L. V. Maksimov

Physical consequences of inhomogeneous glass structure from scattered light spectroscopy data

Abstract Micro-inhomogeneous glass structure is investigated on the basis of scattered light spectroscopy including both Rayleigh and Mandelshtam-Brillouin scattering spectroscopies (RMBS) and Raman scattering spectroscopy (RS). The Na2OB2O3, Na2OSiO2, R2OGeO2, RFGeO2 (R = Na, K) glass systems are examined. RMBS spectra include the Rayleigh scattering component at the incident light frequency, ν, the intensity of which is determined with the “frozen-in” density and concentration fluctuations and Mandelshtam-Brillouin scattering components shifted by ± Δν the intensities of which are determined by “non-frozen” density fluctuations. Glass composition relationships of spectral intensity components (Landau-Placzek ratio), RL−P = IRayl./2IM−B, characterizing changes in micro-inhomogeneous structure with composition are calculated. Glass composition areas with maximum and minimum homogeneity are defined and their connection with miscibility gaps is established. Introduction of doped ions into the glasses is shown to lead to their selective entrance into fluctuation matrix micro-inhomogeneities enriched with alkali ions (segregation of doped ions) that causes an increase of Rayleigh scattering in doped glasses. In the spectral region of 50–1500 cm−1 the measured RS spectra are related to identified fragments on the basis of which decomposition into components belonging to fixed stoichiometry groups (constant composition groups ≡ CCG) is made. Concentrations and partial properties of CCG are determined. CCG are regarded as true glass components. RMBS spectroscopy data are compared with RS spectral data. A correlation is established between glass composition relationships of RL−P and CCG concentrations: glasses with minimum Rayleigh scattering intensity have single-type CCG. “Frozen-in” concentration fluctuations defining Rayleigh scattering are attributed to CCG concentration fluctuations.

Medium-range order and physicochemical properties of (100 − x)(0.5PbO · 0.5P2O5) · xTeO2 glasses in terms of the constant stoichiometry grouping concept

Glasses in the (100 − x)(0.5PbO · 0.5P2O5) · xTeO2 section of the PbO-P2O5-TeO2 system have been synthesized over the entire composition range for the first time and their properties (Raman spectra, refractive index n, density d, glass transition temperature Tg, and light scattering losses) have been investigated. It has been demonstrated that the Raman spectra can be represented as a superposition of constant spectral forms corresponding to constant stoichiometry groupings PbO · P2O5, TeO2 · 2PbO · 2P2O5, TeO2 · PbO · P2O5, 2TeO2 · PbO · P2O5, and TeO2. The existence of crystals of the corresponding stoichiometry has been predicted using the constant stoichiometry grouping concept. The diagram of the constant stoichiometry grouping contents (determined from the Raman spectra) in glasses of the system under investigation has made it possible to determine the partial properties of constant stoichiometry groupings, to calculate the dependences of the refractive index and density on the composition, and to refine the values of n and d for vitreous tellurium dioxide and lead metaphosphate. The practical importance of glasses in the system under consideration for the use in photonic devices has been discussed.

Medium-range order of radiation modified silica glasses studied by spectroscopic and optical methods

Abstract Neutron irradiated silica glasses were studied. The increase of density and refractive index with the fluence value were found and Rayleigh and Mandelshtam-Brillouin scattering, low-frequency Raman scattering and Raman scattering spectra were measured. It was concluded that neutron irradiation of silica glasses led to an alteration of a microinhomogeneous glass structure including correlation regions and ‘frozen’ density fluctuations.

Vitreous Materials for Electrooptics

A complex approach to the development of electrooptic glasses is proposed. The approach is based on the use of the traditional methods of structural-physical investigations in combination with the Rayleigh and Mandelstam-Brillouin scattering spectroscopic techniques. The structural features of niobate glasses and their properties are considered. It is shown that niobium selectively enters into the fluctuation microinhomogeneities in the alkali borosilicate vitreous matrix. The conditions for the precipitation of sodium niobate microcrystals are determined, and their influence on the increase in the Kerr constant for glass-ceramic materials is analyzed.

Spectroscopic properties of highly concentrated Nd3-doped antimony-phosphate glass for microchip lasers

The alkaline antimony-phosphate glass doped with Nd3+ was synthesized under different conditions with the controlled content of OH groups. The Nd2O3 concentration varied in the range of 0.2–2.0 mol %; the Sb2O5 concentration was 20 mol %. The absorption and Nd3+ ion luminescence spectra and the absorption spectra of OH groups were obtained. Quenching of the Nd3+ ion luminescence depending on the Nd2O3 and OH group concentrations was studied. It was found that the optimized spectroscopic and kinetic parameters of glass (emission cross section, emission width, radiative lifetime) are close to the parameters of the SCHOTT GLAS industrial laser glass. It was shown that the immediate environment of Nd3+ ions is formed by phosphate polyhedra.

Spatial Distribution of Heavy Metal Ions in Glass Forming Melts: Spectroscopic and Physical-Chemical Study

Spatial distribution of heavy metal ions (HMI) in inorganic glass forming melts was studied by measuring HMI distribution coefficient between two unmixable melts: sodium-borate glass forming melt and non-glass forming molten sodium sulfate. Combining the data on glass host composition dependence of HMI distribution coefficient with the data of Rayleigh and Mandel’shtam-Brillouin scattering (RMBS) spectroscopy of glasses doped with HMI and undoped ones made it possible to evidence the segregation of HMI into alkali-enriched inhomogeneities of glass hosts and offer the approach to choosing compositions of glass host in which HMI segregation will be minimized.

Radiation of novel type emitted by microchip laser

Novel highly concentrated Yb/Er and Nd phosphate glasses were elaborated and microchip lasers were produced. Lasing parameters of Yb/Er and Nd phosphate glasses were studied. Novel type of radiation excited by pumping power sufficiently high for amplification of radiation but lower than lasing threshold was observed. It was found that indicatrix and spectrum (comb spectrum) of this radiation differed from the parameters of both luminescence and lasing radiation. It was found that the modulated radiation emitted by the micro-chip lasers was super luminescence. Spectral separation between adjacent lines of comb spectrum varies with radiation wavelength, length of Fabry-Perot resonator and refractive index of amplifying medium. The phenomenon of super luminescence modulation in Fabry-Perot micro resonator can be used for designing the simplest comb spectral channels generators for DWDM working in 0.9-1.6 &mgr;m spectral range. 200 and 250 spectral channels were realized for Yb/Er and Nd microchip lasers, correspondingly.

Structural peculiarities of phosphate glasses for fiber optic applications

Alkali phosphate, phosphate-silicate, and phosphate-germanate glasses were studied by means of high-temperature acoustics and Rayleigh-Mandelstam-Brillouin (RMBS) and Raman scattering (RS) spectroscopies. Temperature-temporal dependences of the ultrasound velocity in the glass melts were measured at temperatures up to 1550°C. From the RMBS spectra the Landau-Placzek ratio and frequency shifts were found. A theory of the fluctuations fieezing at the cooling of the glass melt was applied to separate the contributions of the frozen-in density and concentration fluctuations to the Rayleigh scattering losses. A comparison was drawn with the losses in silica glass. The RS spectra allowed the identification of the constant-stoichiometry groups. The feasibility of the system xNa2O-(40 - x)K20-30Al203-30P205 for the fabrication of low-scattering glasses was ascertained.

Nanostructure of glasses: experimental evidence

Inorganic glass is material having nanoscaled physical and chemical inhomogeneities ad initio because glass inherits thermodynamic fluctuations of concentration, density and anisotropy of a glass forming melt. Combining light scattering and high temperature acoustics data allows to use the effect of internal immersion for designing multicomponent glasses with Rayleigh scattering losses lower than those of the silica glass. Non-random spatial distribution of dopants including rare-earth (RE) ions in a glass host (doped ion segregation) causes excessive Rayleigh scattering losses and enhancement of RE ion-ion interaction. Therefore, it opens the way to optimize operation parameters of laser and up-converting glasses by the proper choice of glass host composition. Results of Raman scattering spectra processing and characterization of electrooptical (EO) sensitivity of niobate glasses showed the existence of groups with stoichiometry of the well-known EO crystals and crystal-like orderliness (crystal motifs) in the glasses as the necessary condition of high EO sensitivity. It was found that EO sensitivity of glasses could be essentially increased by thermal treatment.