LiNbO_3∶Ce∶Cu晶体中绿光非挥发全息记录优化

为了对在LiNbO3∶Ce∶Cu晶体中绿光作为记录光的非挥发全息记录进行优化,联立求解了双中心物质方程和双光束耦合波方程,数值分析了平均空间电荷场(SCF)和衍射效率随晶体的氧化还原态、记录光与敏化光的光强比以及深浅中心的掺杂浓度的变化。结果表明,采用绿光作为记录光在LiNbO3∶Ce∶Cu晶体中进行非挥发全息记录,可以记录得到强光折变光栅,其空间电荷场高达107V/m;获得高达80%以上的固定衍射效率,各相关参量都有较大的优化空间。     

LiNbO3:Ce:Cu晶体中绿光非挥发全息记录优化

为了对在LiNbO3:Ce:Cu晶体中绿光作为记录光的非挥发全息记录进行优化,联立求解了双中心物质方程和双光束耦合波方程,数值分析了平均空间电荷场(SCF)和衍射效率随晶体的氧化还原态、记录光与敏化光的光强比以及深浅中心的掺杂浓度的变化.结果表明,采用绿光作为记录光在LiNbO3:Ce:Cu晶体中进行非挥发全息记录,可以记录得到强光折变光栅,其空间电荷场高达107V/m;获得高达80%以上的固定衍射效率,各相关参量都有较大的优化空间.     

光学自增强效应与衍射效率的提高

利用含时光折交双光耦合方程数字模拟计算了掺铁铌酸锂晶体中双光耦合的动态过程,分析了空间电荷场及其位相、光折交光栅位相等光折交参量的变化过程,解释了光折变自增强效应,提出了提高光折交光栅衍射效率的有效方法．     

双掺杂LiNbO3晶体中光栅均匀性的优化研究

研究了非挥发全息记录中南于紫外光的强吸收而引起的光栅非均匀性，分析了这种非均匀性对光栅衍射效率的影响。结果显示，非均匀性致使光折变光栅的平均强度减弱，衍射效率降低。提出了采用两束等光强的敏化紫外光由晶体两侧入射的优化方案以改善光栅的均匀性，提高光栅的衍射效率。通过联立两中心带输运物质方程和双光束耦合波方程，进行了相应的理论模拟，并给出实验验证。结果表明双侧紫外光照射能够实现均匀性较好的光栅，是提高衍射效率的有效途径之一。     

光折变局域体全息柱透镜变波长读出下的波前转换

研究了用波长为632.8nm的柱面波与平面波记录形成的体全息柱透镜用波长为800nm的平面波重现下的波前转换情况。结合二维耦合波理论,推导了形成于LiNbO3双掺杂晶体中该全息柱透镜的耦合波方程,并求出了其积分形式的解析解,分析了改变读出波长下该透镜的布拉格失配因子的分布情况,讨论了它的几何尺寸和记录柱面光波对其衍射效率的影响,以及柱面衍射光振幅在出射口径上的分布情况。结果表明,记录所形成的全息柱透镜的焦距越长它的衍射效率越高;该透镜厚度的增加会使它的衍射效率增加,但是透镜的衍射口径增加它的衍射效率会降低;衍射光振幅在其出射口径上的分布出现了一定程度的失真,衍射光强度主要集中分布在布拉格失配值较小处对应的位置。最后,进一步讨论了全息透镜记录过程中满足布拉格匹配条件的参考点的选择对光栅衍射性质的影响,结果表明衍射效率不随参考点的改变而改变。     

基于FlexPDE研究顺电相KTN晶体中大调制度全息光栅的形成

在用带输运模型研究光折变效应时,大多数情况下都限定入射的相干光调制度远小于1,对方程做线性化近似以便于求解,这在求解小调制度问题时可以达到满意的精度。但在很多实际情况下光调制度接近于1,此时线性理论不再适用。基于FlexPDE程序提出了一种新的求解方法,适用于大调制度时的情况。采用有限元算法,严格求解光折变带输运方程,研究了外加电场时顺电相KTN晶体中大调制度全息光栅的形成,给出了晶体中的空间电荷场、光激发电子、离化施主、晶体折射率等的分布情况和时间演化曲线。计算结果表明,采用FlexPDE程序不仅可以大大降低带输运模型的求解难度,而且能够实时动态显示全息光栅的形成过程,具有直观性。     

光学自增强效应与衍射效率的提高

利用含时光折变双光耦合方程数字模拟计算了掺铁铌酸锂晶体中双光耦合的动态过程,分析了空间电荷场及其位相、光折变光栅位相等光折变参量的变化过程,解释了光折变自增强效应,提出了提高光折变光栅衍射效率的有效方法．     

局域体全息光栅的理论和应用研究

介绍了国内外局域体全息光栅的理论分析方法、衍射性能的研究和应用情况。重点介绍了局域体全息光栅的耦合波理论方法及其在设计基本光学元件、光通信、集成光学等方而的应用及其发展现状。     

基于耦合波理论的体全息光栅衍射效率计算

基于耦合波理论,对反射体全息光栅的衍射效率进行了计算。给出了体全息图的边界条件,同时对基于耦合波理论的体全息光栅衍射效率的计算结果进行了分析。以便能为制作具有高衍射效率,低噪声的全息光栅做好准备。     

一种测量体光栅调制度和有效厚度的新方法

以Kogelnik的体相位光栅耦合波理论为基础,通过测量光折变体光栅的衍射效率与布喇格偏移角的关系曲线,并根据该曲线的3dB带宽和旁瓣峰值的相对大小及其角度偏移量,可计算出光折变体光栅的折射率调制度和有效厚度。对LiNbO3：Fe晶体的实验测量结果很好地验证了该方法的可行性,其测量精度与数字全息术和马赫一曾德干涉仪的方法相当,但测量过程却更加简单。     

体光栅的垂直选择角和光栅简并

从理论和实验上探讨了体光栅在垂直方向的角度选择性，根据ｋ矢量球与参考点源平面上的对应关系，导出了垂直方向的选择角，并得到光栅简并线方程。实验结果表明体光栅在垂直方向具有有限的选择角     

存储于同一空间点的两幅光折变相位栅交扰问题的研究

给出了利用角度复用技术同时存储两幅光栅于光折变记录介质同一空间点上的稳态空间电荷场解析表达式。发现第一幅光栅的基频分量中含有第二幅光栅的二阶分量的交扰 ,而其二阶分量中却含有第二幅光栅的基频分量的交扰。发现空间电荷场基频分量、二阶分量随归一化的光栅波矢 (k/k0 )变化的最大值偏离了单幅存储时的最大值 ,以及第二幅光栅的自身变化对第一幅光栅的二阶分量的交扰影响远大于其对第一幅光栅的基频分量的交扰影响。同时还发现了调制度m只影响空间电荷场的振幅 ,并不影响空间电荷场随k/k0 变化的极值点位置。     

Fabrication of blazed gratings used in ultraviolet region by holographic ion beam etching based on photoresist melting

A novel technology to manufacture holographic ion beam etched diffraction gratings based on surface therrnokinematics is presented. The surface roughness of photoresist gratings is solved by this technology. According to this technology, a holographic ion beam etched blazed grating of 1200 l/mm for use in the ultraviolet region is manufactured. The experimental results show that the grating has good surface quality, low stray light and high diffraction efficiency. In addition, the performance of thes gratings satisfies the operating requirements of ultraviolet spectrograph.     

Theoretical investigation of 2D periodic nanoplasmon structures

The problem of diffraction of electromagnetic waves by 2D periodic metal gratings is solved with allowance for the finite permittivity of a metal in the optical band. The developed mathematical model is based on the solution of the vector integro-differential equation of diffraction by 3D dielectric bodies by means of the Galerkin method. It is noted that the dependence of the scattered field amplitude on the wavelength has a resonance character and that the resonance wavelengths can substantially exceed the dimensions of a grating cell. The application of the method of approximate boundary conditions for the calculation of gratings containing nanodimensional metal layers is justified. It is demonstrated that a grating with small reflection and transmission factors under the plasmon-resonance conditions can be created.     

一种波分解复用技术的实验研究

文章提出一种基于光折变晶体LiNbO3的波分解复用技术实验研究方法,研究了影响光栅衍射效率的重要因素.实验采用o光写入e光读出,写入光强比为1∶1.通过在同一位置由红光和绿光先后写入光栅(两光栅夹角为0.18°时不会发生串扰),并用耦合光读出,成功地进行了解复用实验.     

An electron-hole transport model for the analysis of thephotorefractive harmonic gratings

The steady-state exact solution for the higher harmonic gratings that synthesize the space-charge field is derived without restrictions within an electron-hole transport model which allows the behavior of these harmonic gratings to be determined rigorously in terms of the main photorefractive parameters. The model predicts the independence of the fundamental and harmonic amplitudes on the average excitation intensity. With respect to the modulation depth m, the dependence of each ν-harmonic order is established as m^ν which is the result obtained in the single-level model. In terms of the grating spacing, three regions of quite different behavior are identified as the linear, transition, and nonlinear regions. The extent of each region in terms of Λ strongly depends on the acceptor density relative to the donor density. If the acceptor density is much greater or smaller than the donor density, the linear region spreads out toward the lowest spacing, the nonlinear region extends toward the highest spacing, and the intermediate region is located in-between, as in the Kukhtarev model. But, for similar concentrations, the nonlinear region is shifted toward smaller spacing with respect to the linear region. On the other hand, the electron-hole competition can be deleterious for recording the grating, due to the charge compensation produced by the additional charge carrier that screens the internal space-charge field. Also, the relative importance of the higher harmonics is apparent for the smallest values of the external field as in the single-level model     

结构参量对脉冲高斯光束布拉格衍射特性的影响

利用二维耦合波理论,研究了体光栅对时间和空间都为高斯型分布的脉冲激光光束的衍射性质,得到了衍射和透射光振幅的解析表达式.讨论了体光栅的结构参量对衍射光束的空间和频谱强度分布以及衍射效率的影响.结果表明,体光栅的波长选择带宽和衍射光束带宽随着结构参量的增大而增大,衍射效率随着入射脉冲时间宽度的增大而增大,并趋于定值,结构参量值越小,达到饱和的速度越慢,饱和值越大.     

利用栅增强技术提高光折变多重存储衍射效率

提出了一种结合折射率栅自增强读出和固定技术的光折变多重存储的记录方法,利用自增强读出时折射率栅在记录晶体中（ｚ向）移动的特点,把同一位置记录的不同全息图的折射率置于晶体中ｚ方向分离的位置,最大限度的利用了晶体各处的折射率的最大动态范围,提高了多重存储衍射效率。     

Photorefractive harmonic gratings within the shallow trap model

The steady-state solutions for higher harmonic gratings that describe the space-charge field in photorefractive materials are derived without restrictions within the shallow trap model. The analysis emphasizes that the amplitudes of the higher harmonic gratings appear strongly for increasing values of both the modulation depth and the grating spacing, and for decreasing values of the external static field as in the Kukhtarev single-species model. However, unlike this early model, the harmonic field amplitudes increase as the average excitation intensity increases. The efficient accumulation of charge carriers in the shallow traps,. due to high density and low thermal excitation rate of shallow centers, also enhances the amplitudes of higher harmonic gratings.