums of POCs. Because both the signs and the absolute values of POCs π14 and π41 are defined by the choice of the right crystal-physics coordinate system, we here use the system whereby the condition S14 > 0 is fulfilled (S14 is an elastic compliance coefficient). The absolute value and the sign of S14 are determined by piezo-optic interferometric method from two experimental geometries. The errors of POCs are calculated as mean square values of the errors of the half-wave stresses and the elastic term. All components of the matrix of elasto-optic coefficients pin are calculated based on POCs and elastic stiffness coefficients. The technique is tested on LiTaO3 crystal. The obtained results are compared with the corresponding data for trigonal LiNbO3 and Ca3TaGa3Si2O14 crystals.

Determination of optimal crystallographic orientations for LiNbO<sub>3</sub> and LiTaO<sub>3</sub> bimorph actuators

Abstract. The actuators for precise positioning based on bimorph structures of piezoelectric LiNbO3 and LiTaO3 crystals are considered. The optimal orientations of the actuator plates ensuring the highest possible displacements are determined by the extreme surfaces technique and the finite-element method. The simulated displacements for optimal orientations of LiNbO3 and LiTaO3 plates are compared with those obtained experimentally for manufactured LiNbO3 and LiTaO3 actuators, whose orientations are not optimal. As is shown, the optimal configuration of the actuator allows us to significantly increase its displacement for both LiNbO3 and LiTaO3 specimens.

A solidly mounted, high frequency, thickness shear mode bulk acoustic wave resonator using X-LiTaO3 thin plate and SiO2/Ta multilayer acoustic films

This paper describes a bulk acoustic wave (BAW) high-frequency resonator with a solidly mounted structure using a single crystal LiTaO3 (LT) thin plate. A Bragg reflector solidly supports the LT thin plate, which is fragile if self-suspended. The BAW resonator uses a thickness shear mode in 1.5 μm thick X-LT. The Bragg reflector is made of four pairs of SiO2 and Ta films, i.e. eight layers in total. The fabricated device works at a resonance frequency of 1.14 GHz and an antiresonance frequency of 1.23 GHz, showing a bandwidth of 7.9% and a low-temperature coefficient of frequency of −16 ppm °C−1 and −26 ppm °C−1 at the maximum and minimum admittances, respectively. The measured impedance ratio is 61 dB, although the structure and fabrication process are not optimized yet, suggesting a high potential for this device.

Ion irradiation induced strain and structural changes in LiTaO3 perovskite* *This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the

LiTaO3 crystals irradiated with 3 MeV and 1.162 GeV Au ions were studied by single crystal x-ray diffraction and Raman scattering measurements. The maximum lattice strains after 3 MeV Au ion irradiation to a fluence of 1.2 × 1013 cm−2 were 1.2% and 0.6% along the c- and a-/b-axes, respectively. Two effects were observed in 1.162 GeV Au ion irradiated samples: (i) the (0006) and (1120) Bragg peaks were split into doublets, which suggested a subtle structural change due to slight modification of chemical composition; and (ii) the pre-damaged 1.2% lattice strain along the c-axis was relaxed to 0.9% after subsequent irradiation with 1.162 GeV Au ions, while relaxation along the a- or b-axis was not obvious. A distinct change in the Raman spectrum of the 〈0001〉 oriented LiTaO3 crystals was observed after 1.162 GeV Au ion irradiation, but no obvious change was observed in the 〈1120〉 oriented samples or in 3 MeV Au ion irradiated samples. Strain and structural changes in crystalline LiTaO3, with or without pre-existing defects, upon ion irradiation are delineated in its responding to inelastic ionization and elastic nuclear collisions.

Reconstruction of depth resolved strain tensor in off-axis single crystals: Application to H+ ions implanted LiTaO3

In the context of growing interest in strain engineering, we present a theoretical protocol for the reconstruction of extrinsic and intrinsic strain tensors in single-crystals attached to a template, with an arbitrary oriented coordinate system. Input data for the protocol are extrinsic deformations of lattice planes, i.e., measured with reference to a template. By combining the protocol with elasticity theory, material property modification can be elucidated. Different methods for strain measurements can take advantage of this approach. It has been applied for reconstruction of strain tensor depth distribution in off-axis LiTaO3 crystals implanted with H+ ions, which is the key step for piezoelectric thin film-on-insulator fabrication by the Smart Cut process. Modifications of composition, lattice parameters, and elastic constants are indicated and discussed.

Effect of heavy ions irradiation on LiTaO3 crystal

In this work, congruent LiTaO3 crystals are irradiated by heavy ions Fe, Xe, and Bi respectively at fluence range of 1 × 1012 ~ 2 × 1015 cm−2. The effects of heavy ions irradiation are studied by using optical transmission spectroscopy, Rutherford backscattering, optical microscopy, X-ray diffraction.Heavy ion irradiation presents a unique effect in transmission spectra which is quite opposite to the previous reported results of light ions irradiation. The latter could often cause a significant optical absorption in visible light region. The former, however, not only induce no optical absorption, but can enhance transmittance over a broad spectral range (340–2500 nm). It is found that the discrepancy may originate from different damage process during ions irradiation. Light ion irradiation can create numerous of simple defects (like oxygen vacancies) serving as color centers which can cause an optical absorption. However, direct amorphization dominates the damage process induced by heavy ions, during which it hardly produces simple defects. Moreover, due to direct heavy ions bombardment, special textures are formed on the surfaces of the samples which serve as antireflection structures and enhance optical transmissions.

Calorimetric metal vapor adsorption energies for characterizing industrial catalyst support materials

Many important catalysts and electro-catalysts for energy and environmental technologies involve late transition metal atoms and nanoparticles dispersed across the surface of high-surface-area support materials, for example, oxide nanoparticles. The surface reactivity and long-term stability against deactivation of these materials depends strongly on the strength of bonding of the metal atom and nanoparticles to the support surface. Here, we introduce a novel calorimetry method that implements a LiTaO3 crystal for heat detection and extends metal adsorption calorimetry to surfaces of nanomaterials that are deposited from liquid solutions, as is typical when preparing industrial catalyst supports. This allows one to measure the strength of metal atom bonding and the adhesion energy of metal nanoparticles to clean surfaces of technologically relevant catalyst supports. We demonstrate that here by measuring the heat of Ag vapor adsorption onto the clean surfaces of high-surface-area TiO2 anatase powdered support materials (i.e., 5-nm-diameter nanoparticles). These heats of adsorption show a pulse-to-pulse standard deviation of only 9.3 kJ/mol (3.3%) for pulses containing only 1% of a monolayer of Ag vapor, with potential for a 5-fold reduction in noise if used with another metal evaporator. The calorimeter was also proven to work well measuring heats of Ag adsorption on calcium niobate (001) nanosheets deposited as thin films from liquid solution. This calorimeter opens up the possibility of using metal adsorption calorimetry to screen catalyst support materials for the strengths with which they bind metal atoms and metal nanoparticles, offering new opportunities to discover better support materials or for basic scientific study of structure / function relationships with respect to metal / support bond energies.

Latent Tracks in Ion-Irradiated LiTaO3 Crystals: Damage Morphology Characterization and Thermal Spike Analysis

Systematic research on the response of crystal materials to the deposition of irradiation energy to electrons and atomic nuclei has attracted considerable attention since it is fundamental to understanding the behavior of various materials in natural and manmade radiation environments. This work examines and compares track formation in LiTaO3 induced by separate and combined effects of electronic excitation and nuclear collision. Under 0.71–6.17 MeV/u ion irradiation with electronic energy loss ranging from 6.0 to 13.8 keV/nm, the track damage morphologies evolve from discontinuous to continuous cylindrical zone. Based on the irradiation energy deposited via electronic energy loss, the subsequently induced energy exchange and temperature evolution processes in electron and lattice subsystems are calculated through the inelastic thermal spike model, demonstrating the formation of track damage and relevant thresholds of lattice energy and temperature. Combined with a disorder accumulation model, the damage accumulation in LiTaO3 produced by nuclear energy loss is also experimentally determined. The damage characterizations and inelastic thermal spike calculations further demonstrate that compared to damage-free LiTaO3, nuclear-collision-damaged LiTaO3 presents a more intense thermal spike response to electronic energy loss owing to the decrease in thermal conductivity and increase in electron–phonon coupling, which further enhance track damage.

Tunable violet radiation in a quasi-phase-matched periodically poled stoichiometric lithium tantalate waveguide by direct femtosecond laser writing

We report on violet-light generation using the femtosecond-laser written waveguides in periodically poled MgO:LiTaO3 crystal under conditions of third-order quasi-phase matching. Ten parallel depressed cladding waveguides are successfully fabricated with different grating periods in the same sample with fan-out χ(2) grating structures. These waveguides exhibit high optical quality with minimum insertion loss as low as 0.71 dB. Temperature and wavelength tuned second harmonic generation for different waveguides are demonstrated by using a tunable CW Ti sappire laser. Tunable violet second harmonic light has been generated with a single period over the range of 396 nm to 401 nm by varying the crystal temperature from 60 °C to 200 °C. At the quasi-phase matching temperature, 0.37 mW of violet light power at 397.2 nm is generated for a fundamental power of 336.7 mW, corresponding to a normalized conversion efficiency of 0.39%/(W·cm2). Our work contributes to designing tunable and efficient on-chip violet light sources based on femtosecond-laser written waveguides.

Heterogeneous Electrofreezing of Super-Cooled Water on Surfaces of Pyroelectric Crystals is Triggered by Trigonal Planar Ions.

Electrofreezing experiments of super-cooled water (SCW) with different ions, performed directly on the charged hemihedral faces of pyroelectric LiTaO3 and AgI crystals, in the presence and in the absence of pyroelectric charge are reported. It is demonstrated that bicarbonate (HCO3 - ) ions elevate the icing temperature near the positively charged faces. In contrast, the hydronium (H3 O+ ) slightly reduces the icing temperature. Molecular dynamics simulations suggest that the hydrated trigonal planar HCO3 - ions self-assemble with water molecules near the surface of the AgI crystal as clusters of slightly different configuration from those of the ice-like hexagons. These clusters, however, have a tendency to serve as embryonic nuclei for ice crystallization. Consequently, we predicted and experimentally confirmed that the trigonal planar ions of NO3 - and guanidinium (Gdm+ ), at appropriate concentrations, elevate the icing temperature near the positive and negative charged surfaces, respectively. On the other hand, the Cl- and SO4 2- ions of different configurations reduce the icing temperature.

Heterogeneous Electrofreezing of Super‐Cooled Water on Surfaces of Pyroelectric Crystals is Triggered by Trigonal Planar Ions

AbstractElectrofreezing experiments of super‐cooled water (SCW) with different ions, performed directly on the charged hemihedral faces of pyroelectric LiTaO3 and AgI crystals, in the presence and in the absence of pyroelectric charge are reported. It is demonstrated that bicarbonate (HCO3−) ions elevate the icing temperature near the positively charged faces. In contrast, the hydronium (H3O+) slightly reduces the icing temperature. Molecular dynamics simulations suggest that the hydrated trigonal planar HCO3− ions self‐assemble with water molecules near the surface of the AgI crystal as clusters of slightly different configuration from those of the ice‐like hexagons. These clusters, however, have a tendency to serve as embryonic nuclei for ice crystallization. Consequently, we predicted and experimentally confirmed that the trigonal planar ions of NO3− and guanidinium (Gdm+), at appropriate concentrations, elevate the icing temperature near the positive and negative charged surfaces, respectively. On the other hand, the Cl− and SO42− ions of different configurations reduce the icing temperature.

Bidomain ferroelectric crystals: properties and prospects of application

Lithium niobate (LiNbO3) and lithium tantalate (LiTaO3) are among the most important and most widely used materials of coherent and nonlinear optics, as well as acoustics. High degree of uniformity and reproducibility has become the foundation of technology for manufacturing high-quality crystals, absorbed by many suppliers around the world. However, the above areas do not limit the use of LiNbO3and LiTaO3due to their unique piezoelectric and ferroelectric properties. One promising application of crystals is the design of electromechanical transducers for precision sensors and actuators. In this respect, the high thermal stability of the piezoelectric and mechanical properties, the lack of hysteresis and creep make it possible to create electromechanical converters with wide operating temperature range, that is beyond the capability of commonly used ferroelectric ceramics. The main advantage of LiNbO3and LiTaO3over other single-crystal piezoelectrics is ferroelectric domain structure regulation toward targeted impact on the device characteristics. One of the most striking examples of electromechanical transducer design through domain engineering is the formation of a so-called bidomain ferroelectric structure in crystal. It represents a single-crystalline plate with two macrodomains with opposite directions of spontaneous polarization vectors separated by a charged domain wall. High switching fields make inversion domains stable at temperatures up to 1000 °C. This review summarizes the main achievements in the formation of bidomain structure and near surface inversion domains in LiNbO3and LiTaO3crystals. We present the domain structure virtualization methods in crystals and non-destructive methods for controlling the domain boundary position. The report contains a comparative analysis of the methods for forming inversion domains in crystals, and the patterns and technological control methods of the domain structure are discussed. The basic physical models have been proposed in the literature to explain the effect of the inversion domains formation. In the present paper we outline what one sees as strengths and weaknesses of these models. The strategies of crystallographic cut selection to create devices based on bidomain crystals are briefly discussed. We provide examples of the implementation of devices based on bidomain crystals such as actuators, sensors, acoustic transducers, and waste energy collection systems.

Down- and up-conversion of femtosecond light pulses into Pr3+ luminescence in LiTaO3:Pr3+ single crystal

Spectra and decay curves of luminescence induced in a single crystal of LiTaO3:Pr3+ by femtosecond light pulses at different wavelengths from the UV-Blue and NIR regions were recorded and analyzed. It was found that excited levels involved in the broad UV absorption band of LiTaO3: Pr3+ are not able to relax via radiative transitions but they feed nonradiatively excited states of the ground Pr3+ configuration. Femtosecond pulse excitation in the NIR region results in an up-converted visible luminescence weakly affected by the pulse wavelength within the 1200 nm–1800 nm region. Spectra acquired imply that the supercontinuum (SC) generated does not promote single - or double-photon processes that may feed the 3P0 or 1D2 levels via transitions within the ground 4f2 configuration. It was concluded that the excitation mechanism is consistent with the multiphoton excitation (MPE) that feeds the 5d levels of Pr3+.

Robust second-order correlation of twin parametric beams generated by amplified spontaneous parametric down-conversion

We report an observation of the second-order correlation between twin beams generated by amplified spontaneous parametric down-conversion operating above threshold with kilowatt-level peak power, from a periodically poled LiTaO3 crystal via a single-pass scheme. Photocurrent correlation was measured because of the bright photon streams, with raw visibility of 37.9% or 97.3% after electronic filtering. As expected in our theory, this correlation is robust and insensitive to parametric gain and detection loss, enabling important applications in optical communications, precision measurement, and nonlocal imaging.