Liudmila D. Iskhakova

Coprecipitation of barium-bismuth fluorides from aqueous solutions: Nanochemical effects

The BaF2-BiF3 system was studied by the method of coprecipitation from aqueous solutions. The region of precipitation of single-phase nonoxygen powders was revealed (the atomic fraction of Bi in the initial solution was 0.35–0.43). The composition of the cubic fluorite-type phase is BaBiF5 according to an energy-dispersive X-ray spectroscopy analysis. Samples prepared from solutions with high Bi concentrations contain oxygen. This indicates that the hydrolysis temperature of BiF3 decreases when compared with that of the bulk samples and that this process takes place at room temperature. The coherent intergrowth of nanoparticles with the formation of single crystals with nonfaceted complex forms was shown by scanning electron microscopy and transmission electron microscopy.

Identification of Nanocrystalline Inclusions in Bismuth-Doped Silica Fibers and Preforms

The nature of nanocrystalline inclusions and dopant distribution in bismuth-doped silicate fibers and preforms are studied by scanning and transmission electron microscopy, and energy and wavelength-dispersive X-ray microanalysis. The core compositions are Bi:SiO2, Bi:Al2O3-SiO2, Bi:GeO2-SiO2, Bi:Al2O3-GeO2-SiO2, and Bi:P2O5-Al2O3-GeO2-SiO2. Nanocrystals of metallic Bi, Bi2O3, SiO2, GeO2, and Bi4(GeO4)3 are observed in these glasses. These inclusions can be the reason for the background optical loss in bismuth-doped optical fibers. The bismuth concentration of 0.0048±0.0006 at% is directly measured in aluminosilicate optical fibers with effective laser generation (slope efficiency of 27% at room temperature).

Peculiarities of Er3+ photoluminescence in halogen-doped amorphous silica

The spectra and photoluminescence kinetics of Er3+ ions embedded in amorphous fluorine- and chlorine-doped silica matrices synthesized by surface-plasma chemical vapor deposition were investigated at 27–300 K. Luminescence was excited with an Ar+ laser at a wavelength of 514.5 nm and with a diode laser at a wavelength of 975 nm. Narrow and well-expressed components of Stark sublevels with a small contribution of inhomogeneous broadening intrinsic to Er3+ ions in crystalline rather than amorphous matrices were revealed and identified in photoluminescence spectra. The structure of Stark sublevels was well-resolved at low temperatures. The presence of the well-resolved Stark structure in spectra was indicative of stable anion complex formation in Er3+ environment presumably associated with halogen incorporation. This environment was formed at a stage of the low-temperature plasma-chemical synthesis and was destroyed at glass fusion.

Femtosecond lasers based on dispersion compensation with hybrid fiber

The key point in fabrication of all-fiber ultra-fast lasers operating near 1 μm is utilization of fibers with anomalous dispersion. A number of works were devoted to design of specialty fibers for this aim (Photonic Crystal fibers, Photonic Bandgap fibers, hollow core fibers, high order mode fiber and etc). However none of these fiber types have found wide commercial use due to its inherent disadvantages (high nonlinearity, high loss, few-modes operation regime and etc). Recently we have developed a novel promising fiber design, so called hybrid fiber [1]. Operating hybrid mode has anomalous dispersion of 10–100 ps/(nm-km), and could be excited by simple splicing with a standard step-index fiber. Asymptotically singlemode operation regime of hybrid fiber can be obtained by introduction in the structure of absorbing layer that suppresses all unwanted modes [2].