Chiral mirror and optical resonator designs for circularly polarized light: suppression of cross-polarized reflectances and transmittances

A left-handed chiral sculptured thin film (STF) that reflects strongly at the wavelength of the circular Bragg resonance tends to partially convert the handedness of incident LCP (left-circularly-polarized) light to RCP (right-circularly-polarized). We show that the cross-polarized component of the reflected RCP beam can be eliminated by interference with an additional RCP beam that is reflected at the interface of an isotropic cover and an AR (antireflecting) layer. For best results the refractive index and thickness of the AR layer need to accommodate a phase change on reflection that occurs at the chiral film. Effective suppression of the reflectances R_RR, R_RL, R_LR and the transmittances T_RL, T_LR can be achieved by sandwiching the chiral reflector between such amplitude and phase-matched AR coatings. Co-polarized chiral reflectors of this type may form efficient handed optical resonators. For LCP light the optical properties of such a handed resonator are formally the same as the properties of the isotropic passive or active Fabry–Perot resonators, but the handed resonator is transparent to RCP light.     

Nd:Ca4ReO(BO3)3(Re=Gd,Y)晶体最佳激光、最佳倍频及最佳自倍频方向的确定

介绍了Nd:Ca4ReO(BO3)3(Re=Gd,Y)晶体最佳激光方向、最佳倍频方向的确定.综合考虑激光受激发射截面、抽运光吸收系数、有效非线性系数的各向异性,分析了自倍频性质的空间分布,并就此确定出最佳自倍频方向 关键词： Nd:Ca4ReO(BO3)3(Re=Gd Y)晶体 激光发射 倍频 自倍频     

Phase diagrams and dielectric studies of binary mixtures exhibiting intermediate nematic and induced smectic phases

Investigations on the phase diagrams of two bi-component mixtures of liquid crystals are presented. Whereas in one of the bi-component systems, smectic A (SmA) phase is seen to be induced, in the other case the so-called nematic “island” has been observed. The dielectric properties of magnetically oriented sample forming nematic phase and induced smectic phase in one of the mixtures, and a nematic “island” and SmA phase in the other mixture, were measured in the frequency range from 1?Hz to 10?MHz at different temperatures. The transition temperatures obtained from the polarizing microscope and differential scanning calorimeter measurements agree well with the dielectric relaxation data.     

Smectic polymorphism of 4-decyloxybenzylidene- 4′-alkyloxyanilines and their mixtures with polar standards of mesophases

This article describes liquid crystalline properties of the homologous series of 4-decyloxybenzylidene-4′-alkyloxyanilines. Based on the polarization microscopy (POM and TOA methods) and the calorimetric (DSC) measurements a rich polymorphism has been detected. Investigated compounds exhibit nematic, smectic A, smectic C, smectic B, smectic I and G (smectic G) mesophases with their characteristic configurations. The presence of these mesophases was confirmed by the miscibility method, using 4-heptyloxybenxylidene-4′-pentylaniline as a mesophase reference. Nine other smectic standards with different polarity have been applied in order to investigate their influence on the mesophase stability.     

Optical spectra of triglycine sulfate crystals in the range of 7–33 eV and its changes at phase transition

Pseudo-dielectric functions ?ε₁(E)? and ?ε₂(E)? of triglycine sulfate (TGS) crystal have been obtained in the range of 7–33 eV for different temperatures close to ferroelectric phase transition by spectral ellipsometry using the synchrotron radiation source BESSY II. These dielectric functions ε₁(E) and ε₂(E) have also been calculated from first principles using CASTEP CAmbridge Serial Total Energy Package code together with the band structure and density of electronic states of the crystal. Experimental and theoretical dielectric functions agree satisfactorily. A characteristic decrease of temperature dependences of the dielectric losses tgδ(T) and related values just below the phase transition temperature T _c have been found and discussed.     

Undulation textures at the phase transitions of some alkyloxybenzoic acids

We observed undulated smectic textures for some compounds of the 4,n-alkyloxybenzoic (nOBAC) acid series, at transitions between the smectic and the isotropic phase and between the smectic and nematic phase. Studied compounds were 12OBAC, 16OBAC and binary mixtures of 12- and 16OBAC. The undulations are dressing a usual Schlieren texture. An interesting fingerprint pattern is observed at the smectic-nematic in the case of the binary mixture, approximately 1 : 1 in weight.     

Thermal expansion of Sn2P2S6 crystals

We present the results for thermal expansion coefficients of Sn₂P₂S₆ crystals determined both in the crystallographic system and the system based on eigenvectors of thermal expansion tensor. Peculiarities of temperature evolution of the indicative surface of thermal expansion tensor for Sn₂P₂S₆ are discussed, including the region of their ferroelectric phase transition.     

Evidence of pressure dependence tricritical point at the nematic–smectic-A transition

We examine the effect of pressure on the nematic to smectic-A N–SmA) transition within the Landau phenomenological theory. The influence of pressure on the N–SmA transition is discussed by varying the coupling between the orientational and translational order parameters. The possibility of the tricritical point at the N–SmA transition is discussed in a phenomenological way. The theoretical predictions are found to be in good qualitative agreement with experimental results.     

二维非极性晶体中声学形变势表面磁极化子

本文研究磁场中二维非极性晶体通过形变势与声学声子强、弱耦合的表面极化子的性质。采用线性组合算符和拉格朗日乘子法导出表面磁极化子的基态能量。讨论了表面磁极化子的振动频率、基态能量和有效质量与磁场的关系。     

基于缺陷光子晶体结构的GaN基发光二极管光提取效率的有关研究

现有的研究表明,利用光子晶体可以有效提高发光二极管的光提取效率.由于在制造时光子晶体中可能会存在缺陷和错位,本文基于时域有限差分法对光子晶体中的缺陷和错位对发光二极管发光效率的影响进行了研究.数值仿真结果表明,光子晶体中少量缺陷或者微小错位并不会降低发光二极管的光提取效率,其中某些缺陷反而能增强光子晶体发光二极管的光提取效率.本文对其物理机理给出了详细的理论分析,并设计了一种具有缺陷的光于晶体,在未刻蚀到有源层(离有源层20 nm)的情况下,其光提取效率达到了完美光子晶体的1.6倍.通过对这种缺陷光子晶体的空间频谱分析可知,可以通过设计具有特殊空间频谱分布的光子晶体来提高发光二极管的发光效率,这对设计高光提取效率的光子晶体结构和制造高效率的发光二极管有指导意义.