This paper discusses the features of objectives intended for amateur and professional astronomical observations. Type-OK4 crown glass with special dispersion behavior is used to achieve apochromatic correction in refracting objectives, since the technology for obtaining high-quality blanks made from this glass makes it possible to create apochromatic objectives with an entrance-pupil diameter of up to 304 mm. Experimental compositions of the glass have been developed that make it possible to obtain apochromatic systems composed of two lenses. (c) 2013 Optical Society of America.

The Lytkarino Optical Glass Factory produces unique optical materials, such as glass–crystalline materials with zero thermal linear-expansion coefficient, doped laser glasses, glasses with special dispersion behavior for apochromatic objectives, and glasses for operation in the visible and IR regions. High quality of the glasses produced by the factory is ensured by upgrading the technological processes of glass production and modernizing the glass melting, annealing, and equipment processing, as well as by introducing new apparatus and methods for monitoring the properties.

The easy-to-fabricate, phosphate-based laser glass LFS5 has been developed, with parameters at the level of the phosphate glasses of the leading producer Countries. A process has been adopted for producing LFS5 glass of high optical quality for large active elements in the form of rods up to 1000 mm long from a glass melt in a platinum crucible of moderate volume. (C) 2004 Optical Society of America.

The crystallization of the x K 2 O · x Nb 2 O 5 · (1 – 2 x )SiO 2 ( x = 0.167–0.250) glasses and glasses close in composition to K 2 O · Nb 2 O 5 · 4SiO 2 at the ratio K 2 O : Nb 2 O 5 ≠ 1 is investigated. In high-silica glasses, the metastable phase separation followed by the bulk multiphase crystallization are observed at temperatures close to the glass transition point T g . The nanostructured transparent glasses that exhibit the optical second harmonic generation (SHG) effect are formed at the early stages of phase separation. The surface crystallization of glasses with the precipitation of the KNbSi 2 O 7 noncentrosymmetric phase occurs at higher temperatures.

Complete set of infrared reflection and Raman scattering spectra of LaBGeO5 and Pb5Ge3O11 glasses and crystallised glasses was measured in a broad frequency and temperature range. Comparison with the spectra of crystals showed that the short range order in the glasses and in the corresponding crystals is very similar.

Crystallization behavior of potassium niobium silicate (KNS) glasses having compositions expressed by the general formula xK2O·xNb2O5·(1 ‐ 2x)SiO2, with x= 0.167, 0.182, 0.200, 0.220, and 0.250, has been studied by DTA, X‐ray diffraction, second harmonic optical generation (SHG), and electron microscopy. Bulk crystallization of potassium niobates in glasses with compositions near K2O·Nb2O5·2SiO2, as well as surface crystallization of KNbSi2O7 phase, has been established. Transparent glass‐ceramics, based on potassium niobates with remarkable SHG signal values, can be obtained from glasses with the lowest silica content, by heat treatment at temperatures just above Tg, while at higher temperatures from all of the glasses under investigation the main crystallizing phase is KNbSi2O7 ferroelectric. Applying a dc electric field, grain‐oriented crystallization is produced in KNS glasses with development of significantly anisotropic arrangements of KNbSi2O7 crystallites.

Under appropriate conditions (high temperature gradient, rapid heating and following prolonged isothermal treatment, suppression of bulk crystallization, polished glass surface, etc.) the La2O3-B2O3-XO2 (X = Si, Ge) systems glasses are crystallized in preference on the surface with formation of perfect textures based on needle-shaped stillwellite-like crystals of the LaBXO5 composition. Lanthanum borogermanate (LBG) glasses exhibit more intense texture-forming ability than lanthanum borosilicate (LBS) ones. Glass ceramic textures with a degree of grain orientation up to 0.9 in the LBG system are obtained. The pyroelectric coefficient values of the best of synthesized LBG textures are as high as 0.5–1.5 nC cm−2 K−1 in a wide temperature range. A poor crystallization ability of the LBS glasses at temperatures less than 1000°C supposed to be used in preparing both thin polar crystalline films on the glass surface for nonlinear optical applications and ferroelectric (pyroelectric) glass ceramics by the powder technology.

Ten glasses close in composition to the stoichiometry of the LaBSiO5 stillwellite-like phase are synthesized, and the specific features of glass synthesis are discussed. The glass properties (density, thermal expansion, T-g, permittivity and dielectric loss at a frequency of 1 MHz, and volume de resistance) are measured, and the crystallization of glasses is studied. The crystallization field of the LaBSiO5 stillwellite is constructed. A narrow region of compositions and heat treatment conditions are determined at which the glass-ceramic samples with ferroelectric properties can be obtained. These samples are characterized by a step change in the temperature curve of the optical second harmonic signal I-2 omega in the temperature range 120-140 degrees C. The appreciable value of dl(2 omega)(T)/dT suggests that the LaBSiO5-based glass-ceramic materials possess both ferroelectric and pyroelectric properties.

It is experimentally shown that glass-ceramic textures based on the LaBGeO5 stillwellite-like phase can be manufactured by techniques of isothermal crystallization, gradient crystallization of glass plates or small glass bars, and crystallization of glass plates under the conditions of their axial compression. The effect of the quality of glass surface and heating rate on the texture formation is studied under isothermal conditions. The dense glass-ceramic textures with degree of grain orientation up to 0.8 are obtained. Electron microscopy makes it possible to clearly observe the texture in the form of well-defined needle-shaped LaBGeO5 crystals, which grow, for the most part, normally to the glass surface. The temperature dependences of the permittivity for samples cut in parallel and perpendicular to the surface are measured. These dependences confirm the high degree of sample texturing and provide a way of revealing the ferroelectric phase transition along the polar axis at 515 degrees C, which is close to the temperature of such a transition in the LaBGeO5 single crystal. The pyroelectric coefficient for the best textures obtained is about 0.5-1.5 nC/(cm(2) K) over a wide range of temperatures. There are considerable potentials of increasing this coefficient through both the optimization of composition, glass melting, and glass-making and the texturing process.

The geometry, refractive indices and dispersion of the H4P2O7 structural unit were calculated by the MNDO CI (configurational interactions) semi-empirical molecular orbital method. The optimized geometry and calculated properties showed a good agreement with the experimentally determined data. The absorption edge was found to be 100 nm. Using Sellmeier's dispersion formula with the assumption that λ1 = 100 nm and nD = 1.503, a number of refractive i ndices of P2O5 glass and then dispersion coefficient were calculated. Abbe value, νD, proved to be 60.6, which was in a good correlation with experimental data determinated by Kordes (60.6). It was concluded that the MNDO CI approach may be employed for estimating optical properties of different oxides and materials when direct measurements are not available.

This paper presents the experimental results of an investigation of the dependence of local damage concentration in GLS6 glass on the absorption coefficient for the one-time irradiation of large volumes of glass (100 cm3) by a 40-nsec neodymium-laser pulse. An increase in concentration is observed with an increase in absorption from 0.46 to 1.0 cm-1. The nature of the microdefects that result in local laser damage of GLS6 glass by short (40-nsec) and of K8 glass by long (1-msec) pulses was investigated.