Photoinduced changes in optical and contact properties of chalcogenide glasses

Photoinduced changes in optical and contact properties in thin films of glasses of As-Se and As-S systems are studied experimentally. The changes detected in the optical constants and parameters of the potential barrier at the interface between a metal and a chalcogenide vitreous semiconductor are explained by the rearrangement of the glass host under the action of radiation.     

Compositional dependences of average positron lifetime in binary As-S/Se glasses

Compositional dependence of average positron lifetime is studied systematically in typical representatives of binary As-S and As-Se glasses. This dependence is shown to be in opposite with molar volume evolution. The origin of this anomaly is discussed in terms of bond free solid angle concept applied to different types of structurally-intrinsic nanovoids in a glass.     

P-T diagram in the As-S system

Abstract

Chalcogenide glasses in the system As-S are candidates for very low loss fiber-optic materials. In order to modulate physical properties of such glassese by wellaimed pressure variation the knowledge of the P-T diagram is a precondition. Therefore the aim of this investigation was to cheque the energy-dispersive X-ray diffraction method for low symmetry materials like Realgar (AsS) in order to elaborate P-T diagrams in a time reducing technique.     

Low-frequency inelastic light scattering from As-S glasses

Raman scattering from As-S glasses were observed in the low-frequency region, from 5 to 60 cm^?1. The spectral features depend on the quenching and annealing conditions as well as on the temperature and the composition. The spectrum was explained in terms of the vibration of the layer-like clusters coupled with each other through van der Waals forces.     

A Raman study of lithium fluoride containing fast ionic conducting glasses

The role of fluorine in the structure of fluoro-borate fast ionic conducting glasses has been studied by Raman spectroscopy. It is shown that addition of LiF results in important structural changes, compared to binary glasses with the same O/B ratio. The Raman results are consistent with the participation of fluorine in the network. Careful control of the O/B ratio is required in order to detect the alkali fluoride-induced structural changes by Raman spectroscopy.     

紫外可见吸收光谱检测pH值对光聚合脂质体的影响

利用紫外可见吸收光谱法考察脂质溶液pH值对光聚合脂质体的影响.通过水浴超声法制备光聚合脂质体,然后以脂质体的光学特性作为主要指标,利用光谱扫描测量各体系在640nm、540nm处的吸光值,利用比色响应值(CR)来对不同pH值下光聚合脂质体的颜色变化进行定量分析.结果表明,随着pH值的增大,光聚合脂质体溶液颜色由蓝色逐渐变成深红色.     

Signatures of structural recovery in colloidal glasses

Colloids near the glass concentration are often taken as models for molecular glasses. Yet, an important aspect of the dynamics of molecular glasses, structural recovery, has not been elucidated in colloids. We take advantage of a thermosensitive colloidal suspension to study the structural recovery after concentration jumps by using diffusing wave spectroscopy. The three classical aging signatures observed in molecular glasses are studied and the results are compared with those typical of molecular glasses. For the intrinsic isotherms, unlike molecular glasses, the colloid shows huge changes in relaxation time at equilibrium while the times required to reach the equilibrium state are nearly constant. For asymmetry of approach, we find a similar nonlinearity to that observed in the molecular glasses. For the memory experiment, while a memory effect is seen, the response is qualitatively different from that in molecular glasses.     

A note on the Raman spectra and structure of Asx S100−x (x ⩾ 40) glasses

A recent paper in this journal by Slade and Zallen states that the present authors have suggested that actual microcrystals of β-As₄S₄ are present in vapour-deposited films of As₂ S₃. This is a mistaken interpretation of our previous work and in correcting the record we make some additional observations on the Raman spectra and structure of glasses in the As-S system. It is concluded that the Raman data is inconclusive on the existence, or otherwise, of phase-separated crystals.     

Laser heterodyne measurements of photo-induced refractive-index changes in amorphous As-S films

A differential-type heterodyne interferometer has been successfully utilized for studying the refractive-index changes in As-S films under illumination. The measuring system can detect phase changes down to 1° in angle in accuracy and sensitivity. It is confirmed that illumination of the films involves two distinct factors: a thermal and an optical one. The index changes are caused only by the optical effect. The time-dependent characteristics of the index changes are explained to be closely related to the photo-darkening effect.     

Density and structural changes of silicate glasses under high pressure

ABSTRACT

Density and structural changes of matter in their liquid or amorphous form, such as silicates melts, molecular fluids, or glasses, are of extreme importance to model the interior of planetary bodies. However, measuring the evolution of amorphous materials under extreme conditions of pressure and temperature remains challenging mainly because of the sample dimensions and the weak interaction with X-ray probes. This contribution highlights recent developments to measure the density of amorphous material, mainly silicate glasses made of light elements, to high pressure conditions. In particular, the X-ray absorption method at synchrotron sources is discussed as a new opportunity for high pressure experiments on glasses, fluids, and melts. Recent achievements using X-ray Raman scattering spectroscopy to obtain data on the local electronic environment of the main constituents of silicate glasses at high pressure are also presented. Finally, perspectives of these recent developments are discussed as well as their potential for high pressure research in the next years.     

Photopolymerization-Induced Two-Beam Coupling and Light-Induced Scattering in Polymethyl Methacrylate

Light amplification due to two-beam coupling is realized in doped polymethyl methacrylate （PMMA） glasses. A coupling gain as large as 14 cm^-1 is obtained. The dynamic behaviour of absorption and light-induced scattering due to the process of photopolymerization are also studied. The results show that the amplification and its dynamic process enable possible applications of PMMA in optical devices.     

Parallel two-photon photopolymerization of microgear patterns

We report parallel two-photon photopolymerization of microgear patterns by exposing a photoresist to holographically generated optical vortices. The optical vortices are created by imparting a helical pitch onto the incident light using a programmable lithographic phase mask realized with a computer addressable phase-only spatial light modulator. By varying the phase levels of the spatial light modulator, the truncated helical phase of an optical vortex results in output intensity patterns that typifies that of microgears instead of perfect doughnut beams. Our experiments and simulations are in good agreement implying a more efficient and highly parallel two-photon photopolymerization scheme that can be subsequently used for non-scanning fabrication of microgears.     

A phototermal experiment interpreted as evidence of electron-hole self-ordering in As-S chalcogenide glasses

The photodeflection method has been applied to detect optically induced changes of the refractive index due to self-organization of electrons and holes, trapped in the disordered structure of a chalcogenide glass of the As-S type.     

基于液晶光阀的防眩目眼镜

基于常开型液晶光阀的电光特性设计了一种司机夜间行车时佩戴的液晶眼镜．液晶眼镜能够主动根据外界光强变化改变自身的透射率,从而使透射光强趋于稳定值．实验结果表明液晶眼镜能有效防止对面车灯引起的眩目, 同时不影响司机对路面的观察．     

Concentration dependence of radiation-induced changes in the optical properties of Ge<Subscript>x</Subscript>As<Subscript>40−<Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>60</Subscript> films

Radiation-induced changes in the optical properties of chalcogenide glasses in the Ge-As-S system are investigated as a function of the concentration. Theoretical calculations are performed with due regard for possible constraints on the range of variation in the number of homobonds and heterobonds upon their switching in the structural network of chalcogenide glasses. The experimental data are obtained upon irradiation of Ge_xAs_40?xS₆₀ thin films with fast electrons (6 MeV). The possible mechanism of structural transformations responsible for the specific features in the concentration dependence of the change in the band gap of chalcogenide glasses is discussed.     

The studies of structural aspects of the cluster formation in silicate glasses doped with cerium and titanium oxides by small-angle neutron scattering

The structural aspects of the formation of Ti-Ce-O nanoclusters in silicate glasses doped with oxides TiO₂ and CeO₂ have been studied by means of small-angle neutron scattering. It has been obtained that, in such glasses, complex oxide nanoclusters with sizes of 300–380 Å are formed; their average size increases and the fractal dimension is changed as the concentration of the initial oxides increases. Correlation between the structural characteristics of the nanoclusters and the optical properties of the doped silicate glasses is discussed.     

Photopolymers — Holographic investigations,mechanism of recording and applications

The holographic characteristics of a broad class of photopolymerization systems of the acryl type — metal (Ba, Pb, Ca, Sr) acrylates and acrylamide — are investigated. The conditions — composition, recording light intensity and spatial frequency — for self-fixing real-time recording are defined. Holographic techniques are employed to determine some basic characteristics of the photopolymerization reactions — order of the photochemical reaction and diffusion coefficients of the monomers used. Experiments are carried out proving the suitability of the investigated photopolymerization systems for optical correlation processing.     

TiO2对磷酸钙玻璃结构影响的Raman光谱研究

利用Raman光谱、X射线衍射(XRD)和热分析(DSC)技术研究了包容TiO2的磷酸钙玻璃的结构特点.结果表明,TiO2添加量小于3 mol%时,与磷酸钙形成均质玻璃.添加量为6～12 mol%时,玻璃基体中生成了Ca2P2O7和CaTi4(PO4)6品相.随着TiO2的加入,玻璃体系中发生了偏磷酸盐向焦磷酸盐和正磷酸盐的结构转变.TiO2添加量小于3 mol%时,加入TiO2增强了玻璃结构的内聚力,使得玻璃转变温度逐渐提高,玻璃的热稳定性增强.     

Dynamic Light Diffraction by Holographic Gratings in Photopolymeric Materials

A theoretical model of light diffraction by tilted holographic gratings in photopolymeric materials in the nonstationary regime of reading, which describes the dynamic process of optical hologram amplification with allowance for the photopolymerization and diffusion mechanisms of recording, is developed. For the given model, the dynamics of the diffraction efficiency and selective properties of hologram reading are modeled numerically when Bragg's conditions are satisfied and violated. It is demonstrated that the diffraction characteristics of tilted holograms are spatially noninvariant for the reading beam direction. The optimal conditions of reading of tilted holograms are established.     

Short-range order changes induced by heat treatment in yttrium-aluminosilicate glasses

Short-range order and local atomic configuration in yttrium-aluminosilicate glasses doped with gadolinium were studied by infrared (IR) spectroscopy, ²⁷Al magic-angle-spinning nuclear magnetic resonance (MAS-NMR) and Gd³⁺ electron spin resonance (EPR) on as-prepared and heat-treated samples.A small amount of yttrium was replaced by gadolinium in the host glass because Y³⁺ and Gd³⁺ cations are quite similar and gadolinium ions can be used as structural sensor in electron paramagnetic resonance measurements. The results evidence weak changes in the structure of as-prepared glasses with respect to the coordination of aluminium atoms produced by gadolinium doping (0.2 and 0.5 mol%). New IR bands recorded from heat-treated samples are associated with stretching modes of hexacoordinated aluminium in AlO₆ octahedra. The effect of the heat treatment on aluminium environment is estimated by analysing the relative intensity of the component lines of simulated ²⁷Al MAS-NMR spectra. High-coordinated AlO_n species were identified in all samples. EPR results evidence the increase of the number of gadolinium sites with weak crystal field as effect of the structural relaxation.