A. A. Zhilin

Glass doped with PbS quantum dots as a saturable absorber for 1-mu m neodymium lasers

Saturable-absorber mode locking and Q switching of neodymium-doped lasers at 1.06 µm with a PbS-doped glass were demonstrated. Q-switched pulses of 0.3 µJ in energy and 15 ns in duration from a cw diode-pumped Nd3+:KGd(WO4)2 laser and ultrashort pulses of 18 µJ in energy and 70 ps in duration from a Nd3+:Y3Al5O12 laser were obtained. The saturation intensity of the PbS-doped glass (with an average semiconductor crystallite radius of 1.7 nm) was estimated to be 2.3 MW/cm2 at 1.06 µm. The bleaching relaxation time was measured to be 23 ps.

Radiative properties of Nd-doped transparent glass-ceramics in the lithium aluminosilicate system

Abstract We have studied the optical (absorption, luminescence) properties of Nd3+-doped transparent glass-ceramics obtained in the lithium aluminosilicate system. Phase composition of the glass-ceramics has been determined to affect their luminescent characteristics. We have found out that concentration quenching of neodymium fluorescence decreases upon recrystallization of β-eucryptite solid solutions (SS) into β-spodumene ones. The effect is due to partitioning of the rare-earth ions into the crystalline phase. For glass-ceramics nucleated with titania we have shown using the Judd–Ofelt theory that introduction of P2O5 in the glass-ceramic composition has a favorable effect on radiative parameters increasing noticeably the stimulated emission cross-section for the transition 4 F 3/2 → 4 I 11/2 . The influence of crystalline phase value fraction on quantum efficiency estimated from fluorescence decay measurements has been elucidated as well. It has been shown that reasonable values of the fluorescence quantum yield can be obtained provided that thermal shock resistance of materials remains sufficiently high. We have also carried out laser operation testing in a setup with flash lamp pumping. The observed spread in values of lasing characteristics can be attributed to insufficient optical quality of materials due to phase separation effects.

Linear and nonlinear optical properties of cobalt-doped zinc aluminum glass ceramics

Optical properties of cobalt-doped zinc aluminosilicate transparent glass ceramics in the visible – near-infrared (IR) spectral range have been studied. It was shown that the absorption and luminescence properties of these glass ceramics are defined mainly by tetrahedrally coordinated Co2+ ions located in ZnAl2O4 gahnite nanocrystals formed in the glass ceramic matrix. The luminescence in the visible and near IR was assigned to the transitions from the 4T1(4P) to the 4A2 and 4T2 energy levels of tetrahedrally coordinated Co2+ ion. Absorption saturation and bleaching relaxation under excitation of the 4A2→4T1(4F) transition were studied. Luminescence decay and bleaching relaxation times lie in the ranges 25–200 and 500–800 ns, respectively, depending on the Co concentration. The value of the ground-state absorption cross section of tetrahedrally coordinated Co2+ ions in zinc aluminosilicate transparent glass ceramics was estimated to be 2.0×10−19 cm2 at the wavelength of 1.54 μm.

Structural states of Ni(II) in glasses and glass-ceramic materials of the lithium-aluminium-silicate system

Abstract Optical absorption spectra of Ni(II) have been investigated in glass-ceramic materials of the lithium-aluminium-silicate system at various phase transition stages. Four types of absorption spectra have been revealed. The Ni(II) absorption bands have been attributed based on the calculation of the energy level diagram. It has been shown that in the case of heat treatment at the initial stage of phase decomposition, there arise aluminium titanium nickel regions that decompose in subsequent heating into titanium phases and aluminium-nickel spinel microcrystals. In crystallizing the main phase, i.e. solid solutions of β-eucryptite, Ni(II) is built into the structure of this phase replacing lithium isomorphously.

On the phase separation and crystallization of glasses in the MgO-Al2O3-SiO2-TiO2 system

The changes in the structure and phase composition of glasses in the MgO–Al2O3–SiO2–TiO2 system (at different TiO2 contents and ratios MgO : Al2O3) upon their heat treatment in the temperature range 700–960°C are investigated by small-angle X-ray scattering (SAXS) technique and X-ray powder diffraction analysis. The influence of gallium oxide additives on the phase separation and crystallization is analyzed. It is demonstrated that the heat treatment results in the phase separation, which occurs through the spinodal decomposition mechanism. A regular structure formed upon phase separation is retained after the completion of crystallization in inhomogeneity regions. The interference effects due to the regularity in the distribution of nanocrystals in the vitreous matrix bring about a decrease in the light scattering intensity and provide transparency of glass-ceramic materials.

Nanosized glass-ceramics doped with transition metal ions: nonlinear spectroscopy and possible laser applications

Absorption, luminescence and saturation of absorption for cobalt-doped glass-ceramics were studied. Characteristic times of 44 4 21 luminescence decay of T ( P)→ A transition for tetrahedrally coordinated Co ions in lithium-, zinc-, magnesium- and magnesium- 12 44 4 gallium-aluminosilicate glass-ceramics were evaluated to be in tens of ns time scale. Kinetics of bleaching relaxation of A → T(F ) 21 21 transition for tetrahedrally coordinated Co ions in magnesium-aluminosilicate glass-ceramics was found to be 4506150 and 120640 21 ns for 0.1 and 0.3 wt% cobalt concentration, respectively. Ground-state absorption cross-section for Co ions at 1.54 mm was estimated 219 2 to be |3310 cm . Passively Q-switched pulses from Er:glass laser of 6 mJ in energy and 80 ns in duration using the Co-doped magnesium-aluminosilicate glass-ceramics sample as saturable absorber were demonstrated.  2002 Elsevier Science B.V. All rights reserved.

A Raman Spectroscopic Study of Phase Transformations in Titanium-Containing Magnesium Aluminosilicate Glasses

The evolution of the Raman spectra of the 20MgO · 20Al2O3 · 60SiO2 glass with 10 mol % TiO2 and glasses doped with 0.5 wt % NiO or 2.5 and 5.0 mol % Ga2O3 is investigated in the course of heat treatment resulting in phase separation and crystallization. The composition and structure of the amorphous and crystalline phases (precipitating in the course of phase separation) and the residual glass are analyzed on the basis of Raman scattering, small-angle X-ray scattering (SAXS), and X-ray powder diffraction data. The size of nanoparticles of the precipitated phases is determined by low-frequency Raman spectroscopy, and the results obtained are compared with the nanoparticle size derived from the SAXS data.

Low-frequency Raman scattering of magnesium aluminosilicate glasses and glass-ceramics

Abstract The evolution of low-frequency ( −1 ) Raman scattering of titania-containing magnesium aluminosilicate (20MgO:20Al 2 O 3 :60SiO 2 with 10 mol% TiO 2 ) glasses with heat-treatment has been studied. It was found that in spectra of heat-treated glasses the intensity of the boson peak is rapidly diminished. Under certain conditions of heat-treatment schedules the boson peak disappears while the sample remains amorphous. It implies that sometimes the boson peak is missing from spectra of amorphous materials. In Raman spectra of heat-treated glasses that show the disappearance of the boson peak a new narrow highly polarized low-frequency band appears and increases in intensity. This band has been associated with a spheroidal mode of elastic vibrations in nanometer sized particles of aluminomagnesium phase formed upon phase decomposition of the glass. Its frequency changes with heat-treatment in the temperature range 750–950°C, from 50 to 17 cm −1 reflecting an increase in the sizes of corresponding nanometer particles. The composition and structure of amorphous and crystalline phases formed upon heat-treatment and also of residual glass as well were analyzed using the Raman scattering data, small angle X-ray scattering (SAXS) and X-ray diffraction (XRD) analysis.

Structural transformations of nanometer sized crystals in CoO-doped β-eucryptite-based glass-ceramics

Abstract Structural transformations of nanometer sized crystals in CoO-doped β-eucryptite-based glass-ceramics were studied by optical spectra and X-ray diffraction analysis. Four types of Co(II) absorption spectra were revealed. In the course of amorphous phase separation Co(II) ions enter into the aluminotitanate amorphous phase. Nanometer sized crystals of CoAl 2 O 4 , TiO 2 and CoTiO 3 precipitate at elevated temperature. The temperature reversible order–disorder phenomenon was revealed in spinel crystals. Nanometer sized disordered crystals of β-eucryptite solid solution precipitate after heat treatment at 720°C. At a crystallization temperature higher than 900°C, an ordering of these crystals takes place which is confirmed by the absorption spectra and the temperature dependence of lattice parameters of the unit cell.

The structure of luminescence centers of neodymium in glasses and transparent glass-ceramics of the Li2O-Al2O3-SiO2 system

Abstract The structure of luminescence centers of Nd3+ in lithium aluminosilicate glasses and glass-ceramics has been studied. A correlation was obtained between spectroscopic parameters, the character of phase transformations in the course of conversion to glass-ceramics and the precipitated phases. In crystallization of β-eucryptite solid solutions, the greater part of Nd3+ ions remains in a residual glassy phase. Under re-crystallization of these solid solutions into β-spodumene solid solutions, Nd3+ ions enter the β-spodumene structure. The conclusion was drawn regarding the chemical properties of the second coordination sphere of the Nd3+ ions.