Yu. K. Fedorov

Mechanical properties of phosphate glasses as a function of the total bonding energy per unit volume of glass

The dependences of the structural strength and the elastic modulus on the chemical composition of phosphate glasses are analyzed. The structural strength and the elastic modulus of phosphate glasses are determined for different types of both the modifier ion and the second glass-former (B2O3 or SiO2) introduced into the glass. The total bonding energy per unit volume of the glass is calculated from the data on the dissociation energy for the oxides entering into the glass composition and the data on the atomic packing density. For four systems of phosphate glasses, it is demonstrated that the Young’s modulus depends linearly on the total bonding energy per unit volume of the glass. The dependence of the structural strength on the chemical composition exhibits a more complex behavior and is governed by other additional factors, such as the formation of new structural groups or the change in the structure of the anionic network of the glass.

Effect of Coloring Impurities on the Absorption in Neodymium Phosphate Laser Glass at a Lasing Wavelength

This paper reports on the results of the investigation of KGSS 0180/35 neodymium phosphate glasses produced on an industrial scale under oxidizing conditions and glasses prepared under experimental conditions in which iron and copper in small amounts rather than neodymium are introduced into the glass composition. The experimental glasses are synthesized by varying the redox conditions of melting. The oxidation states of transition metal impurities (Cu, Fe, V, Ni, Co) and the nonactive absorption coefficients of glasses at the lasing wavelength are determined. It is revealed that the main contribution to the nonactive absorption coefficient of the KGSS 0180/35 glass produced on an industrial scale is made by Cu2+ ions at a concentration higher than 0.5 ppm. At a lower copper concentrations, the total contribution of Fe2+, V4+, Ni2+, and Co2+ impurity ions to the nonactive absorption coefficient is comparable to that of Cu2+ ions. It is demonstrated that a decrease in the concentration of coloring impurities in glasses and the optimization of redox conditions of melting make it possible to prepare phosphate laser glasses with a nonactive absorption coefficient of the order of 0.001 cm−1. In terms of the nonactive absorption coefficient, these glasses are on a par with similar glasses of foreign manufacture and satisfy the requirements imposed on glasses by developers of high-power high-energy laser facilities.

Influence of the redox conditions of melting on the quantitative ratio of ions Fe2+/Fe3+ in aluminum potassium barium phosphate glass

This paper reports on the results of the investigation of the KGSS 0180 phosphate laser glasses produced under industrial conditions, in which iron is contained in the form of impurities, and the glasses prepared under laboratory conditions with iron additives and a composition similar to that of the KGSS 0180 glass matrix. The influence of the redox conditions of glass melting on the quantitative ratio of ions Fe2+/Fe3+ in the glass composition and on the contribution of Fe2+ ions to the inactive absorption coefficient at the lasing wavelength (1.053μm) is analyzed.

Properties of neodymium-doped aluminophosphate laser glasses

Neodymium-doped glass lasers for obtaining high average output require the development of high-efficiency technological compositions of laser glasses, combining superior thermomechanical qualities with good laser and optical properties. Intermediate-power lasers, with neodymium-doped glass as the active element, have limited energy capabilities because of the temperature gradient that is induced in the glass during operation and causes the active element to fracture. In order to compare the thermomechanical properties of laser glasses with different compositions we calculate the quality factor (RT*) [I] for the given active material from the formula

Influence of Boron Oxide on the Physicomechanical Properties of Glasses in the Li2O–B2O3–P2O5 System

The mechanical properties of glasses in the Li2O–B2O3–P2O5 system are investigated as a function of the boron oxide content in the range from 5 to 30 mol % at a constant lithium oxide content of 45 mol %. It is demonstrated that, as the B2O3 content increases, the density of glasses passes through a maximum at 20 mol % B2O3 and the molar volume decreases gradually. The elastic modulus and the hardness of glasses monotonically increase with an increase in the B2O3 content. An increase in the B2O3 content leads to a decrease in the structural strength (measured using the method of three-point bending of fibers) and the fracture toughness (determined by the microindentation technique). The assumption is made that the decrease in the strength characteristics is caused by the phase separation developed in the structure of lithium phosphate glass with an increase in the B2O3 content.

Glass for high-peak power high-energy generators and radiation amplifiers

The quality-related factors of neodymium- and copper-containing phosphate glass for big disc and high-aperture rod active elements of high-peak power high-energy radiation amplifiers and generators have been considered. The functionally important parameters of the mentioned glass are given.

How process factors affect the limiting characteristics of neodymium phosphate glasses for large disk- and rod-shaped active elements

This paper lists the requirements imposed by the designers of powerful high-energy lasers and radiation amplifiers on KGSS 0180 phosphate glasses with various neodymium concentrations, used to manufacture large disk- and rod-shaped active elements. The classical two-stage technology for melting them is described, and a quantitative characterization is given of the extent to which structural water and the neodymium concentration in the glasses affect the maximum achievable luminescence time and quantum yield. A description is given of why inactive absorption of radiation appears at the lasing wavelength and a method for reducing it in the resulting glasses. A method is indicated for reducing the number of inclusions of metallic platinum in the glass, which affect its radiation strength.

Gain spectra in ytterbium-erbium metaphosphate glasses for microlasers

Direct measurements of the gain/loss spectra for the principal transition of the erbium ion (1.5μm) in ytterbium-erbium phosphate glasses as a function of the concentration of ytterbium ions and the laser pump power have been carried out. The ytterbium concentration was varied from zero to the limiting value of 52.4×1020cm−3. It is shown that increasing the ytterbium concentration, beginning with NYb=20.9×1020cm−3, results in a reduction of the gain threshold. On glass with the limiting ytterbium concentration (ytterbium metaphosphate), population inversion is achieved at low pump powers of 35mW. The largest gain of 0.1cm−1 is obtained on a sample 0.5mm thick with ytterbium concentration 41.7×1020cm−3 and erbium concentration 0.29×1020cm−3 with an absorbed pump power of 210mW.

Large disc-shaped active elements made from neodymium phosphate glass elements made from neodymium phosphate glass

A technology has been developed for the production of large active elements made from KGSS 0180/35 neodymium phosphate glass (with a neodymium ion concentration of NNd53.5 x1020cm-3), iintended for powerful pulsed lasers with high output radiation energy. The neodymium glasses were melted using a two-stage or single-stage process with high-purity reagents in crucibles made from dispersion-strengthened platinum or a newly developed highstrength cristobalite refractory, which, along with other process methods, makes it possible to obtain glass that contains no metallic platinum inclusions. The main elements of the process for synthesizing neodymium glass are deep oxidation of the melt with dry oxygen in order to convert traces of platinum and iron to higher valence states and simultaneously eliminate hydroxyl group impurities, as well as the use of a nonplatinum refractory to fabricate the glassware. The resulting glasses are characterized by high optical homogeneity, high luminescence lifetime of the neodymium ( t~300 us), radiation strength to 33 J/cm2 when the exciting pulse width is 3?4 ns, and a nonactive absorption coefficient at the lasing wavelength of about 0.0015 cm-1. The required high-quality surface processing of the active elements is provided by fine annealing of the blanks and by using grinding?polishing equipment with program control.

Neodymium- and copper-bearing phosphate glasses for fabricating large rod-shaped and disk-shaped active elements of lasers and heavy-duty high-energy radiation amplifiers

This paper analyzes the requirements imposed on laser glasses intended for the fabrication of rod-shaped and large disk-shaped active elements with a large aperture for generators and heavy-duty radiation amplifiers. Quantitative data are presented concerning the maximum achievable values of the functionally important basic characteristics of domestically produced neodymium phosphate glasses and the copper-oxide-doped glasses from which absorbing shells (cladding) are fabricated that suppress superluminescence and stray lasing in disk-shaped active elements.