LiTaO3 Crystal Research Articles

Measuring of the surface acoustic wave amplitude in the X-112° Y-cut of a LiTaO3 crystal using X-ray diffraction at the laboratory X-ray source

The SAW excitation and propagation on the X-112° Y-cut of a LiTaO3 crystal were studied using a triple-axis X-ray diffractometer with a laboratory X-ray source. Simulation of X-ray rocking curves with the Takagi equation system enabled the determination of surface acoustic wave amplitudes on the crystal surface. The SAW excitation process in the frequency range of an acoustoelectronic device, determined by the excitation band or interdigital transducer structure, was studied.

Optimization of transverse electro-optic effect in LiNbO3 and LiTaO3 crystals

Optimization of transverse electro-optic effect in LiNbO3 and LiTaO3 crystals

Influence of Parameters in Vapor Transport Equilibration Treatment on Composition and Homogeneity of LiTaO3 Single Crystals

The effect of key parameters such as time, temperature, and equilibration powder concentration in vapor transport equilibration (VTE) treatment on the Li2O content of initially congruent X‐, Y‐, and Z‐cut LiTaO3 crystals is experimentally investigated. The Li2O content across the thickness of the crystal is estimated by Raman spectroscopy with accuracy of 0.05–0.15 mol%. The Li2O loss from equilibration powders has been monitored as a function of treatment temperature and duration. The results show that the Li2O content in the crystal nonlinearly depends on the equilibration powder composition and that homogeneous stoichiometric LiTaO3 crystals can be obtained by treatment for at least 36h at 1250°C in Li2O‐rich atmosphere, created by powders containing >54 mol% of Li2O. The anisotropic Li+ diffusion coefficients and its activation energy are also experimentally estimated. Finally, the VTE conditions are defined for the production of different cuts of LiTaO3 crystals with controlled homogeneous Li2O nonstoichiometry in the range from subcongruent to stoichiometric compositions.

Conical quasi-phase-matching second harmonic generation in a 2D photonic crystal with hybrid Ewald geometric method

The direction variation of the fundamental wave in the same nonlinear photonic crystal would cause different pattern of harmonics generation. In a 2D/3D crystal with dense reciprocal lattice vectors, there will be large numbers of conical harmonic beams evolving with direction change of the fundamental wave. By rearranging the Ewald sphere and superposing it into the Ewald shell, we have a hybrid Ewald construction. It becomes a simple but useful geometric method to comprehensively depict the distribution of these quasi-phase-matching second harmonics and their conical form evolution. It presents conical second harmonic beams by their related reciprocal lattice vectors and simplifies the beams’ distribution according to spatial arrangement of those reciprocal lattice vectors. It finds that the conical beams will create, annihilate, or get enhanced in specific order when fundamental waves change incident directions. We applied the method on a periodically poled 2D LiTaO3 crystal and all observed phenomena, meet the method’s predictions. In our experiment, we observed that the conical beams distorted along the optic axis of the sample due to anisotropy, which was generally overlooked by earlier researches. The eccentricities of their ring projections suggest a potential auxiliary approach for crystal dispersion measurement.

The influence of the volume concentration of hydrogen on the fine structure of the IR absorption spectra and conductivity features in congruent LiTaO3 crystals

A new method for changing the volume concentration of hydrogen in congruent LiTaO3 (lithium tantalate, LT) crystals has been studied. It has been established that pre-treatment of the sample in adipic acid significantly increases the volumetric concentration of hydrogen in the sample during subsequent annealing in a humid atmosphere at a relatively low annealing temperature. First of all, this preserves the LT single crystal in a single-domain state. In contrast to known methods for increasing the volumetric concentration of hydrogen, the proposed method affects the absorption coefficient of the sample in the optical range less than for a congruent LiNbO3 crystal. It has been shown that the type of IR absorption spectrum of OH− groups and the defect structure of the LT crystal significantly depend on the volume concentration of hydrogen in the sample. The study also analyzed the reasons for this effect. The temperature dependences of the electrical conductivity of LT samples with different hydrogen concentrations have been studied. It has been shown that the type of electronic conductivity of LT samples changes when the concentration of OH groups in the crystal increases significantly.

Periodically-Poled Lithium Tantalate Ridge Waveguides for Efficient Nonlinear Frequency Conversion in the Near UV

Optical damage resistant ridge waveguides for blue and near UV wavelengths have been fabricated using high-temperature Zr and Zn diffusion doping and vapor transport equilibration (VTE) of congruent LiTaO3 crystals. For both dopants high optical damage thresholds >10 MW/cm2 for 532 nm light were demonstrated at room temperature, which can be increased by a factor ~3 when heating the samples to ~150°C. Ridge waveguides with low optical losses of ~0.4 dB/cm were fabricated using diamond-blade dicing. First-order periodic poling with grating periods of ~3 μm can be used for efficient nonlinear frequency conversion for both SHG (800 nm pump) or SPDC (400 nm pump) processes.

Theoretical studies on the local structure and spin Hamiltonian parameters for Cu2+ ions in LiTaO3 crystal.

The local structure and spin Hamiltonian parameters (SHPs) g factors (gx , gy , gz ) and the hyperfine structure constants (Ax , Ay , Az ) for Cu2+ doped in the LiTaO3 crystal are theoretically investigated by the perturbation formulas for a 3d9 ion under rhombically elongated octahedral based on the cluster approach. The impurity Cu2+ was assumed to occupy the host trigonally-distorted octahedral Li+ site and experience the Jahn-Teller (JT) distortion from the host trigonal octahedral [TaO6 ]10- to the impurity rhombically elongated octahedral [CuO6 ]10- . Based on the calculations, the impurity-ligand bond lengths parallel and perpendicular to the C2 -axis are found to be R|| (≈ 2.305 Å) and R⊥ (≈ 2.112 Å) for the studied [CuO6 ]10- cluster, with the planar bond angle θ (≈ 78.2°). Meanwhile, the ground-state wave function for Cu2+ center in LiTaO3 was also obtained. The calculated SHPs based on the above local lattice distortions agree well with the experimental data, and the results are discussed.

Performance of LiTaO3 Crystals and Thin Films and Their Application

Lithium tantalate (LiTaO3, or LT) crystal is widely used in optical applications, infrared detection, and acoustic surface wave devices because of its excellent piezoelectric, pyroelectric, and nonlinear optical properties. In this paper, we discuss the defect structure of LT; the preparation method for LT; the influence of doping on LT; and LT’s application in optical, acoustic, and electrical devices. We mainly analyzed the structure and physical properties of LT crystal, the preparation of LT crystal and LT thin films, the periodic polarization of LT crystal, the reduction of LT wafers, and the application potential of LT crystals in lasers and acoustic surface filters according to the most recent research. We also provide an overview of future research directions for LT in the fields of acoustics, optics, and other fields. The applications of LT in 5G, 6G, SAW filters, nonlinear optical devices, and waveguides are expected to provide additional breakthroughs.

Growth of ferroelectric lithium niobate-tantalate LiNb(1-x)TaxO3 crystals

Congruent and stoichiometric ferroelectric lithium niobate-tantalate crystals LiNb(1-x)TaxO3 of different compositions were grown by the Czochralski method. The stoichiometric crystals were grown using the top seeded solution growth method using LiWO4, which increases the Li content in the melt and in the grown crystal. Also, the use of a solvent can significantly reduce the temperature of the melt. The composition of the crystals was studied by inductively coupled plasma mass spectrometry using laser ablation, which allow studying the change in the composition of the grown crystals along the length and diameter. It is demonstrated that the content of Ta in the crystals exceeds the content of Ta in the initial charge, i.e., in the process of crystal growth, the melt becomes depleted in Ta. It is shown that the Ta content decreases along the crystal length due to the decrease in the Ta content in the melt. In the LiNb0.88Ta0.12O3 crystals, the piezoelectric moduli d22 and d33, and the velocities of bulk and surface acoustic waves were measured. The values of piezoelectric moduli and acoustic wave velocities are shown to occupy an intermediate position between LiNbO3 and LiTaO3 crystals.

Charged domain walls in lithium niobate and lithium tantalate crystals with composition gradients

The formation of charged domain walls (CDWs) in the bulk was studied in lithium tantalate LiTaO3 (LT) and lithium niobate LiNbO3 (LT) crystals with various composition gradients along the polar axis produced by partial vapor transport equilibration (VTE). Under the action of the pyroelectric field upon cooling after the phase transition, the shape of a CDW in LT changed significantly, in contrast to LN: the ledges appeared at CDW and grew toward the polar surfaces. The creation of tail-to-tail and head-to-head CDWs with controlled shape is important for various applications.

Microstructure and hardness evolution induced by annealing of ion irradiated LiTaO3

The evolution of the microstructure and mechanical properties of low-energy heavy-ion-irradiated LiTaO3 crystals annealed at various temperatures was investigated by transmission electron microscopy (TEM) observations and nanoindentation tests to extend the applications of irradiated LiTaO3 crystals. Before annealing, randomly distributed voids formed in an approximately 200 nm thick region at the end of the ion irradiation range, which was attributed to preferential absorption of interstitials by the amorphous-crystalline interface. After annealing, a new directional diffusion path of defects was identified, resulting in a void string. Furthermore, void string diffusion to the free surface was also found during the annealing temperature increase process, which offers a potential application in designing custom sized-thickness exfoliation at the nanoscale. Meanwhile, two competing processes were identified during the annealing process: epitaxial recrystallization from the amorphous-crystalline interface and grain nucleation process in the amorphous region, which formed phases different from the matrix crystal structure, resulting in an interaction between them. Furthermore, the hardness of irradiated samples was also found to be affected by the annealing process; in particular, a hardness decrease induced by the interstitial Fe ions in the recrystallized region was also confirmed, which can improve the processability of samples for further application.

Inductively coupled plasma etching of LiTaO3 in CHF3/Ar plasmas

CHF3/Ar plasma was used to etch LiTaO3 crystal by inductively coupled plasma technology. The etched crystals under different process parameters were analyzed by surface profilometer and characterized by atomic force microscopy and scanning electron microscope. It was shown that ICP power, RIE power, and total gas flow rate had similar effects on etching rate and selectivity, while Ar/(Ar + CHF3) gas ratio had opposite effects on etching rate and selectivity, with better etching rate and selectivity at the ratio of 0.2. Our work gives a fundamental instruction for the fabrication of LiTaO3 based devices.

Structure Formation and Regulation of Au Nanoparticles in LiTaO3 by Ion Beam and Thermal Annealing Techniques.

The size uniformity and spatial dispersion of nanoparticles (NPs) formed by ion implantation must be further improved due to the characteristics of the ion implantation method. Therefore, specific swift heavy ion irradiation and thermal annealing are combined in this work to regulate the size and spatial distributions of embedded Au NPs formed within LiTaO3 crystals. Experimental results show that small NPs migrate to deeper depths induced by 656 MeV Xe35+ ion irradiation. During thermal annealing, the growth of large Au NPs is limited due to the reductions in the number of small Au NPs, and the migrated Au NPs aggregate at deeper depths, resulting in a more uniform size distribution and an increased spatial distribution of Au NPs. The present work presents a novel method to modify the size and spatial distributions of embedded NPs.

Raman Scattering in a Double-Doped Single Crystal LiTaO3:Cr(0.2):Nd(0.45 wt%)

The Raman spectra of a lithium tantalate crystal doubly doped with chromium and neodymium LiTaO3:Cr(0.2):Nd(0.45 wt%) have been studied in this paper. Raman spectra of the first and second orders have been found to be located against the background of a luminescent halo with a maximum at ≈1250 cm−1. Several Raman bands have been detected in the frequency range of 900–2000 cm−1. Their frequencies were 940, 1034, 1113, 1171, 1250, 1343, 1428, 1491, 1582, 1735, 1838, and 1925 cm−1. These bands correspond to overtone processes. We have determined that the frequencies of 1838 and 1925 cm−1 bands are significantly higher than the exact value of the overtone frequency corresponding to the fundamental mode 4A1(z)LO (864 cm−1).

Influence of thermal stress on continuous-wave second-harmonic generation in periodically poled LiTaO3 crystals.

Thermal stress effects on continuous-wave second-harmonic generation in periodically poled LiTaO3 crystals are evaluated via a numerical simulation that is based on nonlinear propagation equations and a thermal conduction equation. The thermal performance and absorption coefficients used in the numerical simulation were determined by comparison with experimental results. The results show that the thermal stress caused by a small residual absorption would restrict the maximum output power of a second-harmonic-continuous-wave laser.

3.4 GHz strip-type thickness shear mode solidly-mounted bulk acoustic wave resonator using X-cut LiTaO3

This paper describes a high-frequency bulk acoustic wave resonator (BAWR) with a solidly-mounted (SM) structure using single crystal LiTaO3 (LT) thin plates. A Bragg reflector solidly supports the LT thin plate, which is fragile if self-suspended. The two kinds of BAWRs use a strip-type thickness shear mode in 0.56 μm thick X37°Y LT and X127°Y LT. The Bragg reflector is made of 5 pairs of Al and Ta films, i.e. 10 layers in total. The X37°Y LT SM structure BAWRs exhibited a resonance frequency (f r) of 3.250 GHz, an anti-resonance frequency (f a) of 3.463 GHz, a bandwidth (BW) of 6.6%, and an impedance (Z) ratio of 48 dB. The X127°Y LT BAWR has a similar characteristic with f r of 3.153 GHz, f a of 3.367 GHz, a BW of 6.8%, and a Z ratio of 46 dB. The X37°Y LT BAWR showed an advantage of 2 dB compared with the X127°Y LT one. The Al film acts as a low acoustic impedance film, but an acoustic impedance layer combination of Al and Ta films is not suitable and that of SiO2 and W films suitable among the four combinations, Al/Ta. SiO2/Ta, Al/W, and SiO2/W films. Although the acoustic impedance layer combination, the acoustic film quality, the structure, electrode design, and fabrication process of the fabricated BAWRs were not optimized yet, this result suggests the high potential of this device.

High-Frequency Vibration Analysis of Piezoelectric Array Sensor under Lateral-Field-Excitation Based on Crystals with 3 m Point Group.

Based on Mindlin’s first-order plate theory, the high-frequency vibrations of piezoelectric bulk acoustic wave array sensors under lateral-field-excitation based on crystals with 3 m point group are analyzed, and the spectral-frequency relationships are solved, based on which, the optimal length–thickness ratio of the piezoelectric crystal plate is determined. Then, the dynamic capacitance diagram is obtained by a forced vibration analysis of the piezoelectric crystal plate. The resonant mode conforming to good energy trapping is further obtained. The frequency interferences between different resonator units are calculated, and the influences of the spacing between two resonant units on the frequency interference with different electrode widths and spacings are analyzed. Finally, the safe spacings between resonator units are obtained. As the electrode spacing value of the left unit increases, the safe spacing d0 between the two resonator units decreases, and the frequency interference curve tends to zero faster. When the electrode spacings of two resonator units are equal, the safe distance is largest, and the frequency interference curve tends to zero slowest. The theoretical results are verified further by finite element method. The analysis model of high frequency vibrations of strongly coupled piezoelectric bulk acoustic array device based on LiTaO3 crystals with 3 m point group proposed in this paper can provide reliable theoretical guidance for size optimization designs of strongly coupled piezoelectric array sensors under lateral-field-excitation.

Multi-color quantum steering frequency comb produced by enhanced Raman scattering

A scheme is proposed to generate multi-color quantum steering frequency comb in a two-dimensional hexagonal-poled LiTaO3 crystal through enhanced Raman scattering. The quantum steering correlations among the Stokes and anti-Stokes Raman beams are demonstrated by applying the criteria for genuine multipartite steering. Multi-color quantum steering frequency comb generated in present scheme has potential application prospects in quantum information processing.

Water contact angles on charged surfaces in aerosols

Interactions between water and solid substrates are of fundamental importance to various processes in nature and industry. Electric control is widely used to modify interfacial water, where the influence of surface charges is inevitable. Here we obtain positively and negatively charged surfaces using LiTaO3 crystals and observe that a large net surface charge up to 0.1 C/m2 can nominally change the contact angles of pure water droplets comparing to the same uncharged surface. However, even a small amount of surface charge can efficiently increase the water contact angle in the presence of aerosols. Our results indicate that such surface charges can hardly affect the structure of interfacial water molecular layers and the morphology of the macroscopic droplet, while adsorption of a small amount of organic contaminants from aerosols with the help of Coulomb attraction can notably decrease the wettability of solid surface. Our results not only provide a fundamental understanding of the interactions between charged surfaces and water, but also help to develop new techniques on electric control of wettability and microfluidics in real aerosol environments.

Robust single-frequency 589 nm fiber laser based on phase modulation and passive demodulation.

A robust 20-W continuous-wave single frequency 589 nm laser is developed to aim for sodium guide star in astronomy. The source is based on applying π-depth binary phase modulation to a single frequency seed laser along with 3 steps of strain in the gain fiber to suppress the stimulated Brillouin scattering in the high power 1178 nm amplifier and realizing the recovery of single frequency after frequency doubling in a periodically poled LiTaO3 crystal. The efficiency of frequency doubling reaches up to 41.6%. To the best of our knowledge, it is the highest power reported for continuous-wave 589 nm laser generation by single-pass frequency doubling. The approach significantly simplifies the sodium guide star laser design and improves robustness.