光折变晶体钛酸钡锶电荷传输参数的测量

报道用两波耦合技术测量光折变晶体钛酸钡锶(Ba_(1-x)Sr_xTiO-3,BST)的电荷传输参数φμτ在激光波长λ=515nm和光功率密度I—1W/cm~2下测得光折变响应时间为0.5sec.考虑到BST晶体吸收系数的光强相关性,修改了光栅形成率的函数变量,得到BST晶体的暗电导σ_a和电荷传输参数φμτ的拟合值分别为1.0×10~(-11)(Ωcm)~(-1)和2.8×10~(-10)cm~2/V.     

用耦合波方法研究取样光栅的衍射特性

 介绍了利用耦合波理论编写计算光栅衍射特性程序的基本思想和主要步骤。利用编写的程序计算并分析了一种用于激光取样光栅TE波和TM波的衍射特性。     

Asymmetric dynamic phase holographic grating in nematic liquid crystal

A new scheme for recording a dynamic phase grating with an asymmetric profile in C60-doped homeotropically aligned nematic liquid crystal(NLC) was presented.An oblique incidence beam was used to record the thin asymmetric dynamic phase holographic grating.The diffraction efficiency we achieved is more than 40%,exceeding the theoretical limit for symmetric profile gratings.Both facts can be explained by assuming that a grating with an asymmetric saw-tooth profile is formed in the NLC.Finally,physical mechanism and mathematical model for characterizing the asymmetric phase holographic grating were presented,based on the photo-refractive-like(PR-like) effect.     

Uniaxial stress dependence of the dielectric properties of barium titanate single crystals

BaTiO₃ single crystals were grown by the melt-grown method. The effect of uniaxial pressure (0–1700 bar) on the dielectric properties of these crystals has been systematically studied. The external stress showed obvious effects on these properties. An increase in the difference between the Curie T_c and Curie–Weiss T₀ temperatures induced by the applied pressure is observed. This could be ascribed to the inducing of non-ferroelectric cubic islands in the tetragonal phase by the applied compressive stress. On the other hand, the pressure behavior of thermal hysteresis and the ??/?T vs. T plot strongly suggests that the phase transition changes to second-order type with increasing pressure. The Curie–Weiss constant obtained from a modified Curie–Weiss law strongly decreases with increasing pressure, suggesting that the mechanism of phase transition is going to order–disorder type. An increase in the difference between the Curie T_c and Burn's T_B temperatures with increasing pressure is observed. This could be ascribed to the narrowing of the temperature range on which the Curie–Weiss law is valid. In general, the obtained results are in good agreement with hydrostatic pressure data. Some kind of relaxation near T_c, which is strongly coupled with strain caused by applied compressive stress, is postulated.     

用耦合波方法研究取样光栅的衍射特性

介绍了利用耦合波理论编写计算光栅衍射特性程序的基本思想和主要步骤。利用编写的程序计算并分析了一种用于激光取样光栅TE波和TM波的衍射特性。     

Optimized growth and dielectric properties of barium titanate thin films on polycrystalline Ni foils

Barium titanate(BTO) thin films were deposited on polycrystalline Ni foils by using the polymer assisted deposition(PAD) technique.The growth conditions including ambient and annealing temperatures were carefully optimized based on thermal dynamic analysis to control the oxidation processing and interdiffusion.Crystal structures,surface morphologies,and dielectric performance were examined and compared for BTO thin films annealed under different temperatures.Correlations between the fabrication conditions,microstructures,and dielectric properties were discussed.BTO thin films fabricated under the optimized conditions show good crystalline structure and promising dielectric properties with εr～ 400 and tan δ < 0.025 at 100 kHz.The data demonstrate that BTO films grown on polycrystalline Ni substrates by PAD are promising in device applications.     

Cu∶KNSBN晶体衍射效率的角度选择性研究

耦合波理论是分析光折变晶体的基本方法,由耦合波理论可以得到光折变晶体的衍射效率具有角度选择性。针对这一结论,利用Cu:KNSBN晶体中的双光束耦合,从理论和实验两个角度做了分析,实验结果和理论分析基本吻合。结果表明,对于一定厚度的Cu∶KNSBN晶体,双光束的写入角存在着一个最佳值,使得Cu:KNSBN晶体的衍射效率最大。     

弱谐波情况下透射光栅衍射效率标定方法

同步辐射光源中的高次谐波会使透射光栅衍射效率标定精度变差。为了校正光源中的高次谐波对透射光栅衍射效率标定的影响,提出了一种光源存在弱谐波情况下的透射光栅衍射效率标定方法,通过使用谐波X射线的衍射效率修正基波衍射效率标定中谐波的影响,从而得到更为准确的透射光栅衍射效率。使用该标定方法在北京同步辐射光源上开展了透射光栅相对衍射效率标定工作。实验结果表明:在100~800eV存在高次谐波能段,修正后透射光栅一级与零级的相对衍射效率与理论模拟结果吻合较好,修正后光栅二级与一级的相对衍射效率更接近理论模拟结果,但与理论模拟结果仍有较大偏差,该偏差主要来源光栅较弱的二级衍射。     

全息聚合物弥散液晶材料衍射特性的优化

研究了影响全息聚合物弥散液晶(HPDLC)衍射效率的主要因素，分析了衍射效率与聚合物单体的选择、曝光强度、曝光时间、液晶含量及温度的依赖关系，从而找到最佳条件，使衍射特性得到优化.目前测得的最大衍射效率为802%.实验中还研究了扫描电镜(SEM)观察下HPDLC的表面形貌.     

Effect of barium titanate nanoparticles of different particle sizes on electro-optic and dielectric properties of ferroelectric liquid crystal

A comparative study of two different particle sizes of ferroelectric barium titanate (BaTiO₃) nanoparticles as a dopant on the molecular structure, spontaneous polarization and dielectric behavior of a pure ferroelectric liquid crystal 6F₆T have been studied. It has been found that there is a remarkable decrease in isotropic temperature of both doped samples as compared to the pure 6F₆T sample. The spontaneous polarization also decreases for both the doped samples and the reduction is more pronounced in case of the dopant with large particle size. The dielectric spectroscopy confirms the presence of soft mode as well as Goldstone mode and also shows the decrease in the value of dielectric permittivity ?' as a function of frequency for both doped samples. The improvised properties of liquid crystal host doped with BaTiO₃ nanoparticles mainly depend upon the synthesis method of nanoparticles and also upon the particle size of dopant.     

弱谐波情况下透射光栅衍射效率标定方法

同步辐射光源中的高次谐波会使透射光栅衍射效率标定精度变差。为了校正光源中的高次谐波对透射光栅衍射效率标定的影响,提出了一种光源存在弱谐波情况下的透射光栅衍射效率标定方法,通过使用谐波X射线的衍射效率修正基波衍射效率标定中谐波的影响,从而得到更为准确的透射光栅衍射效率。使用该标定方法在北京同步辐射光源上开展了透射光栅相对衍射效率标定工作。实验结果表明：在100~800 eV存在高次谐波能段,修正后透射光栅一级与零级的相对衍射效率与理论模拟结果吻合较好,修正后光栅二级与一级的相对衍射效率更接近理论模拟结果,但与理论模拟结果仍有较大偏差,该偏差主要来源光栅较弱的二级衍射。     

A system for doing low temperature-high pressure single crystal X-ray diffraction with a synchrotron source

Abstract

A new diamond anvil cell and a helium flow cryostat have been developed for X-ray diffraction on single crystals at low temperatures and high pressures using white radiation of a synchrotron beam. This novel instrument especially enables continuous change of temperature and pressure of the sample without any adjustment of alignment. Automatic search for diffraction peaks can be performed since less than 30 pm eccentricity can be maintained during the rotation of the cell in the cryostat and the rotation of the cryostat on the goniometer head. The minimum temperature reached is 46 K. Measurements of solid 4He at 11.8 GPa are presented which confirm the stability of the hcp phase on this isobar.     

A strong correlation of crystal structure and Curie point of barium titanate ceramics with Ba/Ti ratio of precursor composition

A series of barium titanate powders were synthesized from precursors BaCO₃ and TiO₂ with Ba/Ti ratio ranged from 0.96 to 1.04. For the ceramics sintered at 1300 °C for 2 h, with increasing Ba/Ti ratio from 0.96 to 1.04, the tetragonal distortion of perovskite barium titanate phase was decreased continuously and the Curie point was decreased monotonously from 122.9 to 98.0 °C. At the same time, the content of secondary phases was very low. This correlation of crystal structure and Curie point of barium titanate ceramics was explained by composition variation of the perovskite phase itself rather than by the influence from secondary phases. Due to very controversial results reported by different groups, it was proposed that BaTiO₃ has some different states with different solubilities for BaO and TiO₂. Further investigations should be conducted on the preparation and the properties of BaTiO₃ with much BaO or TiO₂ dissolved.     

Sinc切趾布拉格光栅谱合成特性

谱合成是获得高功率激光输出的有效方法。反射布拉格光栅衍射旁瓣是影响谱合成效率的主要因素。建立了sinc切趾布拉格光栅谱合成理论模型,采用传输矩阵法,分析了光栅参数对切趾光栅衍射特性的影响,以及入射光束光谱宽度和发散角对谱合成效率的影响。计算结果表明：sinc切趾布拉格光栅可有效抑制衍射旁瓣的影响,其一级衍射旁瓣和二级衍射旁瓣的峰值分别由62%和36%下降为0.57%和0.12%。通过优化光栅参数,利用sinc切趾布拉格光栅可实现窄光谱间距、高谱合成效率的多光束谱合成。切趾后,在10 nm的带宽内,参与谱合成光束的数目由7束增加为25束。对于波长为1 064 nm和1 064.4 nm的两束光谱合成,当入射光束光谱宽度小于0.15 nm,且发散角小于0.8 mrad时,谱合成效率达90%以上。     

Sinc切趾布拉格光栅谱合成特性

 谱合成是获得高功率激光输出的有效方法。反射布拉格光栅衍射旁瓣是影响谱合成效率的主要因素。建立了sinc切趾布拉格光栅谱合成理论模型,采用传输矩阵法,分析了光栅参数对切趾光栅衍射特性的影响,以及入射光束光谱宽度和发散角对谱合成效率的影响。计算结果表明：sinc切趾布拉格光栅可有效抑制衍射旁瓣的影响,其一级衍射旁瓣和二级衍射旁瓣的峰值分别由62%和36%下降为0.57%和0.12%。通过优化光栅参数,利用sinc切趾布拉格光栅可实现窄光谱间距、高谱合成效率的多光束谱合成。切趾后,在10 nm的带宽内,参与谱合成光束的数目由7束增加为25束。对于波长为1 064 nm和1 064.4 nm的两束光谱合成,当入射光束光谱宽度小于0.15 nm,且发散角小于0.8 mrad时,谱合成效率达90%以上。     

双掺杂LiNbO3:Fe:Mn体全息光栅的时空衍射特性

通过联立求解两中心带输运物质方程和双光束耦合波方程 ,建立了研究双掺杂LiNbO3:Fe :Mn晶体采用双色光记录光折变体全息的时空特性的动力学模型 .数值计算表明 ,该动态体全息光栅的时空衍射特性与晶体中的折射率光栅相对于干涉场的空间相移有关 ,该空间相移的取值范围为 (-π ,π) ,当空间相移的符号发生变化时 ,双光束之间的能量耦合方向也相应地发生反转 .给出了晶体内的等相位线和光强的重新分布 .     

Analysis of diffraction efficiency of a holographic coupler with respect to angular divergence

We present a method to optimize the Coupling efficiency between two fibers using a Holographic Coupler taking diffraction effect into account. For this we obtain expressions for field distributions at the end facet of a fiber. The results obtained by using the expression is found to be in good agreement with the finite element method in literature, the small deviation is attributed to the negligence of field in the cladding. We then use the Kogelnik theory to obtain useful formulae suitable for diffracted optical elements. The diffraction efficiency expressions are then used to predict the different parameters of Holograting so as to get maximum diffraction efficiency in a direction where the field distribution from the end facet is minimum thereby increasing the coupling efficiency.      

球面波条件下体全息存储的衍射特性分析

从理论上推导了球面波作为参考光和读出光时体全息存储的相对衍射效率和晶体旋转角度之间的关系,对得到的衍射效率的理论公式进行了数值模拟,并且对模拟的结果进行了分析。结果表明,球面波系统的存储容量更高,角度选择性更好,并且有利于系统的小型化。     

双掺杂LiNbO3:Fe:Mn体全息光栅的时空衍射特性

通过联立求解两中心带输运物质方程和双光束耦合波方程，建立了研究双掺杂LiNbO_{3< /sub>:Fe:Mn晶体采用双色光记录光折变体全息的时空特性的动力学模型.数值计算表明，该动态体全息光栅的时空衍射特性与晶体中的折射率光栅相对于干涉场的空间相移有关，该空间相移的取值范围为(-π，π)，当空间相移的符号发生变化时，双光束之间的能量耦合方向也相应地发生反转.给出了晶体内的等相位线和光强的重新分布.}     

Investigation of dielectric properties and diffraction efficiency enhancements caused by photothermal effect in DR9 dye-doped nematic liquid crystal

In this work, we studied dielectric properties and laser-induced refractive index changes originating from photothermal effects of liquid crystal material doped with Disperse Red 9 (DR9) dye. Dye concentration is arranged to be between percentages changing from 0.2 wt.% to 1 wt.% in E63 nematic liquid crystal. Nonlinear optical properties such as diffraction efficiency (η) and refractive index modulation (Δn) were investigated by diffraction grating measurements. It was found the diffraction efficiency of pure E63 nematic liquid crystal is 1%. As the doping amount of DR9 dye in nematic LC is increased, diffraction efficiency took higher values and the maximum diffraction efficiency of 10% was gained with E63 doped with 0.8 wt.%DR9 dye. Moreover, dielectric permittivity and dielectric anisotropy values of the samples were investigated in the frequency range of 100 Hz-10 MHz by using dielectric spectroscopy technique. It was observed that dielectric constant values of the liquid crystal material are strongly affected by doping with dye.