LiTaO3 Crystal Research Articles

Study of optical elastic scattering in a quasiperiodically poled LiTaO3 crystal

In this letter we report the experimental result on the study of light scattering in a one-dimensional quasiperiodically poled LiTaO3 crystal. The infrared scattering signal in the crystal was upconverted into visible band by sum frequency with incident light, forming a set of coaxial conical second harmonic beam with a quasiperiodic ratio at the radius. The quasi-phase-matching significantly enhanced such a nonlinear interaction. The angular distribution of scattering light in crystal was extracted from the experimental result. This reveals a possible application of quasiperiodic structure on the study of light scattering.

Characterization of zinc-modified lithium tantalate thin films fabricated by chemical solution deposition method

Zinc-substituted lithium tantalate thin films were fabricated for improving the electrical resistivity by compensating the valence of lattice defects in LiTaO3 crystal. The films with the chemical composition of (Li1.00-xZnx)TaO3 were fabricated on (111)Pt/TiO2/SiO2/(100)Si substrate by a chemical solution deposition technique using metal-organic precursors. Dense films consisting of a ilumenite-type crystalline phase were deposited by spin coating on the substrates, followed by heat-treatment at 650°C for 5 min in air. The leakage current density of the LiTaO3 film was reduced from approximately 10−4 to 10−6 A/cm2 by substituting Zn2+ ions for Li+ ions in the LiTaO3 films. Polarization–electric field hysteresis loop was improved significantly by partial substitution of Zn2+ for Li+ ions, which is based on the enhancement of electrical resistivity.

EPR Theoretical Study of the Local Lattice Structure of Fe3+ Doped in MgTiO3 and LiTaO3

The EPR zero-field splittings of Fe3+ doped in MgTiO3 and LiTaO3 are studied by diagonalizing the complete energy matrices of the electron-electron repulsion, ligand-field and spin-orbit coupling interactions for a d5 configuration ion in a trigonal ligand-field. It is shown that, when Fe3+ is doped in aMgTiO3 or LiTaO3 crystal, the local lattice structure around the octahedral Fe3+ center has an obvious distortion along the C3 axis. By simulating the second- and fourth-order EPR parameters D and (a−F) simultaneously, the local structure parameters of Fe3+ doped inMgTiO3 and LiTaO3 crystals are determined, which reveal that Fe3+ occupies both the Mg2+ and Ti4+ sites in the MgTiO3:Fe3+ system and occupies the Li+ site rather than the Ta5+ site in the LiTaO3:Fe3+ system. The results accord with the ENDOR and EPR experiments. - PACS numbers: 71.70.Gm; 75.30.Et; 71.70.Ch.

High-power, blue-light generation in a dual-structure, periodically poled, stoichiometric LiTaO3 crystal

High-power blue light was generated from a diode-side-pumped Q-switched 1319 nm Nd:YAG laser with a periodically poled, stoichiometric LiTaO3 (PPSLT) crystal. The PPSLT sample used in this experiment consists of two segments in series: the first segment has a period of 14.08 μm for the second harmonic generation (SHG) and the second segment has periods of around 4.6 μm for the generation of blue light by mixing fundamental and SH. An average power of 466 mW of a 440 nm blue light was obtained at the fundamental power of ∼5.4 W with a conversion efficiency of 8.6%. The output power fluctuated by 3% over a half-hour period. This result indicates that our scheme is a practical method to construct a reliable compact blue laser.

High-gain degenerated optical parametric chirped-pulse amplification in periodically poled LiTaO3

The gain curve in periodically poled LiTaO3 crystal (PPLT) was calculated for type 0 (e+e→e) quasi-phase matching (QPM). A high-gain amplifier centered at 1064nm based on degenerated optical parametric chirped-pulse amplification was built. The gain of ～106 and ～10.3% conversion efficiency were achieved with low pump energy of several hundreds of μJ. The experimental results are consistent with the simulation.

Monolithic red-green-blue laser light source based on cascaded wavelength conversion in periodically poled stoichiometric lithium tantalate

A compact, pulsed, red, green, and blue laser source based on cascaded quasi-phase-matched wavelength conversion in two periodic superlattices set in tandem in a single stoichiometric LiTaO3 crystal and pumped by a laser source at 532nm is reported. The white light equivalent flux obtained was 80lmper1W input with a green to white light power conversion efficiency of >30%. Unity power conversion is feasible in this monolithic approach.

Fabrication of polaritonic structures in LiNbO3 and LiTaO3 using femtosecond laser machining

Fabrication of patterned materials in ferroelectric LiNbO3 and LiTaO3 crystals using femtosecond laser micromachining is presented and discussed. Damage feature sizes in the 10–100 μm range were achieved using 800-nm, 50-fs (FWHM) ultra-fast laser pulses with energies ranging from 10 μJ up to 350 μJ. Fabrication of polaritonic devices such as waveguides, resonators, focusing reflectors, diffractive and dispersive elements, photonic band gap materials, and other microstructures is demonstrated.

Thermal stability of LiTaO3 domains engineered by scanning force microscopy

The stability of domains engineered in near-stoichiometric and congruent composition LiTaO3 crystals was investigated after heat treatment using scanning force microscopy. Piezoresponse images of the domains showed that the heat treatment had induced backswitching in the near-stoichiometric crystals and that the degree of backswitching depended on the domain structure and heating temperature. No backswitching was observed in the congruent composition crystals after the same heat treatment. The thermal stability of engineered LiTaO3 domains thus depends on the number of nonstoichiometric defects, the domain wall energy, and the pyroelectric effect.

Growth and studies of optical properties of double‐doped In:Fe:LiTaO3 crystal

AbstractIn:Fe:LiTaO3 crystals were grown in an air atmosphere using the Czochralski method. The photorefractive properties were measured by the two‐wave coupling experiments, and light‐induced scattering was used to characterize the optical damage. It was found that the photorefractive response speed of In:Fe:LiTaO3 was about four times faster than that of Fe:LiTaO3, and the resistance ability to optical damage was drastically improved. The increase in damage resistance and faster response speed could be attributed to the Fe3+ losing their electron acceptor properties and, therefore, an increase in photoconductivity. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2227–2230, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21919

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.

Wavelength dependence of electronic and ionic contributions re and ri in an LiTaO3 crystal

The values and wavelength dependence of the electronic and ionic contributions, re and ri, to the clamped electro-optic (EO) coefficients r22 and rc in a LiTaO3 crystal have been determined and are given over a wavelength range from 0.514 up to 1.321 µm. This work has been realized on the basis of measurements of the clamped EO coefficients, using a series of laser sources, combined with recorded data on the second-harmonic generation coefficients. The above results are discussed and compared with those obtained for a LiNbO3 crystal.

Thermo-optic effects in electro-optic crystals used in an intensity-modulation system. – Application in LiTaO3

Linear electro-optic (EO) and thermo-optic (TO) effects are jointly considered on the basis of field-induced and temperature-affected perturbations of the operating point along the optical transmission curve of an EO-modulation system. In this framework, methods of EO measurements based on the frequency doubling appearing at the minimum-transmission point are formulated. Moreover, TO coefficients for various optical quantities, such as the refractive indices, n0 and ne, the spontaneous birefringence Δn(0), the EO coefficient r, the half-wave voltage Vπ, the optical phase retardation Γ, and the intensity modulation (IM) depth, m, are introduced and useful relationships between them are extracted. Also, applications of the above in the experimental field, with determinations of EO parameters and TO coefficients, are presented for the case of a congruent LiTaO3 crystal. A comparison of the so-obtained experimental results with those derived from literature when a LiNbO3 crystal is used demonstrates a number of advantages for the LiTaO3-based system.

Parametric amplification of few-cycle carrier-envelope phase-stable pulses at 21 μm

We demonstrate an optical parametric chirped-pulse amplifier producing infrared 20 fs (3-optical-cycle) pulses with a stable carrier-envelope phase. The amplifier is seeded with self-phase-stabilized pulses obtained by optical rectification of the output of an ultrabroadband Ti:sapphire oscillator. Energies of -80 microJ with a well-suppressed background of parametric superfluorescence and up to 400 microJ with a superfluorescence background are obtained from a two-stage parametric amplifier based on periodically poled LiNbO3 and LiTaO3 crystals. The parametric amplifier is pumped by an optically synchronized 1 kHz, 30 ps, 1053 nm Nd:YLF amplifier seeded by the same Ti:sapphire oscillator.

Characterization of periodically poled LiTaO3 crystals by means of spontaneous parametric down-conversion

We describe the observation of quasi-phase-matched spontaneous parametric down-conversion in eee-geometry in periodically poled LiTaO3 crystals. For scattered light, the two-dimensional angular-frequency intensity distribution was studied. Several detuning curves were recorded, corresponding to high orders m=-2, -3, -4, -5 of quasi-phase matching. The measured periods of domain gratings agree with the data obtained by atomic-force microscopy for the etched crystal surfaces. The presence of both odd and even orders indicates that the lengths of positive and negative domains are unequal. To determine the mean duty cycle for regular domain gratings we propose comparing of the intensities of spontaneous parametric down-conversion in different orders of quasi-phase-matching.

Measurements of ion‐induced ferroelectric emission and surface charge dynamics on LiTaO3(0001) by time‐of‐flight scattering and recoiling spectrometry (TOF‐SARS)

AbstractWe have derived a special surface analysis method for studying surface charge dynamics on ferroelectrics from time‐of‐flight ion scattering and recoiling spectrometry (TOF‐SARS). In this method, shifts of the TOF‐SARS peaks of a ferroelectric crystal are measured as a function of sample temperature, and these spectral data are used to deduce changes in electrical potential on the sample surface. These changes are then converted to information on surface charge dynamics. In addition, the method is also applicable in extracting data regarding ion‐induced ferroelectric electron emission (FEE) from the TOF‐SARS spectra. In this work, we have tested the method with LiTaO3(0001) crystals having the nominal stoichiometry and single domain properties. Our results show that for temperature changes from 25 to ∼100 °C, the excess amount of surface charge induced by pyroelectricity, ion irradiation, and ion‐induced electron emission is drained mainly by surface conductivity. For temperature changes above 100 °C, the bulk ionic conductivity becomes an important charge drainage channel. Our measurements give an activation energy of 0.75 eV for the thermally activated ionic conductivity, and the result agrees well with the literature value previously obtained by d.c. conductivity measurements. Copyright © 2006 John Wiley & Sons, Ltd.

Study on Chemical Mechanical Polishing Mechanism of LiTaO<sub>3</sub> Wafer

In this paper, the scratching processes by a diamond indentor under the loads linearly increased from zero were studied to assess the mechanical behavior of LiTaO3 crystal wafer. Material removal mechanism of LiTaO3 crystal by mechanical loads was analyzed based on the measured acoustic signals in the scratching processes and the observation on the scratched surfaces of LiTaO3 wafers. The chemical mechanical polishing (CMP) processes of LiTaO3 wafers were analyzed in detail according to the observation and measurement of the polished surfaces of LiTaO3 wafers with SEM and XRD. The research results show that there exist four regimes along the scratched groove with the increasing of down force in a scratching process of LiTaO3 crystal wafer, and the critical load for each regime is affected by the loading speed and final load, etc. When H2O2 and KOH are added into the polishing slurry, the material of LiTaO3 wafer is removed by chemical reaction and mechanical action sequentially in the CMP processes, and the material removal rate increases while the surface roughness is improved.

Thermal inhibition of high-power second-harmonic generation in periodically poled LiNbO3 and LiTaO3 crystals

A coupled thermo-optical model shows strong thermal inhibition of second-harmonic generation (SHG) in periodically poled (PP) LiNbO3 (PPLN) and stoichiometric LiTaO3 (PPSLT) crystals. Three-dimensional simulations performed for a 1.064μm fundamental wavelength pulsed nanosecond laser beam 150μm in radius show the onset of significant temperature nonuniformities along and across the irradiated zone, and strong thermal dephasing and inhibition of SHG in these crystals for input powers >10W. PPSLT is found to have a significant advantage over PPLN due to the higher heat conductance, decreasing these temperature nonuniformities and allowing one to maintain the irradiated zone within the corresponding SHG temperature tolerance range (ΔT≈3K).

SPM IMAGING OF DOMAINS IN PERIODICALLY POLED LiTaO3 CRYSTALS

ABSTRACT Periodically poled LiTaO3 crystals without erosion were characterized by a scanning probe microscope (SPM) using the converse piezoelectric effect. The on-tip force which was controlled by the setpoint value had significant effect on the characterization of domains and domain walls. The piezoresponse (PR) phase and PR amplitude varied with the change of the setpoint value. When the setpoint value was 0 V, the phase difference between neighboring 180° domains reached 180°. The width of domain walls calculated from the PR phase reached the minimum value while that calculated from the PR amplitude reached the maximum at the setpoint value of 0 V. The above minimal and maximal width approached each other at about 400 nm. These phenomena indicate that selecting a moderate on-tip force is very important for the piezoresponse force mode (PFM). PFM can be used to characterize the domain walls that s different from the inner of the domains in physical properties such as piezoelectricity.

Investigation of Three-Dimensional Domain Structure in LiTaO3 by Scanning Nonlinear Dielectric Microscopy

The three-dimensional domain configuration of multidomain LiTaO3 is revealed by scanning nonlinear dielectric microscopy (SNDM). SNDM can measure the polarization components both perpendicular and parallel to the surface of a specimen. These techniques are applied to both congruent and stoichiometric LiTaO3 crystals. The images obtained by SNDM measurements allow us to confirm the various domain features of LiTaO3 and to understand both similarities and differences between congruent and stoichiometric compositions.

Dielectric and Pyroelectric Properties of 〈111〉‐Oriented Fe‐Doped 0.62Pb(Mg1/3Nb2/3)O3–0.38PbTiO3 Single Crystals

Fe‐doped 0.62Pb(Mg1/3Nb2/3)O3–0.38PbTiO3 (PMN–0.38PT) single crystals were grown by a modified Bridgman technique. Two kinds of single crystals with different iron ion molar ratios, (i) 0.2 mol% and (ii) 1.0 mol%, were obtained. The effect of doping iron ions on the dielectric and pyroelectric properties of the 〈111〉‐oriented PMN–0.38PT single crystals was examined. The temperature of the permittivity maximum (Tm) exhibits no dispersion behavior and decreases with increasing doping concentration. The dielectric loss of the 0.2 mol% Fe‐doped PMN–0.38PT single crystal is much lower than that of the high dopant content crystal (1.0 mol%) and undoped crystal, which makes it possess excellent pyroelectric performance. By a dynamic method, the measured pyroelectric coefficient and detectivity figure of merit (FD) of 0.2 mol% Fe‐doped PMN–0.38PT single crystal are 439 μC/m2·K and 56.3 μPa−1/2, respectively, both better than those of widely used pyroelectric single crystal LiTaO3. The results imply that the single crystal is a promising candidate for infrared detectors and other pyroelectric applications. The mechanism of doping effect was also discussed based on the principles of crystal chemistry.