Electrical fixing of 1000 angle-multiplexed holograms in SBN:75

We have demonstrated electrical fixing of 1000 angle-multiplexed holograms in a 1-cm(3)volume Ce-doped SBN:75 crystal. A revealing procedure yielded an average diffraction efficiency of 0.005% for each hologram, with approximately 20% variation. The erasure resistance of the fixed gratings was verified.     

Effect of the parameters on diffraction efficiency after thermal fixing for reflection geometry hologram storage in LiNbO3:Fe

For reflection geometry hologram storage in LiNbO₃:Fe, we have shown that the diffraction efficiency increases with doping level and thickness of storage material monotonically. When the acute angle between reference and z-axis is large enough for getting a relative small Bragg angle that is needed for angle multiplexing, smaller angle does good to diffraction efficiency after thermal fixing. And for absorption coefficient, there is an appropriate value responding to optimal diffraction efficiency after thermal fixing and we develop a theoretical model that predicts achievable diffraction efficiency after thermal fixing as a function of crystal thickness, doping level, acute angle between reference and z-axis and absorption coefficient. We compare this model with experiment results and get a good agreement.     

Self-enhanced diffraction properties of a nominally undoped barium titanate crystal with a thermally fixed grating

We describe recent studies on diffraction properties of a photorefractive barium titanate crystal having a thermally fixed grating. Buildup dynamics of diffracted signals are measured to analyze the contributions of ionic and re-created photocarrier (hole) gratings to the temperature-dependent diffraction efficiency in self-enhanced readout. An activation energy of mobile ions as nonphotoactive secondary carriers for fixing volume holograms is determined holographically. This value is compared with that of hydrogen ions estimated from polarization-dependent infrared absorption spectra in order to indentify the fixing species.     

（Ce，Cu）：LiNbO3晶体非挥发全息记录理论研究与优化

根据双中心带输运模型，对（Ce，Cu）：LiNbO3晶体双中心非挥发全息记录进行了理论研究与优化。推导了（Ce，Cu）：LiNbO3晶体的微观参量，采用数值方法通过严格求解模拟双中心带输运方程来模拟全息记录过程。分析了记录过程中，记录与敏化光强、Ce和Cu掺杂浓度以及晶体微观参量对（Ce，Cu）：LiNbO3晶体双中心全息记录的影响。发现（Ce，Cu）：LiNbO3晶体非挥发全息记录中实现高衍射效率与固定效率的主导因素是深中心Cu，在记录过程中，深中心Cu建立起了很强的空间电荷场。数值模拟的结果经过实验验证，最高饱和与固定衍射效率别为60．5％和53．8％。     

Effects of applied DC/AC fields in electrical fixing process with SBN:60

We present experimental investigations of electrical fixing techniques in Ce:SBN:60. The effect of crystal fatigue on the diffraction efficiency of electrically fixed photorefractive gratings is studied. We observed that applying an ac field to the crystal eliminated crystal fatigue and improved diffraction efficiency. A controllable diffraction efficiency of a photorefractive grating is presented. A reproducible diffraction efficiency of up to 75% is obtained using a write-reveal grating technique with high-voltage pulses of opposite polarity. We also show that the diffraction efficiency can be controlled by varying the intensity of the writing beams incident to the crystal during the recording process. A method of determining the hysteresis loop using the domain-fixing technique is proposed. The dependence of the diffraction efficiency on the direction of the applied electric field while writing the hologram is studied. Our experiments show that, during writing, when the electric field is applied opposite to the c axis the grating can be successfully revealed with both positive and negative dc voltages. However, when the grating is written with a field parallel to the c axis, the grating can be revealed only with a field applied in the opposite direction. Received: 28 October 2002 / Revised version: 28 February 2003 / Published online: 14 May 2003 RID="*" ID="*"Corresponding author. Fax: +1-812/872-6167, E-mail: azad.siahmakoun@rose-hulman.edu     

LiNbO3中光折变全息的热固定特性

带输运模型方程和耦合波方程结合起来研究ＬｉＮｂＯ３晶体中体全息记录和热固定的特性。发现在一边记录一边固定时,同时存在的离子光栅通过减小耦合增益而影响了电子光栅的写入,且得到的固定后折射率光栅随深度的改变较小,这与记录完固定有非常大的区别,两种热固定方法得到的折射率光栅的衍射效率大小将主要决定于入射记录的实始光强比,该模型同时显示对于高掺杂浓度的ＬｉＮｂＯ３晶体的热固定,在其显影过程中,由于导带电子     

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.     

BaTiO3晶体中体全息栅的高效热定影

报道了对ＢａＴｉＯ３晶体中体全息栅的热定影过程的研究结果，对ＢａＴｉＯ３晶体中离子补偿栅形成的临界温度，离子栅的形成与衍射光振荡间的关系，离子栅的形成速度与温度的关系，降温方式对热定影效率的影响进行了仔细的研究，并实现了高效率的热定影，发现了高温擦除过程的有趣现象，并对实验结果进行了分析。     

Diffraction efficiency increase by corona discharge in photoinduced surface-relief gratings on an azo polymer film

The diffraction efficiency of a surface-relief grating (SRG) was dramatically increased by corona discharge. We fabricated this SRG by applying surface modulation to azo polymer films, using laser interference fringes. The electric charge was deposited upon the SRG by a corona discharge in an oven. The first-order diffraction efficiency measured before and after corona discharge above the glass-transition temperature increased from ~2% to ~40% in a SRG written with a circularly polarized beam. The relief depth of the SRG as measured with an atomic-force microscope also increased, from ~130 nm to ~450 nm. The increase in diffraction efficiency was independent of the writing polarization.     

光色效应(Fe,Mn)\:LiNbO3晶体非挥发性全息存储中自衍射效应的实验研究

在双掺杂 (Fe ,Mn)…LiNbO3 晶体光色效应非挥发性全息存储实验中 ,观测到光束耦合作用导致的自增强和自衰减效应。根据这种自衍射效应 ,归纳了四种记录和光固定实验组合方案。实验结果表明 ,在记录和光固定过程中利用自增强效应得到的最高衍射效率为利用自衰减效应得到的衍射效率的两倍左右 ,说明在实际应用中必须考虑和利用自增强效应。     

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.     

STUDY OF THE FOUR-WAVE MIXING DIFFRACTION EFFICIENCY OF LONGITUDINAL-FIELD MULTIPLE-QUANTUM-WELL PHOTOREFRACTIVE DEVICE GROWN AT LOW TEMPERATURE

We investigate the relationship between the beam intensity and the four-wave mixing diffraction efficiency of longitudinal-field multiple-quantum-well(LMQW) photorefractive device grown at low temperature. The optimum beam intensity is found. We also explain the different mechanisms of the effect of beam intensity on the diffraction efficiency of the LMQW device and the transverse-field MQW device. Some advice on how to improve the diffraction efficiency is given.     

中子衍射分析时效处理对镍基单晶高温合金相结构的影响

采用φ振荡和φ固定两种数据采集模式的中子衍射实验结果表明较高的时效温度对消除枝晶最有效,微应变(晶粒区域间的变形不协调性)主要存在于γ'相.利用中子衍射结合扫描电子显微镜对合金的微观组织形貌进行了细致观察,给出了时效温度和时间对γ'相的影响状况,超晶格测量发现了γ'相晶粒之间出现的独特取向差.由不同晶面的中子衍射结果判断时效后合金出现了轻微的四方对称性(a < c)畸变,对这种畸变起主要作用的是基体相.实验结果同时证实了不同方向的应变差异,因而为筏化驱动模型的定量 关键词： 单晶高温合金 中子衍射 超晶格 时效处理     

一种嘧啶铱（Ⅲ）配合物的结构及光电性质研究

合成了一种铱配合物（DFPPM=2-（2,4-二氟苯基）嘧啶,acac=乙酰丙酮）,利用 X 射线单晶衍射仪测定了该化合物的晶体结构。利用紫外-可见吸收光谱、发射光谱对其光物理性质进行研究。结果表明：（DFPPM）₂ Ir（acac）的单晶结构属于三斜晶系,P-1空间群,晶胞参数a=14.444 4（7）nm,b=18.047 9（10）nm,c=19.220 0（9）nm,α=113.115（5）°;,β=90.453（4）°;,γ=90.989（4）°;,V=4 607.0（4）nm³。（DFPPM）₂ Ir（acac）在二氯甲烷溶液中的发射峰为 496 nm。以（DFPPM）₂ Ir（acac）为客体材料,制备了结构为ITO/NPB（40 nm）/CBP：（DFPPM）₂Ir（acac）（质量分数10%,30 nm）/TPBi（15 nm）/Alq₃（50 nm）/Mg：Ag（150 nm,10：1）/Ag（10 nm）的器件,器件的发射峰位于494 nm,最大亮度达到21 400 cd/m²,最大电流效率为12.0 cd/A,最大功率效率为 5.4 lm/W。     

Cross-link optimized cascaded volume hologram array with energy-equalized one-to-many surface-normal fan-outs

Achieving a uniform fan-out energy distribution is critical to the successful applications of substrate guided-wave optical interconnects. Using Dupont photopolymer film HRF-600X00120, we investigated the optimum recording beam intensity for obtaining a large dynamic region of diffraction efficiency relative to exposure dosage. Based on the experimental diffraction efficiency curve, 1-to-5 and 1-to-9 surface-normal fan-out devices were fabricated that operated at a wavelength of 850nm, and output nonuniformities of +/-4 % and +/-10 % were obtained for the two devices.     

UHU adhesive holograms replication

It is possible to apply a new recording material with high diffraction efficiency (of the order of 82.3%) to replicate computer phase or analogical holograms. This material is the all purpose adhesive UHU^®. It is constituted by some components of polyvinyl, nitrates and some solvent agents; it is easily applied to any substrate. We record this material with heat generation by hand rubbing, using a mask (Kodalith^® films) manufactured with lithographic techniques. The holographic replication is excellent on the new material UHU^® adhesive, showing a phase modulation for refraction index and relief. This modulation is determined by the cured polymers process induced by friction, as pressure and temperature, with an anaerobic reaction.For copy of conventional holograms at high frequencies (holographic ranges), the diffraction efficiency parameter is in the neighborhood of 19.1% at first order or more, depending on diffraction efficiency of the pattern of the hologram. The hologram is elaborated in the absence of any development process and does not need to have carefully controlled conditions of the environment. Following this process, the hologram is obtained at standard atmospheric conditions of pressure and temperature.     

Diffraction efficiency of localized holograms in doubly doped LiNbO(3) crystals

The diffraction efficiency of M holograms superimposed in the volume of the recording medium is proportional to 1/M(2). We present a method, based on nondestructive localized holograms in a doubly doped LiNbO(3) crystal, that allows us to also record M holograms in the same volume without an exposure schedule or a diffraction efficiency that has 1/M dependence. We compare experimentally the final diffraction efficiency obtained with the localized and distributed recording methods.     

High diffraction efficiency and a quasi-permanent grating in photorefractive nematic liquid crystal at low temperature

At a temperature lower than the melting point of pure pentyl-cyanobiphenyl liquid crystal (5CB) we studied the photorefractive effect of 5CB heavily doped with fullerene (C60) and obtained a diffraction efficiency of the photorefractive grating of more than 40%, which is more than twice as high as the best data reported to our knowledge. A quasi-permanent grating was observed with a diffraction efficiency of 11.2% after the grating was kept in the dark for a month.     

Achromatic diffraction from polarization gratings with high efficiency

We demonstrate a broadband, thin-film, polarizing beam splitter based on an anisotropic diffraction grating composed of reactive mesogens (polymerizable liquid crystals). This achromatic polarization grating (PG) manifests high diffraction efficiency (approximately 100%) and high extinction ratio (> or = 1000:1) in both theory and experiment. We show an operational bandwidth Deltalambda/lambda0 approximately 56% (roughly spanning visible wavelength range) that represents more than a fourfold increase of bandwidth over conventional PGs (and significantly larger than any other grating). The diffraction angle and operational region (visible, near-infrared, midwave infrared, and ultraviolet wavelengths) may be easily tailored during fabrication. The essence of the achromatic design is a stack of two chiral PGs with an opposite twist sense and employs the principle of retardation compensation. We fully characterize its optical properties and derive the theoretical diffraction behavior.