Influence of surroundings on photorefractive effect in lithium niobate crystals

In the paper results of the investigation of the influence of electric properties of the environment surrounding LiNbO₃ crystals on photorefractive effect induced in these crystals by Gaussian Ar⁺ laser beam with various intensities are presented. We show spatial and temporal dependences of changes of the refractive index obtained experimentally in LiNbO₃: Fe and LiNbO₃: Fe:Mn samples surrounded by media with different electric conductivities and different permittivities (water, air, water solution of CaCl₂). The space and time dependences of the refractive index changes induced by the Ar⁺ laser beam are observed by means of the Mach–Zehnder interferometer using light from HeNe laser. The experimentally obtained results are in a good agreement with those following from numerical calculations using the manifold mirroring method. The agreement between calculated and experimental results indicates that the polarization charge at the photorefractive crystal/surrounding medium boundary significantly influences the photorefractive process in the crystal. The experimentally observed slow spontaneous decrease of the refractive index change in a sample placed into a slightly conducting medium (air) after switching off the beam also indicates that the polarization charge in the sample's surroundings affects the photorefraction.     

Optofluidic droplet router

This contribution presents an optofluidic droplet router which is able to route and steer microdroplets using optically induced forces created solely by the bulk photovoltaic effect on a nonlinear substrate. The combination of microfluidic tools with the properties of a photorefractive crystal allows for the generation of dielectrophoretic forces that can be either repulsive, leading to virtual barriers, or attractive, creating virtual rails. The sign of these forces is solely determined by the electrical properties of the liquid medium under investigation. Moreover, the induced structures on the bottom of the microfluidic channel are optically reconfigurable, so that the same device can easily be adopted for different purposes. Appropriate droplet‐generating devices are fabricated by UV illumination of SU‐8 and polydimethylsiloxane replica molding of the master structures. The bottom of the channels is formed by an iron‐doped lithium niobate crystal, whose internal electric fields are induced by structured illumination patterns and exert dielectrophoretic forces on droplets in the microfluidic section.

     

一种通过梯形PPMgLN波导倍频实现带宽可调谐光源的理论研究

本文设计了一种梯形的周期极化掺镁铌酸锂(PPMgLN)波导,并通过在传播方向上引入温度梯度来拓宽其倍频(SHG)过程的泵浦光源可接收带宽。通过有限差分的光束传输法,计算波导的有效折射率,并进行波导尺寸的设计。结果表明,通过改变梯形波导不同位置的温度,使其形成一个温度梯度,可拓宽泵浦光源的波长可接收带宽。本文所设计的PPMgLN波导最大泵浦光源可接收带宽为C波段,即1 530~1 565 nm,该波导可倍频C波段,得到输出波段带宽为765~782.5 nm,温度调谐范围为30~150 ℃。     

Yb3+掺杂稀土钽铌酸盐的晶体场从头计算研究

Yb³⁺掺杂晶体材料是重要的激光材料,在超短脉冲激光、大功率激光等领域有重要应用前景,但长期以来很难通过实验拟合确定Yb3+晶体场参数,尤其是低对称体系,从头计算是解决此问题的重要途经.本文介绍了适合计算稀土离子掺杂晶体的从头计算DV-Xα方法和有效哈密顿量模型,用该方法计算了Yb³⁺掺杂M型和M'型钽铌酸盐的晶场参数和旋轨耦合参数,得到的能级结构和实验能很好地符合,并发现了Yb³⁺掺杂钽铌酸盐的晶场强度参数随稀土原子序数呈现规律变化.表明结合DV-Xα计算和有效哈密顿量方法是计算Yb³⁺掺杂低对称钽铌酸盐晶体场的有效途径,结果显示Yb3+掺杂钽铌酸盐晶体有望成为新型全固态激光工作物质.     

铜铁镁三掺铌酸锂晶体的第一性原理研究

利用基于密度泛函理论的第一性原理,研究了Cu:Fe:Mg:LiNbO3晶体及对比组的电子结构和光学特性.研究显示,单掺铜或铁铌酸锂晶体的杂质能级分别由Cu 3d轨道或Fe 3d轨道贡献,禁带宽度分别为3.45和3.42 eV;铜、铁共掺铌酸锂晶体杂质能级由Cu和Fe的3d轨道共同贡献,禁带宽度为3.24 eV,吸收峰分别在3.01,2.53和1.36 eV处;Cu:Fe:Mg:LiNbO3晶体中Mg^2+浓度低于阈值或高于阈值(阈值约为6.0 mol%)的禁带宽度分别为2.89 eV或3.30 eV,吸收峰分别位于2.45 eV,1.89 eV或2.89 eV,2.59 eV,2.24 eV.Mg^2+浓度高于阈值,会使吸收边较低于阈值情况红移;并使得部分Fe^3+占Nb位,引起晶体场改变,从而改变吸收峰位置和强度.双光存储应用中可选取2.9 eV作为擦除光,2.5 eV作为读取和写入光,选取Mg^2+浓度达到阈值的三掺晶体在增加动态范围和灵敏度等参量以及优化再现图像的质量等方面更具优势.     

胍盐化合物[C(NH_2)_3]_(6.3)K[Nb_(1.3)W_(10.7)O_(40)H_2]·H_2O的合成及性质

通过粉状白钨酸和可溶性铌酸钾水溶液的反应,合成了十二聚系列的钨铌杂多阴离子胍盐化合物[C(NH_2)_3]_(6.3)K[Nb_(1.3)W_(10.7)O_(40)H_2]·H_2O,研究了其水溶液的酸碱稳定性。根据红外、拉曼和紫外光谱、化学性质,认为该化合物可能具有十二聚偏钨酸根阴离子的结构骨架。     

新铌酸盐Ba5NdTi3Nb7O30的合成与介电性能

The New Niobate Ba₅NdTi₃Nb₇O₃₀ was synthesized by solid state reaction at 1250℃ for 48h. The crystal structure and dielectric properties of Ba₅NdTi₃Nb₇O₃₀ were determined by X-ray powder diffraction and dielectric measurements. The results show that Ba₅NdTi₃Nb₇O₃₀ belongs to ferroelectric phase of tetragonal tungsten bronze structure at room temperature with unit cell parameters: a=1.24424(4)nm, c=0.39476(2)nm, calculated density 5.719g·cm^-3. Ba₅NdTi₃Nb₇O₃₀ belongs to relaxor ferroelectrics. The phase transition temperature (T_c) of Ba₅NdTi₃Nb₇O₃₀ from ferroelectric to paraelectric is found to shift toward higher temperature side at higher fre-quency, and T_c is 90℃ at 1kHz. At room temperature, the dielectric constant (ε_r) and dielectric loss of Ba₅NdTi₃Nb₇O₃₀ decrease with the increase of frequency, and Ba₅NdTi₃Nb₇O₃₀ ceramic have high dielectric constant 489 at 1kHz.     

Synthesis of Ultra-Fine Columbite Powder MgNb2O6 by the Polymerized Complex Method

Pure MgNb₂O₆ powders with high specific surface area and high crystallinity have been successfully synthesized by the Polymerized Complex (PC) Method. A solution of water, citric acid, ethylene glycol and niobium and magnesium ions, was polymerized at 130°C by the water elimination and was calcined at 400°C for 2 h. The precursor formed was calcined at temperatures from 700°C to 1000°C in air to obtain the columbite phase. Thermal analysis, Raman spectroscopy, x-ray diffraction, adsorption/desorption hysteresis and scanning electron microscopy were used to investigate the polymer decomposition and the columbite phase evolution. No evidence for phase separation of crystalline MgCO₃ and Nb₂O₅ in Raman spectra and x-ray diffraction pattern as distinct intermediates were found, and the MgNb₂O₆ probably is formed through a single-step decomposition of oxycarbonate intermediate, as other double oxide synthesized by the PC Method, as indicated by the thermal decomposition of the precursor.     

Investigation of thermal evolution of nanodomain structures in nonlinear barium sodium niobate crystals

By the 90°elastic light scattering investigation and far field observation in the range of 20-800℃,the relation between behavior of light scattering anomalies and evolution of nanodomain structures in lattice of barium sodium niobate(Ba2NaNb5O15,BSN)crystal was clarified.The correlation between anomalies on the temperature curves of the elastic light scattering intensity and temperature transformations of nanodomains was studied by X-ray and electron microscope methods.Phase transition near 500℃ and movement in field of scattering light could be explained by appearance of a new incommensurate phase.     

A periodically poled LiNbO3 optical parametric generator in wavelength conversion from 2 to 3.88-4.34 μm

A periodically poled lithium niobate (PPLN) optical parametric generator (OPG) pumped by a laser diode (LD)-pumped Q-switched Tm,Ho:GdVO4 laser operated at 2.048 μm with pump pulse of 25 ns and repetition rate of 10 kHz is reported.