Enhanced Photorefractivity of Poly(N‐vinylcarbazole)‐Based Composites through Electric‐Field Treatments and Ionic Liquid Doping

It is shown that the photorefractive (PR) performance of polymer composites based on poly(N‐vinylcarbazole) can be improved when samples are subjected to an electric field for a certain time, i.e. conditioned, previous to the PR characterization. It is also found that for conditioned samples the addition of an organic ionic liquid to the PR composition allows to obtain PR effect without the need of using a sensitizer. The typical electric field treatment time at room temperature and at a field of 20 V µm^?1 is 20 min. This procedure leads to a decrease of dark conductivity and an increase of photoconductivity, and consequently an increase of conductivity contrast. This results in higher PR two‐beam‐coupling gain coefficients and shorter response times, particularly at low fields. Dependencies of the process dynamics on impurities, applied field strength, temperature and the presence of an organic ionic liquid are examined in detail. It is remarkable the significant increase of the PR gain coefficients, and more drastically of the net gain coefficients, observed at low fields (<55 V µm^?1), when an ionic organic liquid such as benzalkonium chloride is added to unsensitized conditioned PR composites. These findings open a new route to improve the PR performance, not only of PVK‐based composites, but also of other types of organic materials, the main advantage being that no sensitizer is needed.     

Photorefractivity and transmission‐type holograms of a poly(N‐vinylcarbazole)‐based composite with N‐4‐nitrophenyl‐(l)‐prolinol as chromophore

The photorefractivity of a poly(N‐vinylcarbazole)/2,4,7‐trinitro‐9‐fluorenone/N‐4‐nitrophenyl‐(l)‐prolinol/N‐ethylcarbazole composite was investigated by two‐beam coupling and degenerate four‐wave mixing experiments. The composite in a weight ratio 35 : 1 : 50 : 15 exhibited a 22% steady‐state diffraction efficiency and 70 cm⁻¹ two‐beam coupling coefficient at the applied external field of 55 V/μm. Zero applied field transmission‐type holograms were observed in the photorefractive sample as well as the spin‐coated thin film. The dynamic decay of diffraction light indicated that there existed two contributors with different phase‐shift, and the slow decay time can be as long as several h under continuous illumination by the readout beam. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 447–451, 2000     

有机-无机纳米复合光折变材料的合成研究

有机-无机纳米复合光折变材料具有优异的光折变性能和重要的应用前景。以PVK基掺杂型光折变体系为基础，制备了一种新型的光折变材料，并对其进行了表征。合成了低玻璃化温度的非线性分子DMNPAT，通过增加烷氧基的长度降低光折变体系玻璃化温度；采用化学复合方法在电荷传输体PVK上复合GdS半导体纳米粒子作为光敏剂，提高体系的光导性，可望具有较好的光折变性能。     

载氢光纤光折变的测量研究

报道了用光纤马赫－陈德尔干涉仪测量载氢通信光纤在１９３ｕｍＡｒＦ准分子紫外激光辐照下光致折射率变化的过程，为进一步制作光纤光栅器件和分析光折变机理提供了有用的实验数据。     

Evaluation of InP:Fe parameters by measurement of two wave mixing photorefractive and absorptive gain

In this paper, we present two-wave mixing absorption gain measurements in InP:Fe in the 960–1035 nm wavelength range. The measured absorption gain is shown to be positive for long wavelength but changes sign for shorter wavelength. By simultaneously measuring the photorefractive gain and the absorption gain, we deduce the values of the photo-ionization cross sections related to the iron deep level trap. Finally, the study of the temperature dependence of the absorption gain allows us to evaluate a temperature shift of the iron level with respect to the conduction band of −4×10⁻⁴ eV/K.     

A Brief Review of Carbazole-Based Photorefractive Liquid Crystalline Materials

Liquid crystals are commonplace in technological devices, such as watch and computer displays and temperature and pressure monitors. Such materials are central to our technological lifestyles. Classically, liquid crystalline materials are based on a structural motif which could be classed as rod-like (e.g. biphenyl derivatives) and in more recent times as disc-like (e.g. triphenylene derivatives). The rod-like materials are very attractive in terms of their chemical stability and their response to electric fields, both of which are a prerequisite for display devices, whereas disc-like materials show promise as one-dimensional conducting materials. Increasing scientific and technological requirements mean that new materials are continually sought to surpass the liquid crystalline materials which are presently known. Carbazole derivatives are well-known interesting natural products. Several methods have been developed and reported in the literature for the synthesis of carbazole derivatives. There are several review articles published on the photorefractive properties of carbazole-based materials. Chemical modification of the carbazole moiety to create a new class of discotic, calamitic and banana-shaped liquid crystalline materials, which will have novel and enhanced photorefractive properties over the amorphous carbazole derivatives, will be discussed in this mini review.     

σ-π共轭聚合物光折变特征研究

合成一种σ π共轭聚合物 poly(disilanylene 2 ,2′ bipyridine 5 ,5′ diyl)ruthenium (PDSBpy Ru) ,双光束耦合(2BC)、四波混频 (DFWM)及场致双折射实验等证明了该有机物的光导及光折变特性。由于铷化合物的金属与配位体间 (MLCT)电荷转移特性 ,使得该聚合物的光折变特性得以增强。实验测得双光束耦合增益系数为 30cm-1 ,四波混频实验测得光栅衍射率约为 1 0 %。     

KNbO3：Fe的红外光折变效应

利用1.15μm He-Ne激光对光折变晶体KNbO_3:Fe的二波耦合实验测量,得到二波耦合增益系数为1.4cm~(-1),频率响应时间为5ms.在红外波段的初步实验结果与可见波段的规律相符.     

KNbO3：Fe环形腔被动相位共轭器

介绍有附加反射镜组成的KNbO_3:Fe环形腔自泵相位共轭器,实验演示了相位共轭光建立过程中各光束间的能量转移现象,并测得自泵相位共轭反射率R随入射角α、环形腔光束夹角2θ和入射光强I_4的依赖关系,在最佳条件α=23°和2θ=20°时,测得最大的相位共轭反射率R=36%。