畴腐蚀掺镁铌酸锂可调阵列光分束器的研究

研究了不同畴腐蚀深度的掺镁铌酸锂二维六角可调阵列光分束器的分数Talbot效应.对不同Talbot分数β和不同畴腐蚀深度的阵列光分束器Talbot衍射像进行了数值模拟理论研究.模拟结果表明,Talbot分数β可以改变Talbot衍射像的周期及结构分布,而畴腐蚀深度可有效调制衍射像的光强分布.在理论研究的基础上,设计并制备了具有不同畴腐蚀深度的掺镁铌酸锂二维六角阵列光分束器,对其在不同Talbot分数β条件下的分数Talbot效应进行了通光实验研究,实现了畴腐蚀阵列光分束器对近场Talbot衍射光强分布的调制,实验结果与理论研究结果一致.     

畴腐蚀掺镁铌酸锂光分束器的泰伯效应研究

基于菲涅耳衍射理论分析了畴腐蚀二维周期结构掺镁铌酸锂晶体光分束器的泰伯效应,对光分束器不同占空比D及泰伯分数β条件下的近场光衍射自成像进行了数值模拟研究。设计并制备了不同占空比的畴腐蚀掺镁铌酸锂晶体光分束器,并对其进行了分数泰伯光衍射自成像的实验研究,得到了不同泰伯分数β条件下的近场光衍射强度分布。结果表明,当光分束器占空比D=52%、泰伯分数β=2时,近场衍射自成像效果最佳,实验结果与理论研究结果相符。     

基于周期极化掺镁铌酸锂晶体的六角可调相位阵列光栅

研究了基于周期极化掺镁铌酸锂(PPMg…LN)晶体的二维六角可调相位光栅及其Talbot效应光衍射成像。理论模拟不同相位差及分数Talbot距离条件下的近场光衍射强度分布,计算取样区内衍射强度随相位差和分数Talbot距离的变化,给出相位差恒定及变化情况下取样区强度最大值的位置。在理论研究基础上,设计与制备PPMg…LN六角可调相位阵列光栅,并进行了Talbot衍射成像的实验研究,实验结果与理论研究吻合较好。     

外加电场调制二维六角位相阵列光分束器的研究

本文建立了外加电场调制二维六角位相阵列光分束器的倒格矢理论模型, 利用数值模拟方法开展了阵列光分束器的理论研究, 对可调位相差阵列光分束器进行了分析, 得到了不同分数泰伯距离以及外加电场条件下的光强分布图. 实验设计与制备了铌酸锂二维六角位相阵列光分束器, 并对其进行了Talbot衍射光分束实验研究, 当外加电压为0.5 kV(电场为1 kV/mm)时, 观测到了Talbot衍射光分束现象, 随着外加调制电场的增大, 其衍射光分束图像越清晰, 该实验结果和理论研究结果相符.     

利用光衍射效应探测周期极化微结构晶体

以光栅衍射理论为基础，从理论上分析研究了微结构晶体衍射效率与占空比和折射率的关系.采用波长为532nm，最大功率为80mW 的连续激光为光源，分别对周期极化掺镁铌酸锂微结构晶体和周期极化同成分铌酸锂微结构晶体的占空比及极化反转引起的折射率变化进行了测试.测试结果表明，掺镁铌酸锂晶体周期极化反转所引起的折射率改变量大于同成分铌酸锂晶体极化反转所引起的折射率变化. 关键词： 光栅衍射 占空比 折射率变化     

基于分数Talbot效应的棋盘格状阵列照明器北大核心CSCD

基于分数Talbot效应,利用纯位相光栅设计了一种二维棋盘格状阵列照明器。利用菲涅尔衍射理论分析了平面光波照射下纯位相光栅衍射光场,得到位相调制为(0,π/2)的二阶纯位相光栅可以实现压缩比为2的棋盘格状阵列照明。利用二元光学器件制作技术,在光学玻璃基底上制作了位相光栅。在扩束激光光束照射下,在分数Talbot距离处获得了效率为83.2%的棋盘格状明暗相间光斑阵列。实验结果很好地验证了理论分析结论。研究结果对于光互连、光通信、光电混合处理领域中阵列微光束生成和应用都具有较高的理论和实用价值。     

掺铁铌酸锂晶体的光电导衰减特性研究

利用电化学分析仪对掺铁同成分铌酸锂晶体进行瞬态光电导研究. 以不同掺铁浓度铌酸锂晶体为样品, 在不同强度的纳秒级脉冲光照射下对光电导的研究发现: 铌酸锂晶体的瞬态光电导是由较为复杂的电子迁移过程形成, 其衰减可以用一个指数函数叠加一个扩展指数来拟合. 拟合参数与光强、掺铁浓度存在以下依赖关系: 入射光强增强时, 幅值σ₁^max、σ₂^max、时间常数τ₂和扩展因子β 值增大, 在光强增大到一定时, τ₂和β出现饱和; 晶体的掺铁浓度升高时, σ₁^max、σ₂^max、τ₂ 值增大, 而β值减小. 根据实验结果, 从理论上提出了光电子导带迁移伴随光电子在小极化子上跳跃迁移的复合电荷传输模型. 该模型较好地解释了掺铁同成分铌酸锂晶体的光电导的衰减特点.     

同成分掺镁铌酸锂晶体紫外光致吸收阈值效应的研究

研究了同成分掺镁铌酸锂晶体中的紫外光致吸收效应。通过对不同掺Mg浓度铌酸锂晶体的紫外光致吸收系数和双色存储灵敏度的测量,发现同成分掺镁铌酸锂晶体的紫外光致吸收效应具有Mg离子浓度阈值效应。只有当掺Mg摩尔分数大于3．0％时,从近紫外一直延伸到近红外波段的紫外光致吸收效应才显示出来。这一Mg离子浓度阈值效应进一步为双色存储灵敏度的测量结果所证实。该浓度阈值小于掺镁铌酸锂晶体抗光损伤效应的摩尔分数阈值4．6％。这种紫外光致吸收现象可能和掺镁铌酸锂晶体中反位铌NbLi浓度的急剧减少基本消失有关。     

掺杂对铌酸锂晶体非挥发全息存储性能的影响

通过研究掺镁、掺锌和掺铟同成分铌酸锂晶体的紫外-红光双色全息存储性能,发现双色记录响应时间均比单色记录时明显缩短,最多的可减小3个数量级;双色记录灵敏度大幅度提高,在掺镁5 mol.%的晶体中可达到11 cm/J.在掺杂浓度超过抗光损伤阈值的铌酸锂晶体中,均可实现非挥发全息存储.但是,在掺镁、锌样品中,深、浅能级中心上的光栅反相,而在掺铟样品中则表现为同相.这是由于掺杂离子的种类不同,在铌酸锂晶体中形成的缺陷中心也不同所引起的. 关键词： 掺杂 铌酸锂晶体 非挥发 全息存储     

掺镁铌酸锂亚微米结构畴反转的研究

研究了掺镁铌酸锂(MgO：LiNbO₃)的极化特性及其畴壁运动的性质,通过调节多个脉冲外加电场来控制畴壁的运动,在背向反转效应作用下,反转畴发生劈裂,制备出均匀的掺镁铌酸锂亚微米周期畴结构,并分析探讨了掺镁铌酸锂亚微米结构的成因及其反转机理. 关键词： 亚微米畴结构 掺镁铌酸锂 背向反转     

Diffractive self-imaging based on selective etching of a ferroelectric domain inversion grating

A hexagonal array grating based on selective etching of a 2D ferroelectric domain inversion in a periodically poled Mg O-doped Li Nb O3 crystal is fabricated. The effects to the diffractive self-imaging as a function of diffraction distance for a fixed phase difference and array duty cycle of the grating is theoretically analyzed.The Talbot diffractive self-imaging properties after selective etching of a 2D ferroelectric domain inversion grating under a fixed phase difference are experimentally demonstrated. A good agreement between theoretical and experimental results is observed.     

ZnS:Ag的ESR及结构相变研究

ESR实验表明Ag在ZnS微晶中是以Ag⁺离子的形式存在,没有测到Ag²⁺离子的信号.以Mn²⁺为探针的ESR和X射线衍射分析研究发现,在ZnS微晶由立方点阵(β相)变为六角点阵(α相)的结构相变中,Ag⁺离子对相变的影响与掺杂浓度和煅烧温度有关,当掺Ag量为5×10^-4g/g时相变在1100~1200℃出现逆转现象.由Mn²⁺的ESR谱得出α相的朗德因子g为2.006,越精细常数a为6.76mT,β相的g为2.002,a为6.81mT.     

Analysis of period and visibility of dual phase grating interferometer

Dual phase grating interferometer may simultaneously achieve large field of view and high x-ray dose efficiency. Here, we develop a simple theoretical method to better understand the imaging process of the dual phase grating interferometer. The derivation process of fringe period and the optimal visibility conditions of the dual phase grating interferometer are given in detail. Then, we theoretically prove that the fringe period and optimal visibility conditions of the dual phase grating interferometer include that of the Talbot interferometer. By comparing our experimental results with those of other researchers, we find that when the positions of phase gratings are far away from the positions where the fringe visibility is optimal, the fringe period of the dual π -phase grating interferometer is twice the theoretical results under the illumination of polychromatic x-ray. This conclusion may explain the contradictory research results of dual phase grating interferometer among different researchers.     

Unveiling Talbot Effect under Fresnel Diffraction at a Fork-Shaped Grating

The near-field effect of diffraction image self-reproduction or self-imaging of a periodic grating illuminated by quasi-monochromatic wave is well-known as the Talbot effect. Introducing a dislocation to a periodic structure provides a fork-shaped modulation of the phase/amplitude, which produces discrete diffraction pattern in a far-field consisting of optical vortices. In this paper, Fresnel diffraction at amplitude fork-shaped grating is theoretically and experimentally studied. The coexistence of spatial ordering and local violation of translational symmetry of the structure manifests itself in a strict diffraction pattern consisting of optical vortices in the far-field, which is shown to be accompanied by formation of a spatially ordered intensity distribution in the near-field, reminiscent the Talbot carpets for periodic structures. These results demonstrate the first evidence of Talbot effect occurred under light diffraction at fork-shaped gratings, being promising for deep understanding of near-field singular optics phenomena.     

Attempt to generalize fractional-order electric elements to complex-order ones

The complex derivative D~(α±jβ), with α, β∈ R+ is a generalization of the concept of integer derivative, where α = 1,β = 0. Fractional-order electric elements and circuits are becoming more and more attractive. In this paper, the complexorder electric elements concept is proposed for the first time, and the complex-order elements are modeled and analyzed.Some interesting phenomena are found that the real part of the order affects the phase of output signal, and the imaginary part affects the amplitude for both the complex-order capacitor and complex-order memristor. More interesting is that the complex-order capacitor can do well at the time of fitting electrochemistry impedance spectra. The complex-order memristor is also analyzed. The area inside the hysteresis loops increases with the increasing of the imaginary part of the order and decreases with the increasing of the real part. Some complex case of complex-order memristors hysteresis loops are analyzed at last, whose loop has touching points beyond the origin of the coordinate system.     

Generation of near-field hexagonal array illumination with a phase grating

A hexagonal array not only is a nature-preferred pattern but also is widely used in optoelectronical materials and devices. We report a simple method of hexagonal array illumination based on the Talbot effect that has a theoretical efficiency of 100%. An experimental efficiency of 90.6% with a binary phase (0, pi) hexagonal grating is given. This method should be highly interesting for applications of hexagonal array illumination in optical devices as well as in other hexagonal cells.     

定向凝固单晶冰的取向确定与选晶

基于六方冰晶偏振光学特性,定义了用于确定冰晶晶体取向的三个参数:光轴倾角α,消光角β和与冰晶基面(0001)面内晶体学择优方向1120与温度梯度的夹角γ,提出了定量判定冰晶晶体取向的理论基础,并在定向凝固平台上采用偏光显微镜成功实现了冰晶晶体取向的精确主动控制,获得了任意取向的单晶冰.本文成功解决了冰晶的定向凝固晶体取向确定和选择的难题,为冰晶生长过程中相关理论问题的研究提供了有效的途径.     

极端条件下锆的动力学稳定性研究

过渡金属Zr具有优良的物理、化学及力学性能, 具有广泛的应用价值. 主要通过新近发展的自洽晶格动力学方法, 充分考虑声子间的相互作用, 成功获得了β-Zr的高温高压声子色散曲线, 预测了β-Zr在相图中能够稳定存在的区域, 进一步比较α-Zr, ω-Zr和β-Zr的自由能, 获得了α-β 及ω-β 相变的相边界, 构建了Zr的参考相图. 同时, 也获得了β-Zr的高温状态方程及热膨胀系数, 能够为构建Zr的全区物态方程提供有益的参考.