Growth and optical properties of Mg, Fe Co-doped LiTaO3 crystal

Mg, Fe double-doped LiTaO₃ and LiNbO₃ crystals have been grown by Czochralski method. The optical properties were measured by two-beam coupling experiments and transmitted facula distortion method. The results showed that the photorefractive response speed of Mg:Fe:LiTaO₃ was about three times faster than that of Fe:LiTaO₃, whereas the photo-damage resistance was two orders of magnitude higher than that of Fe:LiTaO₃. In this paper, site occupation mechanism of impurities was also discussed to explain the high photo-damage resistance and fast response speed in Mg:Fe:LiTaO₃ crystal.     

Nonvolatile holographic recording in Ti, Fe Co-doped LiTaO3 crystal

Ti, Fe Co-doped LiTaO₃ (LT) crystals have been grown by the Czochralski method from the congruent melts. The absorption spectra of crystal were measured before and after ultraviolet illumination. Holograms have been recorded in doubly doped crystals with continuous-wave laser light by use of two-color method. The maximum value of refractive-index changes 7×10⁻⁵ is achieved.     

基于周期极化LiTaO3晶体的高增益简并啁啾脉冲参量放大

根据准相位匹配理论计算了周期极化LiTaO₃(PPLT)晶体中0类准相位匹配过程(e+e→e)的增益曲线.在此基础上，使用数百μJ的低抽运能量获得了～10⁶的增益和～10.3%的转换效率，实现了中心波长位于1064nm的基于简并光学啁啾脉冲参量放大(OPCPA)技术的高增益放大，为产生超短超强激光脉冲提供了新的技术手段.实验结果与理论预期基本符合.     

Degenarate four-wave mixing in LiNbO3 and LiTaO3

Continuous wave generation of complex conjugate wavefront via four-wave mixing in LiNbO₃ and LiTaO₃ with diffusion non-linearity is studied. Strong anisotropy of the degenarate four-wave mixing is observed and explained.     

Soft vibrational mode in LiNbO3 and LiTaO3

The temperature dependence of the far-infrared reflectivity as obtained with a scanning interferometer for the A₁- and E-type modes of both LiNbO₃ and LiTaO₃ is reported in the ferroelectric phase. Results of a Kramers-Kronig analysis are compared with Raman and neutron scattering data which are controversial about the existence of a soft vibrational mode. For LiTaO₃, spectra are obtained 300 K above the Curie temperature, in the paraelectric phase. The lowest-frequency A₁ (TO) mode is unambiguously found as soft and becomes rapidly overdamped.     

Resonant Raman scattering in single crystal of congruent LiTaO3 : Effect of excitation energy

Large dispersion in the peak position of the OH⁻ stretching mode (∼687.9 and ∼2167.7 cm⁻¹/eV for fundamental and 3rd harmonic, respectively) is observed by Resonance Raman studies in congruent lithium tantalate single crystal under varying excitation energies. This is explained by considering the involvement of multiple LO phonons in the interaction with OH⁻ stretching vibration and the resonantly excited electrons. The intensity of the peaks is also found to vary with the excitation energy. FWHM increases with the increase in excitation energy because of individual contributions of the increasing number of resonance steps to the broadening.     

Y3Al5O12:Ce3+ fluorescent ceramic for optical data storage

A kind of optical data storage medium based on electron-trapping materials,Y₃Al₅O₁₂:Ce³⁺fluorescent ceramic,was developed by vacuum sintering technology.The medium shows sufficiently deep traps[1.67 and 0.77 eV).The properties of trap levels were researched by thermoluminescence curves,and the optical storage mechanism based on Ce³⁺ion doping was proposed.More importantly,the data can be written-in by 254 nm UV light,and readout by heating[3...     

Crystal growth and spectroscopic characterization of Yb:LiTaO3

Spectroscopic properties are presented for Yb³⁺ incorporated into single crystals of LiTaO₃ grown by the top-seeded solution growth method. From an analysis of the absorption and fluorescence spectra, we are able to determine the Stark-level components of the ²F_7/2 (the ground-state multiplet manifold) and the ²F_5/2 (the excited-state multiplet manifold of Yb³⁺ (4f¹³)). The room-temperature fluorescence lifetime of ²F_5/2 is 678 μs as measured on a thin sample to reduce possibilities for reabsorption. Spectral comparisons of Yb³⁺-doped LiTaO₃ and LiNbO₃ are drawn. The crystal-field splitting of Yb³⁺(4f¹³) in both crystal hosts is modeled using a set of crystal-field splitting parameters, B_nm, determined from a recent spectroscopic analysis of Er³⁺(4f¹¹) in LiNbO₃. Without adjustment of the B_nm parameters, the model predicts the Stark-level energy and the symmetry label for each level in reasonable agreement with the experimental values. Less photorefractive than its niobate cousin, LiTaO₃ has potential for use in numerous integrated electro-optical circuits and devices.     

Theoretical explanation of g factors for Ti ions in LiNbO3 and LiTaO3 crystals

The EPR g factors g_// and g_⊥ for Ti³⁺ ions at the trigonal octahedral Li⁺ sites of LiNbO₃ and LiTaO₃ crystals are calculated from the third-order perturbation formulas of g factors for 3d¹ ion in trigonal symmetry. In the calculations, the crystal-field parameters are obtained from the structural data by using the superposition model. The calculated values are in reasonable agreement with the observed values. The results are discussed.     

Picosecond study of color center translocation in LiTaO3

By the use of dual-beam picosecond absorption spectroscopy technique, we observed color center dislocation in LiTaO₃ single crystal. The time constant for the translocation was found to be 100 ± 40 psec, and independent of excitation laser power.     

Anomalous polariton dispersion in LiTaO3 near Tc

Anomalous leveling of the A₁(Z) polaritons of ferroelectric LiTaO₃ was observed below certain wavevectors on approaching the Curie temperature. The saturation is attributed to the destruction of the polaritons propagation length due to the crystal domain variations, which is interpreted as a new phase transition model. The almost linear dependence of the propagation length does indicate the Curie temperature to be 873 K.     

Subnanosecond multiphonon relaxation of divalent copper impurities in LiTaO3

The temperature dependence of the lifetime of the excited ²T₂ state of the Cu²⁺ ion in a LiTaO₃ crystalline host has been measured with picosecond optical pulses. Its value ranges from 450 psec at 22°K to 10 psec at 423°K. Consistent with this result is the observation of weak fluorescence at 1.75 μm having a low temperature quantum efficiency of ～ 10^?6. The experimental results are in reasonably good agreement with recent theoretical models based on strong coupling of the Cu²⁺ impurities to the host lattice.     

Fringe-variable interferometry used for the detection of domain structure in LiTaO3

We design a fringe-variable Jamin interferometer to detect the reversed domain of a ferroelectric crystal in real time. In contrast to the Mach-Zehnder interferometer, this setup is compact and tunable in fringe frequency. In experiments, we use it to detect the partly reversed domains of Stoichiometric LiTaO₃ (SLT). Selecting the proper fringe cycle, we can estimate the average phase shift between the original and reversed domains through eyeballing. Furthermore, in the interferogram processing, we use the FFT methods to reconstruct the phase according to the original fringe and deformed fringe, and obtain the phase variance at the domain wall. The results show that the average phase variance at the domain wall is in good agreement with the theoretical value.     

Compensation for time dependent phase inhomogeneity via degenerate four-wave mixing in LiTaO3

Compensation for static (aberrating glass plate) and dynamic (crystal with optical damage) phase distortion via complex conjugate wavefront generation in four-wave mixing in LiTaO₃ crystals with specific diffusion nonlinearity is demonstrated.     

Investigation of nonvolatile holographic storage in LiNbO3:Mn:Ce:Fe crystal

We investigate the persistent holographic recording in triply doped LiNbO₃:Mn:Ce:Fe crystals at different oxidation/reduction states. The experimental results show that there is an optimum oxidation/reduction state, which results in the best dynamic range M/#. Compared with doubly doped LiNbO₃:Ce:Fe, we found that the nonvolatile diffraction efficiency and the best dynamic range M/# obtained in triply doped samples are larger than that obtained in doubly doped samples. The reason for the increase of the crystal about the nonvolatile diffraction efficiency and the dynamic range M/# was also explained.     

钽酸锂铁电相变的喇曼光谱研究

本文测定了钽酸锂晶体从室温到居里温度以上(20—800℃)的喇曼光谱。没有观察到软模现象。我们发现在居里点附近,铁电相和顺电相的喇曼光谱十分一致,经过居里点喇曼光谱不发生变化。根据这个新的实验结果和文献上关于用中子衍射测定的晶体结构资料,我们做出了钽酸锂的铁电相变为有序无序型的推论。 关键词：     

Improved nonvolatile holographic storage sensitivity of near-stoichiometric LiNbO3:Fe:Mn crystals

We investigate the nonvolatile holographic storage characteristics of near-stoichiometric LiNbO3 :Fe:Mn crystals with different Li2O contents. Experimental results indicate that the optimal value of Li2O content is about 49.6 mol%. Nonvolatile sensitivity S considerably improved to 0.15 cm/J because of the use of near-stoichiometric LiNbO3 :Fe:Mn with 49.6 mol% Li2O.     

Experimental study of Love-wave immunosensors based on ZnO/LiTaO3 structures

Experimental study of Love-mode immunosensors based on structures of ZnO/36°YX-LiTaO₃ is presented, in which the ZnO films with c-axis (0 0 2) orientation have been successfully grown on the 36°YX-LiTaO₃ substrates by RF magnetron sputtering technique. Then the Love-mode immunosensors based on the ZnO/36°YX-LiTaO₃ structures and monitoring antibody-antigen immunoreactions in aqueous solutions in real time are fabricated. The experimental results show that the optimal thickness of ZnO layers is about 1.20 μm in the structures deposited on 36°YX-LiTaO₃ substrates, which is much less than that of SiO₂ overlayers about 6 μm. The antibody-antigen immunoreaction experiments also show that the frequency shifts of the sensors with 1.33 μm ZnO films are proportional to the concentration of antigen in solution as the concentration range less than 100 μg/ml.     

LiNbO3和LiTaO3单晶体中亚晶界位错结构的研究

本文应用透射法和超显微法对用金缀饰后的LiNbO₃和LiTaO₃单晶体进行了直接观测,观察到两种晶体中亚晶界的三维面貌,对亚晶界进行了极图分析,并进一步用Frank公式进行了定量验证。通过对位错网及三叉亚晶界的分析,表明该类晶体中存在的位错的Burgers矢量是:最短点阵平移矢量——六角晶胞的基矢<1210>,次短点阵平移矢量——菱胞基矢1/3<0111>,以及再次短点阵平移矢量——菱胞短体对角线分1/3<2021>。 关键词：     

Optical spectrum, local lattice structure and EPR g factors for Cr impurity ions in MgTiO3 and LiTaO3

On the basis of the 120×120 complete energy matrices for a d³ configuration ion in a trigonal ligand field, for Cr³⁺ ions doped in MgTiO₃ and LiTaO₃, the local structures and EPR g factors of the octahedral (CrO₆)⁹⁻ clusters have been studied, respectively. By simulating the calculated optical spectra and the EPR spectra data to the experimental results, local structure parameters are obtained. The calculated results show that although the local lattice structures around the M (M=Mg²⁺, Ta⁵⁺) ions are obviously different, after Cr³⁺ replacing the M, the local lattice structures around the Cr³⁺ ions are quite similar and close to those of the Cr₂O₃. This may be ascribed to the fact that the octahedral Cr³⁺ center in MgTiO₃:Cr³⁺ and LiTaO₃:Cr³⁺ systems and that in Cr₂O₃ exhibit similar octahedral (CrO₆)⁹⁻ clusters. Moreover, the corresponding theoretical values of the optical spectra have been reported. It is also found that the orbital reduction factor k is very important to understand the EPR g factors for Cr³⁺ ions doped in MgTiO₃ and LiTaO₃.