Rayleigh Scattering Losses in Soda Borosilicate Glasses

The present writers predicted that Rayleigh scattering losses in some soda borosilicate glasses would be less than in pure vitreous silica. The simple heuristic arguments that lead to this prediction and the scattering loss measurements which appear to confirm it are presented.     

Light Scattering and Spinodal Decomposition in Glasses

It is shown that the well-known anomalous Rayleigh scattering of phase-separated glasses, which can be accounted for by the assumption of nucleation of a new phase followed by diffusion-controlled growth, can also be qualitatively accounted for by the assumption that the phase separation is occurring within the spinodal region of the phase diagram; here there is no nucleation barrier to phase separation, only a diffusional barrier. A distinction between the two mechanisms in any actual system can be made only by the use of other experimental tools, such as electron microscopy. A quantitative theory of this process proposed by Cahn is examined; it is concluded that light scattering probably reveals only the later stages of the process, rather than the initial stages dealt with by Cahn's theory.     

Color and Light Scattering of Platinum in Some Lead Glasses

The coloration and light scattering of sodium lead silicate, borate, and phosphate glasses containing platinum, introduced as PtCl₄, have been studied. Under the normal atmosphere of a furnace heated by silicon carbide elements, the platinum is retained in the colloidal state in the sodium lead silicates and borates, producing gray glasses. In the phosphate glasses yellow to orange ionic colors as well as grays are produced. Lead oxide increases the stability of platinum ions in the phosphate glasses. Under strong oxidizing conditions, ionic platinum also can be obtained in the borate and silicate glasses. Tyndall scattering can be detected in what appear to be clear, colorless glasses. This light scattering has been observed in some glasses containing as little as 1 p.p.m. platinum.     

Specific Features of Light Scattering in Oxide Glasses in the Glass Transition Range

The change in the intensity of light scattering after temperature jumps in the glass transition range is investigated for phosphate and silicate glasses. It is demonstrated that the time dependence of the intensity exhibits a universal character, which manifest itself in the peak whose height and location depend on the thermal prehistory of the glass. The influence of the thermal prehistory on the height and the lifetime of the intensity peak is elucidated and the experimental conditions that correspond to the maximum scattering intensity and the longest duration of the transient process are determined for phosphate glass. It is revealed that the maximum height of the intensity peak nonmonotonically depends on the annealing temperature. An analysis of the results obtained shows that the mechanism of relaxation process of the low-temperature stabilization undergoes a crossover in the vicinity of the glass transition temperature. It is established that the observed variation in the intensity is characterized by the size effect. This makes it possible to assume that the intensity peak can be associated with the temperature gradient across the sample after the temperature jump.     

Rayleigh Scattering in Silica Glasses

Rayleigh-scattering properties in commercial silica glasses is clarified with relation to their fabrication methods. Fused silica and synthetic silica made by the flame hydrolysis of SiCl₄ (VAD) method exhibit similar magnitudes of scattering, regardless of fabrication method. Synthetic silica made by flame fusion of SiCl₄ exhibits ∼10% lower scattering than other silica glasses. The factors affecting scattering are evaluated based on refractive index dispersion and glass transition temperature (T_g). The results suggest that the difference in Rayleigh scattering is predominantly attributable to the difference in T_g , which is affected by impurities, such as OH ions.     

Phase Separation and Spatial Morphology in Sodium Silicate Glasses by AFM,Light Scattering and NMR

The morphological and structural properties of sodium silicate (Na₂O–SiO₂) glasses were analyzed using atomic force microscopy (AFM) and light scattering following thermal treatments. AFM observations indicated that the glass surface microstructure evolves during the phase separation mechanisms from continuous interpenetrating phases in the spinodal decomposition process to separated droplets embedded in a continuous matrix for the nucleation/growth one. Raman mapping gave evidence of a phase separation through the nucleation/growth process with formation of silica‐rich clusters characterized by higher polymerization degree as separate droplets. The variations in inhomogeneities versus temperature investigated by Brillouin are exponential for spinodal decomposition and linear in the case of nucleation/growth mechanism. Nuclear magnetic resonance spectroscopy was used to investigate the spatial distribution of the various Q_n species present in thermally treated glasses and allows determining fractal dimension between two and three.     

High-Temperature Integral Absorption in Glasses

The information published in various sources concerning IR absorption of certain glasses is summarized. The results are supplemented by the data of research carried out by the authors. It is proposed to use the integral absorption coefficient calculated for the considered glass compositions in solving the problems of radiation-conductive heat exchange. The resulting data bank will make it possible to predict the integral absorption of glasses containing certain transition elements, primarily, iron.     

Polarized Raman Scattering in Rare-Earth Fluoride Glasses

The polarized Raman spectra of rare-earth fluoride glasses based on BaF₂ and ThF₄, in combination with ZnF₂, YF₃, YbF₃, LuF₃, andlor AlF₃, are reported and compared with those of other heavy-metal fluoride glasses. The spectra of rare-earth fluoride glasses, especially those containing large amounts of AlF₃, have relatively broad and mostly depolarized features, suggesting that these glasses are more highly disordered than fluorozirconate and transition-metal fluoride glasses.     

高纯硫系玻璃和光纤的制备技术

高纯度硫系玻璃如As-A,As-Se和Ge-As-Se系统都是很有希望作为中红外低损耗的光纤材料，本文主要回顾了制备高纯度的硫系玻璃和光纤材料的一些问题，并对这些问题进行了讨论，最后举例说明了这种光纤的一些实际应用。     

Effect of Temperature Gradient on the Intensity of Light Scattering in Phosphate Glasses in the Glass Transition Range

A correlation between the peak of the intensity of light scattering and the temperature gradient arising across the sample after temperature jumps in the glass transition range is revealed from experimental data. Analysis of the experimental results shows that the peak of the intensity of light scattering is a quadratic function of the temperature gradient. The result obtained is in agreement with the predictions made from the theoretical analysis of the regularities observed in light scattering by nonuniformly heated liquids.     

Nonradiative Energy Losses and Radiation Trapping in Neodymium-Doped Phosphate Laser Glasses

Fluorescence radiation trapping and nonradiative energy losses from the Nd³⁺⁴F_3/2 state are reported for two widely used commercial phosphate laser glasses (LHG-8 and LG-770). The effects of hydroxyl-group, transition-metal (Cu, Fe, V, Co, Ni, Cr, Mn, and Pt), and rare-earth (Dy, Pr, Sm, and Ce) impurities on the ⁴F_3/2 nonradiative decay rate in these glasses are quantified. Nd concentration quenching effects are reported for doping levels ranging from about 0.5 × 10²⁰ to 8.0 × 10²⁰ ions/cm³. The results are analyzed using the Förster–Dexter theory for dipolar energy transfer. Quenching rates for transition-metal ions correlate with the magnitude of spectral overlap for Nd emission (donor) and the metal ion absorption (acceptor). The nonradiative decay rates due to hydroxyl groups follow Förster–Dexter theory except at low Nd-doping levels (≲2 × 10²⁰ ions/cm³) where the quenching rate becomes independent of the Nd concentration. The data suggest a possible correlation of OH sites with Nd ions in this doping region. The effects of radiation trapping on the fluorescence decay are reported as a function of sample size, shape, and doping level. The results agree well with the theory except for samples with small doping-length products; in these cases, multiple internal reflections from the sample surfaces enhance the trapping effect.     

显色工艺对纳米CdSexS1-x微晶玻璃光吸收曲线性能的影响

采用不同的热处理显色工艺对掺杂Se和CdS着色剂的硼硅酸盐玻璃进行热处理,制备出一系列的纳米硒硫化镉颜色玻璃,研究了热处理显色工艺对玻璃光透过性能的影响。结果表明,玻璃的截止吸收波长位置取决于热处理条件;采用低温长时间热处理工艺,使所制备的玻璃具有较高的光透过率和完整的吸收边界。微观结构分析表明,热处理后玻璃中出现的纳米微晶等结构变化是导致玻璃着色、出现光截止吸收的根本原因。     

Refractive Index Dispersion of Sodium Magnesium Silicate Glasses for Ultralow-Loss Fibers

The refractive index dispersion and infrared (IR) reflection spectra of soda magnesium silicate glasses with low Rayleigh scattering were measured to evaluate their potential for use in fabricating ultralow-loss fibers. The zero-material dispersion wavelength (λ₀) was found to be around 1.5 μm, which is one of the key wavelengths in the present telecommunication system. The compositional dependence of λ₀ was found to relate to the population of nonbridging oxygen. Since the oscillation strength and frequency of the Si—O stretching vibrations of the glasses were found to be smaller than those of silica glass, their IR absorption loss was considered to be less than that of silica glass. The minimum loss due to the intrinsic factors, Rayleigh scattering and IR absorption, was estimated to be 0.06 dB/km at 1.6μm.     

远红外Ge-Te-Se硫系玻璃与光纤(英文)

采用传统的熔融–淬冷法制备了系列GexTe65Se(35–x)(x=20,22,23,24;摩尔分数,x%)Te基硫系玻璃。利用X射线衍射、差示扫描量热分析、分光光度计、红外光谱仪等设备研究了玻璃的性能。这些玻璃具有良好的热稳定性和红外透过性能。组分为Ge23Te65Se12,Ge24Te65Se11的玻璃的差示扫描量热曲线中没有出现析晶峰,表明玻璃具有良好的抗析晶性能。组分为Ge24Te65Se11的玻璃的转变温度Tg最高,达到了188℃。这些玻璃样品的红外透过范围都很宽,从近红外的1.8μm到远红外的18μm。通过在玻璃的制备工艺中引入蒸馏提纯工艺可以有效减弱杂质吸收峰对玻璃红外透过性能的影响。最后,选用Ge23Te65Se12玻璃作为包层,Ge24Te65Se11玻璃作为纤芯,采用棒管法完成了具有纤芯包层结构的Ge-Te-Se红外光纤的拉制。     

Recent Advances in Light Scattering Calculations for Nonspherical Particles

Methods for calculating the light scattering properties of nonspherical particles are reviewed, and applications to particle characterization are considered. Angular scattering results are given for particles in fixed and random orientations. These include the Mueller matrix representation and quasi-three-dimensional computer generated plots. Spectral (wavelength-dependent) scattering results are shown for spheres, a spheroid, and a glass fiber. Applications of spectral scattering to characterizing polydisperse suspensions are discussed.     

Structure-Property Relations in Barium Borate Glasses from Raman Scattering Data

Glasses in the xBaO-(100 ? x)B₂O₃ system (x = 16–50 mol %) are investigated by Raman spectroscopy. The spectral forms of stoichiometric groupings are separated from the experimental Raman spectra. The diagram of the content of these groupings in glasses is constructed. The diagram obtained makes it possible to calculate the densities, refractive indices, temperature coefficients of linear expansion, and fractions of four-fold-coordinated boron atoms with the use of the experimentally determined partial properties of the groupings. It is revealed that the dependences of the boson peak intensity, the boson peak frequency, and the glass transition temperature on the composition of glasses in the barium borate system correlate with each other.     

Scattering and Absorption by Elongated Aerosol Particles

Recently we developed a new technique, the iterative extended boundary condition method, which is suitable for calculating the scattering and absorption by elongated particles in a broad frequency range, including at resonance. This paper briefly describes this technique, illustrates its capabilities, and presents the results of its most recent extensions. This includes the implementation of a sectioning procedure and the use of a new segmentation method for calculating scattering by very long oriented chains of aerosols. Results of absorption cross sections in two different frequency ranges, visible and infrared, and for two different polarizations, parallel and end-fire polarizations, will be presented. The range of validity of some reported relationships between scattering from a single particle and from coagulated particles are discussed. It is shown that in the end-fire polarization case the sum of the absorption by separate n particles (P _sum) is more than the absorption by a chain of n coagulated particles (P _end-fire), while in the parallel polarization case, the ratio between P _parallel/P _end-fire may be as high as a factor of 4. This observation emphasizes the importance of taking the polarization into account in calculating light scattering by elongated chains of aerosols.     

Gamma-Induced Absorption and Structural Studies of Arsenic Borate Glasses

Gamma-induced coloration in borate glasses containing arsenic was studied to secure information on: ( a ) the effect of addition of As₂O₃ on the induced coloration of the alkali borate base glass, and ( b ) the possibility of using radiation-induced coloration in studying structural changes. At concentrations of less than 10 mole % As₂O₃, arsenic takes network-modifying positions and at concentrations greater than 10.0 mole % As₂O₃, it takes network-forming positions. Between 15.0 and 25.0 mole % As₂O₃, an additional change in the structure was detected. This change may be confined to the mode of arrangement of the structural units associated with the formation of groups or compounds. Additional studies based on infrared absorption, ultraviolet absorption edge, and density measurements, as well as the chemical analysis of the glasses, confirmed the structural changes suggested from irradiation studies.     

Water Absorption and Mechanical Properties of Silica Porous Glasses

We have estimated the mechanical properties of silica porous glasses (SPG) using special two-layered structures consisting of a SPG layer on a solid glass substrate. These structures turned curved after keeping them in moist atmosphere. The linear dimensions of dry free-standing SPG wafers with the same pore size distribution increased significantly (up to 1.5%) after water vapour soaking. Bending angles of two-layered structures and the values of linear expansions were used to estimate SPG elastic constants and the mechanical stresses arising in porous glasses as the result of water absorption.