偶氮苯衍生物的全息光存储和双折射特性研究

对6-(4-((4-(十八烷氧基-)苯基)二氮烯基)苯氧基)-1-己醇(E-1-ol)的光致变色、双折射和全息光存储特性进行了研究.以488 nm的氩离子(Ar+)激光为抽运光,632.8 nm 的氦氖(He-Ne)激光为探测光,研究了透射信号强度随时间的变化关系;在10 mW～160 mW的范围内,研究了透射信号强度的最大值随抽运光功率的变化;经计算,在各抽运光功率下,获得的光致双折射值(δn)达10-2量级,最大激光功率下,获得的δn为2.8×10-2.对透射信号强度随时间的变化曲线进行了理论拟合,得出曲线的上升和下降符合双指数增长和衰减,时间响应常量分别是:上升阶段:t1=4.8 s,t2=85.8 s;下降阶段:t1=1.9 s,t2=27.6 s.用等强度s偏振的两束Ar+激光为写入光, He-Ne光为读出光,研究了衍射信号强度随时间的变化及写入光功率改变时,衍射信号强度最大值与写入光功率的变化关系;对衍射信号强度随时间变化的动力学过程进行了理论拟合,得出光栅生长和衰减也有快和慢两个过程,光栅生长时间响应常量为:t1=3.9 s,t2=33.9 s,光栅衰减时间响应常量为 t1=1.8 s,t2=60.1 s.     

SA/PMMA的可擦除光存储特性研究

用在聚甲基丙烯酸甲脂（PMMA）中掺杂邻羟基亚甲基苯胺（SA）样品，实现了可见光区域的可擦除光存储。以Ar^ 激光488.0nm线为写入光，He-Ne激光632.8nm线为读出光，研究了光栅生长的动力学过程。在写入和擦除过程中，均观察到了衍射信号随时间先增强后减弱的趋势。探讨了写入光和擦除光功率对衍射信号的影响，依据相干光调制形成相位光栅和光异构产生压力梯度引起分子扩散的光物理过程对光存储机制进行了探讨。     

甲基红染料掺杂的聚乙烯醇薄膜光存储特性的实验研究

用2倍频小型YAG激光(532nm)作为写入光和擦除光,用He-Ne激光器623.8nm线作为读出光,用CCD作为探测器,研究了不同写入光功率下,甲基红/聚乙烯醇(MR/PVA)薄膜光栅生长的动力学过程和不同擦除光功率下,光栅擦除的动力学过程.结合光栅生长曲线的波动现象,对光存储机制进行了新的探讨.实验发现,两写入光和读出光的功率配比为1:1:1时,可获得最大衍射效率,提出读出光对写入过程具有双重作用的物理模型,对此实验结果给出了合理的解释.     

写入光偏振态对Ce:KNSBN晶体衍射特性的影响

采用非同时读出条件下晶体两波耦合实验装置,以单束光入射Ce:KNSBN光折变晶体,通过改变抽运光偏振方向和品体c轴的夹角φ.系统记录了不同φ角下的抽运光透射光强I',随时间的变化情况.实验结果表明,当φ≤30°时,基本没有光扇效应;实验研究了正交偏振光写入下Ce:KNSBN晶体的两波耦合动态过程,并与e光写入下两波耦合动态过程进行了比较,发现正交偏振光写入时光扇噪声得到了明显抑制,在相同的写入参量条件下光栅的衍射效率明显提高.     

Ce:KNSBN晶体两波耦合中的光扇效应

采用两波耦合非同时读出实验装置,测量了掺铈钾钠铌酸锶钡(Ce：KNSBN)晶体两波耦合过程中的信号光和抽运光非同时打开条件下两波耦合增益的时间变化规律,讨论了光扇的入射光强阈值及光扇效应对两波耦合动态过程的影响。结果表明：632.8 nm He-Ne激光在Ce：KNSBN晶体中写入体光栅时,光扇效应存在明显的写入光强阈值特性,当入射光强大于30mW／cm^2时才存在强烈的光扇效应。利用修正耦合波方程对Ce：KNSBN晶体中的两波耦合动态过程、增益随着信号光和抽运光打开时间间隔△t的变化进行了模拟计算,理论模拟结果与实验测量结果基本一致。     

偶氮类有机材料光致双折射的测量

研究了2种偶氮聚合物薄膜的光致双折射效应,并探讨了泵浦光偏振态和光强对光致双折射的影响.采用远离共振区的He-Ne光(633nm)作为探测光,用Ar+激光(488nm)作为泵浦光,通过测量相关参量得到了样品的光致双折射值.实验结果表明:改变泵浦光的偏振态可以控制光致双折射值和探测光的透过信号强度,在0°～45°范围内,泵浦光光强存在最佳值,此时偶氮薄膜实验样品具有最大的双折射值.     

甲基橙偶氮染料掺杂聚乙烯醇薄膜的光存储特性研究

研究了甲基橙(MO)偶氮染料掺杂聚乙烯醇(PVA)薄膜的光致双折射和全息光存储特性.利用YAG激光二倍频(532nm)作为写入光,He-Ne激光(632.8nm)作为读出光,考察了不同染料浓度薄膜的光致双折射,探讨了光致双折射和泵浦光功率的关系,并实现了全息光存储.阐明了MO/PVA光存储的物理机制.     

+1/-1相位掩模板和532nm激光下低损耗As_2S_3硫系光纤布喇格光栅的制备

采用改进型Sagnac干涉光栅写入系统,利用532nm准带隙光曝光源和带+1/-1衍射级的相位掩模板,在两种不同直径的低损耗As_2S_3硫系玻璃光纤上刻写布喇格光栅,并研究曝光期间光栅的动态特性.实验表明,As_2S_3光纤布喇格光栅透射峰值随光纤直径的减小而增强;在曝光过程中,布喇格波长先是较快地向短波长方向移动,随着曝光时间的延长,布喇格波长缓慢地向长波长方向回复.曝光时间为800~1 000s时,在包层直径为140μm的As_2S_3光纤上获得质量良好的布喇格光栅光谱,其透射峰值可达-2.6dB,带宽为0.37nm.对As_2S_3硫系光纤纤芯的光敏性分析结果表明,折射率调制幅度和平均折射率变化随曝光时间分别可达到10-4和10-3数量级.     

可擦除光存储教学实验的开设

研究了在聚甲基丙稀酸甲脂（PMMA）中掺杂羚羟基亚甲基苯胺N-salicylideneaniline(SA)样品的可擦除光存储特性，依据相干光调制光强分布诱导光异构形成相位光栅和光异构产生压力梯度引起质量输运形成表面光栅机理，分析了两光栅的相位关系，合理解释了写入过程和擦除过程中衍射信号强度随时间的变化关系，通过阐述上述复杂的分析过程，培养和提高学生分析问题与解决问题的能力。     

超短脉冲激光光束在一维反射型体全息光栅中的衍射

基于Kogelnik的耦合波理论,研究了在色散效应的影响下,超短脉冲激光光束在反射型体全息光栅中衍射的性质.研究给出了衍射光及透射光在频谱域及时间域的振幅及强度分布、光栅的光谱宽度及衍射效率随光栅参量及入射条件的变化.数值研究的结果表明,在光栅记录介质色散效应的影响下,衍射光束的光谱宽度减小,脉冲展宽,衍射效率降低.通过适当的选取光栅参量及入射条件,可以控制衍射和透射光束的频谱和时间强度分布,得到满意的衍射和透射光束的带宽和波形,从而可以将其应用于脉冲整形等技术中.     

不同生色团对聚合物薄膜全光开关效应的影响

在聚甲基丙烯酸甲酯(PMMA)中掺人不同的偶氮染料并制成薄膜样品,以调制的线偏振Ar^ 激光(514nrn,CW)作为控制光,He-Ne激光(632．8nm,CW)为信号光,研究了样品的光致双折射效应及全光开关效应。通过对样品的响应特性和全光开关效应进行比较,发现电子推拉势较强的生色团分子在控制光作用下,可以产生较大的光致双折射效应,但光响应速度较慢,其光致双折射效应以光致异构取向为主要机制;而对于具有较弱电子推拉势的生色团分子,其光致双折射效应则主要来自光致异构烧孔机制,虽然其光致双折射效应小,但光响应速度快。     

不同基体刚性偶氮化合物光致光学各向异性及其唯象模拟

在不同刚性的聚合物基体聚甲基丙烯酸甲酯（PMMA）、聚乙烯咔唑（PVK）和聚苯乙烯（PS）薄膜基体中掺入相同质量分数（均为0．003）的分散红13（DRl3）偶氮染料。以线偏振连续Ar^＋激光（514nm）作为控制光,连续He-Ne激光（632．8nm）作为信号光考察了具有相同厚度的三种样品在相同控制光功率（15mW）下的光致双折射效应。实验发现刚性较大的聚乙烯咔唑基体样品的双折射效应最小,刚性最小的聚苯乙烯基体样品的双折射效应最大。在偶氮生色团光致异构的四能级模型基础上,建立一新的唯象的模型。在模型中引入描述聚合物基体刚性的参量s,通过数值计算描述了不同基体刚性参量s对偶氮生色团光致异构取向的影响。计算结果表明,基体的刚性越大,样品的光致双折射效应越小,定性地解释了实验现象。     

Photoinduced Birefringence in Poly(Methyl Methacrylate) Polymeric Thin Films Doped with Di-Azo Sudan G

Photoinduced birefringence in poly(methyl methacrylate) (PMMA), polymeric thin films doped with di-azo Sudan G was investigated. A pump-probe method was used to study the dynamic behavior of the birefringence. The mechanism for the inducement of birefringence is discussed in terms of the photoisomerization of the di-azo Sudan G molecules. The results showed that the dynamic evolution of the photoinduced birefringence was such that the average birefringence increased, saturated, and then decreased with respect to the laser pump intensity. Also, an exponential-like relationship was observed between both the saturation and the isotropic states of the averaged transmitted probe beam (expressing the residual anisotropy) and the birefringence on one hand, and the intensity amplitudes of the pumping powers on the other hand.     

All-optical switching effect based on azodye-doped polymer thin films

A simple all-optical switch based on photoinduced birefringence effect is demonstrated in azo dye (DR1) doped polymer (PMMA) thin films. The all-optical switching effect has been studied at different control beam power and different temperatures of the sample. With a control power of 30.7 mW and at 56 ℃, the response time of the switching is less than 5 ms, and the depth of the modulation reaches 80%.     

Large inverse relaxation of photoinduced birefringence in an azobenzene-containing ionic self-assembly complex

Photoinduced anisotropy and polarization holographic recording were investigated in an azobenzene-containing ionic self-assembly complex. The complex film was found to possess large photoinduced dichroism (D～0.36) and photoinduced birefringence (Δn～10^?2). A noteworthy observation was that the photoinduced birefringence did not show any decay, but strongly increased after switching off the pump light at room temperature. The diffracted signals of the polarization holographic gratings, written by two orthogonally linear and circular polarized beams respectively, exhibited similar inverse relaxation behavior as the photoinduced birefringence after switching off the writing lights. A discussion about the mechanism accounting for the abnormal relaxation process of photoinduced birefringence is presented.     

Improvement of all-optical switching effect based on azobenzene-containing polymer films

A method for improving the quality of all-optical switching is presented. Pumping poly(methyl methacrylate) (PMMA) films doped with azobenzene chromophore Disperse Red 1 (DR1) with two beams (a linearly and a circularly polarized), all-optical switching effects with very low background and high stability are demonstrated. High frequency switching, which is hard to be realized under pump of a single beam, is obtained. The circularly polarized pump beam can erase the photoinduced birefringence and quicken the relaxation process, thus lowering the background and improving the stability and the extinction ratio of the switching signal. PACS 42.70.Jk; 42.25.Lc; 82.30.Qt; 78.20.Fm; 77.80.Fm     

新型含偶氮侧链聚合物中光致各向异性及偏振全息记录

研究了偶氮侧链聚合物中光致各向异性和偏振全息, 确认在这种聚合物中分析光致各向异性动力学过程时, 必须考虑光漂白效应的影响, 测量表明该聚合物具有大的光致双折射（Δｎ ＝７．８×１０－ ３）, 并在其中记录了高衍射效率（η＝ １９．３％ ）的偏振全息图     

Increase of photoinduced birefringence in a new type of anisotropic nanocomposite: azopolymer doped with ZnO nanoparticles

We report a significant increase of about 50% of the photoinduced birefringence in nanocomposite films of azopolymers doped with ZnO nanoparticles compared with samples made from nondoped azopolymers. This increase is most pronounced at small concentrations of the nanoparticles of 0.5% and for the amorphous polymers used in our study. We observe also an improvement of the response time of more than 25% in some of the polymers, which allows for faster and more effective polarization optical recording.