Analysis of Internal Conical Refraction Using Ray Tracing Formulas for the Biaxial Crystal

Internal or external conical refractions are strange optical phenomena appearing in biaxial crystal. In this paper the analysis of internal conical refraction is derived using the ray tracing formulas for the biaxial crystals, after explaining the theory of the ray tracing for the biaxial or uniaxial crystals. The double rings of conical refraction are also investigated; these are affected by the polarization state or angular intensity distributions of the incident light beam causing conical refraction.     

Dispersionless polaritons at symmetrically oriented surfaces of biaxial crystals

A set of dispersion relations is derived for surface polaritons in optically biaxial crystals at the surfaces parallel to the symmetry planes of the permittivity tensor ?. The domains of existence, as well as the sectors of the propagation directions of dispersionless surface polaritons which arise at positive components of the tensor ?, are analyzed. Three nonoverlapping domains of the dielectric-anisotropy parameters where dispersionless polaritons can exist are found for weakly anisotropic crystals. In each of these domains, polaritons exist at two different mutually orthogonal surfaces of the crystal. In optically biaxial crystals, in contrast to optically uniaxial media, polaritons arise not only in positive but also in negative crystals. The evolution of the optical-axis configuration is traced as the anisotropy parameters vary in the domains of existence of polaritons.     

Calculation of nonlinear optical polarization and phase matching in biaxial crystals

We present a general, analytical formula for the calculation of the unit vectors of the direction of vibration of the electric field strength in biaxial crystals. By means of this formula it is possible to calculate the effective nonlinearity for second-order nonlinear optical frequency conversion processes in biaxial crystals. For two highly efficient nonlinear optical crystals we have calculated the effective nonlinear susceptibility and walk-off angles. The results have been compared with numerical as well as experimental data of previous papers.     

Effective-Field Theory on High Spin Systems with Biaxial Crystal Field

Based on the effective-field theory with self-spin correlations and the differential operator technique,physical properties of the spin-2 system with biaxial crystal field on the simple cubic, body-centered cubic, as well as faced-centered lattice have been studied. The influences of the external longitudinal magnetic field on the magnetization,internal energy, specific heat, and susceptibility have been discussed in detail. The phenomenon that the magnetization in the ground state shows quantum effects produced by the biaxial transverse crystal field has been found.     

Effective-Field Theory on High Spin Systems with Biaxial Crystal Field

Based on the effective-field theory with self-spin correlations and the differential operator technique, physical properties of the spin-2 system with biaxial crystal field on the simple cubic, body-centered cubic, as well as faced-centered lattice have been studied. The influences of the external longitudinal magnetic field on the magnetization, internal energy, specific heat, and susceptibility have been discussed in detail. The phenomenon that the magnetization in the ground state shows quantum effects produced by the biaxial transverse crystal field has been found.     

Growth and characterization of piezoelectric Sr3Ga2Ge4O14 crystals

Langasite (La3Ga5SiO14, LGS) and its isomorphs, have attracted much attention for their potential for surface acoustic wave (SAW) and bulk acoustic wave (BAW) applications. Among these homologous compounds, Sr3Ga2Ge4O14 (SGG) attracted our attention due to its superior piezoelectric properties and lower growth temperature. In this work, SGG single crystal has been grown successfully by the vertical Bridgman method with crucible-sealing technique. SGG wafers of 2 in. have been fabricated. The basic physical properties of SGG crystals were measured. The results demonstrate that piezoelectric and mechanical properties of SGG crystals are better than that of LGS crystal and it is expected to be a potential substrate material for SAW and BAW applications.     

双轴晶体和频效应的相位匹配拓朴分析

根据非中心对称双轴晶体中两束基频光与它们产生的二次谐波的折射率曲面的关系及相位匹配条件,分析了和频效应相位匹配曲面的特点,对正常双轴晶体得出了可实现的29种相位匹配曲面拓扑图和存在条件,15种非临界相位匹配类型、存在条件和偏振关系.并用这种理论分析了LAP晶体、KB_5晶体的和频性能.     

Probing the orientation of porphyrin oligomers in a liquid crystal solvent – a triplet state electron paramagnetic resonance study

ABSTRACT

Linear porphyrin oligomers have found various applications as synthetic molecular wires in the context of light harvesting, solar energy conversion and molecular electronics. In many of these applications a partial ordering of the molecules helps to improve the reaction efficiency or device performance. In this work we study the orientational properties of the building blocks of such porphyrin-based molecular wires, namely a porphyrin monomer and the corresponding butadiyne-bridged dimer. The porphyrins have been embedded in the nematic liquid crystal solvent 4-cyano-4'-pentylbiphenyl (5CB) and the anisotropic properties of their photogenerated triplet states were characterised by transient electron paramagnetic resonance (EPR) spectroscopy. When aligned in strong magnetic fields, the liquid crystal molecules impose their orientational anisotropy onto the solute guest molecules whose orientation-dependent magnetic properties can then be explored. The line shape analysis of the porphyrin triplet state EPR spectra – highly sensitive to small conformational changes – confirms the orientation of the zero-field-splitting (ZFS) tensors previously determined for these molecules by magnetophotoselection experiments. A biaxial distribution function is shown to be necessary to simulate the experimental EPR data. The biaxial behaviour, in conjunction with symmetry considerations, allows an unambiguous assignment of the three ZFS tensor axes to the molecular axes. From the determined orientational distributions of the porphyrins in 5CB, the biaxial order parameters for both molecules were calculated.     

Measurement of the biaxial properties of nineteenth century canvas primings using electronic speckle pattern interferometry

This paper reports on the use of electronic speckle pattern interferometry (ESPI) for the measurement of the biaxial tensile properties of English 19th century canvas primings and their constituent materials. Typically, such primings are comprised of a complex structure of layers, each with different mechanical properties. ESPI has been shown to be an effective technique for investigating complex composite structures and it is especially useful for understanding the behaviour of heterogeneous materials in which non-uniform strains can occur. The flexibility of canvas primings presents a more difficult application for both biaxial tensile testing and ESPI strain measurements. A series of experiments have been carried out to measure the Poisson's ratio of the three main constituents of a 19th Century priming as composites and of an original 19th century primed canvas. The samples have been uniaxially tensioned on a biaxial tensile tester designed specifically to investigate the mechanical properties of paintings on canvas. Measurements of deformation have made using a two-dimensional in-plane ESPI configuration. The results have shown that Poisson's ratio decreases as the constituents of a painting are built up. Preliminary tests on thermally aged and original primings suggest that for a painting without cracks it is the embrittled paint which determines the mechanical response of the painting at an relative humidity of 35–40%.     

A biaxial nematic gel phase in aqueous vanadium pentoxide suspensions

Aqueous suspensions of V₂O₅ ribbons are one of the very few examples of mineral liquid crystals. In the concentrated regime, we show that these ribbons organize in a biaxial nematic gel phase. A Couette shear cell was used to produce a well oriented sample for in situ synchrotron X-ray scattering studies. We observed two perpendicular anisotropic sections of reciprocal space, which proves the biaxial symmetry of the nematic order. The thermodynamic and flow properties of the biaxial nematic are well described by hard-core theories. We suggest the use of a shear geometry to produce and investigate single domains of other biaxial nematics, reported but still questioned in the literature. Received 26 May 1999     

Rufigallol-based self-assembled supramolecular architectures

Discotic liquid crystals have been attracting growing interest not only because of the fundamental importance as model systems for the study of charge and energy transport but also due to their potential application in organic electronic devices. The 1,2,3,5,6,7-hexahydroxy-9,10-anthraquinone, commonly known as rufigallol, is one of the earliest systems reported to form columnar mesophases. Over the past 25 years, more than 100 discotic liquid crystals based on this core have been realized and studied for various physical properties. This review summarizes synthesis and thermal behaviour of all these materials. A brief summary of various physical studies on these materials has also been given.     

季氨盐对KDP晶体的光学特性影响

 生长了不同季氨盐掺杂浓度的KDP晶体，其锥光干涉实验显示了晶体的内应力引起的双折射和双轴晶特性较明显。透过率特性的实验结果表明，不同浓度的季氨盐对KDP晶体的光学均匀性有较大影响。报道了掺季氨盐0.001%的KDP晶体的异常光学透过率特性以及晶体具有三维变化的波片效应和旋光特性。     

Vacuum ultraviolet absorption of lithium fluoride crystals grown by zone melting

Optical properties are reported for LiF crystals obtained by zone melting from salts differing in synthesis and purity. The impurity distributions along the bars have been studied by chemical analysis and absorption spectrometry. The transparency is discussed as a function of the number of zone passes.     

On a group of two-parameter intramolecular distributions and their properties

A group of two-parameter intramolecular distributions for degenerate vibrations has been investigated. The distributions are of physical significance in calculating electronic transitions and have certain important properties which are formulated in terms of addition theorems.     

弛豫铁电单晶的研究进展—压电效应的起源研究

由于具有优异的压电性能,弛豫铁电单晶自上世纪90年代问世以来即成为了铁电压电领域研究的热点材料,并被认为是研发下一代高性能换能器、传感器等器件的重要压电材料。弛豫铁电单晶不但压电常数可达2500 pC/N,约为软性Pb(Zr,Ti)O3(PZT)陶瓷的5倍,而且其电致应变滞后也远小于软性PZT陶瓷。因此,弛豫铁电单晶高压电性能的产生机理一直是铁电压电领域的研究热点。本文主要介绍了弛豫铁电单晶材料在近些年的发展,从本征压电效应(晶格压电畸变)的角度归纳总结了弛豫铁电单晶高压电效应的产生机理,着重探讨了弛豫铁电单晶的重要特点—剪切压电效应。在本征效应的基础上,本文对弛豫铁电单晶压电效应与晶体组分、切向以及温度的关系进行了分析。需要指出的是,目前基于本征角度对弛豫铁电单晶高压电效应的分析仍处于定性的阶段,因而还不能完全排除一些可能导致弛豫铁电单晶高压电效应的非本征物理机制。     

The influence of solar radiations to the physical and structural properties of CR-39

Long chain polymers owe many of their properties to the structural arrangements of their molecules and are extensively used for many industrial and applied sciences. One of such application is their perspective use in the field of solid-state nuclear track detectors. However they are profoundly influenced by low LET radiations exposure and new structural arrangements may emerge. CR-39 is one of the most popular polymeric track detectors, however its aliphatic nature restricts its applications. Thus in the present investigations the damage densities produced by solar radiations to the polymer have been estimated by analyzing the structural, physical and etching properties of the polymer. The polymer is found to be highly sensitive towards solar radiations and great changes in physical and structural properties of polymer have been observed. The sensitivity of the polymer has been found to decrease by 83.40% during eight months.      

Absorption and luminescence spectra of KHo(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> and KEr(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> single crystals

The optical absorption and luminescence properties of potassium-holmium and potassium-erbium double tungstates have been studied. It is established that the potassium-holmium double tungstate belongs to a group of biaxial and pleochromic crystals. The emission and excitation spectra of the KHo(WO₄)₂ and KEr(WO₄)₂ single crystals were measured at room temperature.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 71, No. 6, pp. 810–814, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Photoconductivity, dielectric and thermal investigations of pure, benzophenone- and iodine-doped benzoyl glycine NLO single crystals

Physical properties such as photoconductivity, dielectric and thermal stability have been investigated for pure benzoyl glycine (BG) crystals. In addition to this, the influence of dopants (benzophenone and iodine) of these properties on BG crystals has been studied. Photoconductivity studies on pure BG, benzophenone-and iodine-doped BG revealed the positive photoconducting nature. The dielectric responses of the samples have been studied in the frequency range 100 Hz-500 KHz at room temperature and the results are discussed in detail. The thermogravimetric studies of pure and doped BG crystals indicate that the presence of dopants has slightly increased the decomposition temperature of pure BG samples, thereby enhancing thermal stability to the doped ones.     

Monte Carlo simulations of biaxial structure in thin hybrid nematic film based upon spatially anisotropic pair potential

Hybrid nematic films have been studied by Monte Carlo simulations using a lattice spin model, in which the pair potential is spatially anisotropic and dependent on elastic constants of liquid crystals. We confirm in the thin hybrid nematic film the existence of a biaxially nonbent structure and the structure transition from the biaxial to the bent-director structure, which is similar to the result obtained using the Lebwohl--Lasher model. However, the step-like director's profile, characteristic for the biaxial structure, is spatially asymmetric in the film because the pair potential leads to K₁ ≠ K₃. We estimate the upper cell thickness to be 69 spin layers, in which the biaxial structure can be found.