Transparent Cr2+-doped ZnS ceramics with a nominal Cr concentration ranging from 50 to 3000 ppm were fabricated by hot pressing. ZnS nanopowders with controlled Cr content were synthesized by a combustion method and treated in H2S/N-2 to remove oxide impurities. X-ray diffraction showed that both powders and ceramics were predominantly cubic ZnS with minor hexagonal ZnS; impurity phases (ZnO, Zn3O(SO4)(2)) present after combustion were eliminated. Powders consisted of similar to 100 nm primary particles, and doping had little effect on morphology. Ceramics achieved >99.5% theoretical density with similar to 0.7 mu m grain size, regardless of Cr content. Undoped ceramics exhibited mid-infrared transmission near the theoretical limit (similar to 75%); increasing Cr content reduced transmission (though still being high up to 1000 ppm) and introduced visible absorption attributed to Cr3+ in a ZnCr2S4 spinel phase. Optical spectra revealed broad Cr2+(T-d) related absorption (1.3-2.1 mu m, peaking at similar to 1.7 mu m) and broad luminescence (1.6-3.0 mu m, peaking at similar to 1.91 mu m). A luminescence lifetime of similar to 6 mu s was measured for all samples indicating that quenching effects are limited in the investigated range. These results demonstrate that Cr2+:ZnS ceramics have promising mid-IR emission properties suitable for 2-3 mu m solid-state lasers.

This work investigates Tm3+-doped sesquioxide ceramics based on gadolinia and its binary and ternary solid solutions with yttria and lutetia as promising gain media for similar to 2 & micro;m lasers. Transparent ceramics containing 3 at.% Tm3+ were fabricated by hot pressing of solid-solution nanopowders. Their thermal conductivity systematically decreases with increasing compositional complexity, consistent with enhanced phonon scattering in multicomponent lattices. At 298 K, the thermal conductivity ranges from 8.6 W & centerdot;m(-1)& centerdot;K-1 for Tm:Gd2O3 to 3.8 W & centerdot;m(-1)& centerdot;K-1 for the ternary (Tm0.03Gd0.323Y0.323Lu0.323)(2)O-3 composition, while the linear thermal expansion coefficients lie between 4.7 and 6.6 ppm & centerdot;K-1. The addition of lutetia effectively suppresses grain growth: (Tm0.03Gd0.485Lu0.485)(2)O-3 and (Tm0.03Gd0.323Y0.323Lu0.323)(2)O-3 ceramics exhibit submicron average grain sizes, whereas the binary solid solution (Tm0.03Gd0.485Y0.485)(2)O-3 shows coarser grains of about 7 & micro;m in size. Spectroscopic studies reveal that the incorporation of smaller Gd3+ cations weakens the crystal field around Tm3+ ions, enabling controlled blue shifts of the emission peak down to 2050 nm compared with Sc2O3-, Y2O3-, and Lu2O3-based matrices. Compositional disorder in mixed-cation lattices induces strong inhomogeneous broadening, yielding smooth and wide emission bands favorable for broadly tunable operation of similar to 2 & micro;m lasers.

The magneto-optical and thermo-optical characteristics of high-purity germanium crystals of different isotopic compositions were studied to assess the applicability of this material as a magnetoactive medium for Faraday isolators for high-power radiation in the mid-IR range. An increase in the Verdet constant with increasing atomic mass of the isotope was observed in experiments. The physical mechanisms arising from the quantum theory of the Faraday effect associated with interband transitions, which can explain this dependence, are discussed. No isotopic variations in the thermo-optical characteristics that determine the maximum operating power of Faraday isolators of conventional design were observed. The results of measurements at a wavelength of 1940 nm demonstrated the possibility of constructing a Faraday isolator with one magneto-optical element at an operating power over 100 W and an isolator with compensation of thermally induced depolarization using a reciprocal rotator at an operating power surpassing 200 W. The prospects of using Ge crystals for developing Faraday isolators for longer wavelength radiation were discussed. The use of radiation with wavelengths greater than or similar to 2 mu m opens up broad opportunities for increasing the operating power of isolators based on various schemes and for creating broadband isolators.

Alumina - 7.5 wt% yttria-stabilized zirconia (YSZ) ceramic composites were sintered using 24 GHz microwave heating at rates of 10 - 200 degrees C/min with zero isothermal hold. The starting powders were nanophase i-Al2O3 and YSZ prepared by a laser evaporation method. The final densities of the sintered samples were up to 97.5 % of the theoretical value. The samples exhibited rapid densification until transformation to the alpha-Al2O3 phase. The temperature of the densification rate peak (and hence of the phase transformation) decreased consistently with increasing microwave electromagnetic field intensity (varied by using different susceptor materials). The densification peak temperature difference between microwave and conventional sintering experiments exceeded 200 degrees C.

We report on the fabrication and optical properties of erbium-doped Y2O3-MgO and Gd2O3-MgO nanocomposite ceramics, with a particular focus on their mid-infrared emission. The ceramics were fabricated by a self-propagating high-temperature synthesis followed by hot pressing. The transmittance of 1.7 mm-thick 5 at.% Er:Y2O3-MgO and 7 at.% Er:Gd2O3-MgO ceramics at 3 mu m amounted to 79.4% and 21.5%, respectively. This difference in transmission, as revealed by microstructural analysis, is due to variation in the distribution of residual pore sizes, while the average grain size is almost the same for both ceramics, being similar to 200 nm. The composites exhibited luminescence in the visible, near-infrared, and mid-infrared spectral ranges attributed to electronic transitions of Er3+ ions in the cubic sesquioxide phase. Peculiarities in the Raman and luminescence spectra were identified in comparison to single-phase Er:Y2O3 and Er:Gd2O3 ceramics, which may indicate certain solubility of MgO in the sesquioxide phase of the composites.

Pulsed waveguide lasers emitting around 3 $\mu \mathrm{m}$ are envisioned as seed sources for amplification and frequency down-conversion towards mid-infrared. The waveguide architecture benefit from suppressing the parasitic water vapor absorption in the air, intrinsically good mode matching, low thresholds, and compatibility with the fiber technology. We report on a $3-\mu \mathrm{m}$ waveguide laser passively Q-switched by $\text{Fe}^{2+}$ -doped ZnSe. The latter material is known for its ultrabroadband nonlinear absorption in the mid-infrared [1].

Extending the transparency range of MgO-Y2O3 composite ceramic to wavelength less than 3 μm is highly desirable, as it broadens their potential applications in infrared (IR) optics. This study illustrates the effectiveness of deagglomerating a mixture of magnesium oxide and yttrium sesquioxide powders, derived from self-propagating high-temperature synthesis (SHS), in achieving this goal. The impact of powder deagglomeration on the microstructure and porosity defects of hot-pressed MgO-Y2O3 ceramic was analyzed using electron and IR microscopy. The results showed that the deagglomeration enhanced the homogeneity of the composite grain mixture, slowed down the grain growth, suppressed the formation of large grains, and significantly reduced the number of porosity microdefects in the material. The optical transmittance increased from 42% to 77% at a wavelength of 2 μm (for samples with a thickness of 1.2 mm) when deagglomerated powders were used, compared to non-deagglomerated ones.

The luminescence kinetics of $\mathbf{A l}_{2} \mathrm{O}_{3}-\mathrm{Ce}: Y A G$ composite ceramics with $0.05-0.3 \mathrm{at} \% \mathrm{Ce}^{3+}$ doping has been investigated in this paper. Using synchrotron radiation with an initial pulse duration of 1 ns and a fitting model in the form of temporal convolution of the initial pulse with the decay exponent allowed us to identify two modes in the decay process. For the fast mode a time constant is growing from $\sim 1-1.5$ up to $\sim 3 \mathrm{~ns}$ and its fraction is decreasing from $\sim 20-40 \%$ down to $\sim 13-14 \%$ while Ce concentration is increasing from 0.05 up to $0.3 \mathrm{at} \%$. Among the literature data, one can find both contradictory to the results obtained and supporting them. Comparison with studies of thermal quenching in $\mathrm{Ce}^{3+}$-doped phosphors suggests an effective equivalence between the effects of SR and elevated temperatures on luminescence kinetics. Confirmation of the hypothesis requires additional studies on the effect of dose load from SR on the parameters of luminescence kinetics.

An IR-transparent magneto-optical Dy2O3-MgO compositeceramics was fabricated by vacuum hot pressing of glycine-nitrate self-propagating high-temperature synthesized nanopowders. Composites significantly outperform dysprosium sesquioxide ceramics in terms of thermal conductivity and mechanical properties.The HV1 microhardness of the Dy2O3-MgO composite is 9.9 GPa and the fracture toughnessKIC, calculated by the Palmquist method, is 1.7 MPa m1/2. The thermal conductivity of the composite was measured in the range of 50-300 K and is 10.6 W/(m K) at room temperature. The transmittance of 1.5 mm thick Dy2O3-MgO sample is about 70 % in the wavelength range -2.1-2.2 mu m and more than 80 % in the range -3.6-6.5 mu m, which is close to the theoretical value for dysprosium sesquioxide.The value of Verdet constant of Dy2O3-MgO composite ceramics is 7.0 +/- 0.3 rad/(T center dot m)at 1940 nm.

Strontium fluorarsenate Sr5(AsO4)3F optical ceramics were fabricated for the first time by vacuum hot pressing of chemically precipitated powders. The properties of these ceramics were compared with those of the well-known strontium fluorophosphate Sr5(PO4)3F. According to BET, X-ray diffraction, and scanning electron microscopy, Sr5(AsO4)3F and Sr5(PO4)3F powders have an isomorphic single-phase structure and similar particle sizes of about 100–200 nm. The transmittances of 1.5 mm thick samples are as high as 89.5% and 85.8% in the mid-IR for Sr5(AsO4)3F and Sr5(PO4)3F, respectively. The Sr5(AsO4)3F ceramics have a wider mid-IR transmission range (up to 5.8 μm) than the Sr5(PO4)3F ceramics (up to 4.5 μm).

We present a detailed spectroscopic study of Tm3+ ions in stoichiometric and "mixed" (solid-solution) cubic (C-type, sp. gr. Ia (3) over bar) sesquioxides R2O3 (RY, Lu, Sc or their mixture), with the goal of developing broadband-emitting gain media for ultrafast lasers at similar to 2 mu m. Evidence of a linear variation (increase) of the crystal-field strength when decreasing the ionic radius of the host-forming cation R3+ in the isostructrural R2O3 series is presented. The crystal-field splitting of Tm3+ multiplets is determined for C-2 sites and justified using a barycenter plot, and the first evidence of C-3i Tm3+ species is presented. A remarkable inhomogeneous spectral broadening for compositionally "mixed" sesquioxides (in particular with Sc3+) with respect to the parent compounds is revealed at low temperatures. It is proven that binary and ternary "mixed" R2O3 compounds form substitutional solid-solutions with a mixing of the host-forming cations at the atomic level. The stimulated-emission and gain cross-sections for the F-3(4) -> H-3(6) Tm3+ transition are determined. Guidelines for material engineering of Tm3+-doped gain media for mode-locked 2-mu m lasers are also provided.

Samples of alumina - 3 % yttria-stabilized zirconia (YSZ) composites were sintered in rapid processing regimes using 24 GHz microwave heating at rates of up to 200 degrees C/min and zero hold time. The final relative density was 96-99 % for the samples containing 1.5 and 7.5 wt % YSZ and 98-99 % for the samples containing 13 wt % YSZ. The microwave sintering kinetics were compared for the processes carried out by direct and susceptor-assisted microwave heating. Under direct microwave heating, the effect of an intense microwave electromagnetic field with an estimated absorbed power density of up to 130 W/cm(3) resulted in a shift of the shrinkage curves by about 100( degrees )C towards lower temperatures compared to the case of susceptor-assisted heating. The grain size of the samples sintered by direct microwave heating decreased with an increasing heating rate. The mechanical properties were slightly higher for the materials sintered under susceptor-assisted microwave heating. The samples containing 13 wt % YSZ exhibited a microhardness of about 20 GPa and a fracture toughness of about 7 MPa m (1/2) .

The influence of mechanical grinding conditions of high-purity chemical vapor deposition (CVD) zinc selenide (ZnSe) powders on their particle size distribution, their sintering process, and the transparency of optical ceramics has been studied. Powders with an optimal granulometric composition have been obtained, having an average particle size of 0.3 μm with a maximum of not more than 1 μm. These parameters have been achieved by grinding the powders in a planetary ball mill for 20 h at a grinding jar rotation speed of 150 rpm. ZnSe optical ceramics have been fabricated by a combination of hot pressing and subsequent hot isostatic pressing of CVD powders. The maximum transmission for 2 mm thick samples has been 69

α-Si3N4-based powder composites containing 3 wt

High-average-power narrow-linewidth tunable solid-state lasers in the wavelength region between 2 and 3 μm are attractive light sources for many applications. This paper reports a narrow-linewidth widely tunable laser system based on the polycrystalline Cr2+:ZnSe elements pumped by repetitively pulsed 2.1 µm Ho3+:YAG laser operating at a pulse rate of tens of kilohertz. An advanced procedure of ZnSe element doping and surface improvement was applied to increase the laser-induced damage threshold, which resulted in an increase in the output power of the Cr2+:ZnSe laser system. The high-average-power laser system comprised double master oscillators and power amplifiers: Ho3+:YAG and Cr2+:ZnSe laser oscillators, and Ho3+:YAG and Cr2+:ZnSe power amplifiers. The output wavelength was widely tuned within 2.3–2.7 µm by means of an acousto-optical tunable filter inside a Cr2+:ZnSe master oscillator cavity. The narrow-linewidth operation at the pulse repetition rate of 20–40 kHz in a high-quality beam with an average output power of up to 9.7 W was demonstrated.

A high-efficiency widely-tunable laser system based on homemade polycrystalline Cr 2+ :ZnSe pumped by repetitively-pulsed Ho 3+ :YAG lasers was created. The system consisted of a narrow-line tunable Cr 2+ :ZnSe master oscillator and power amplifier with a variable pulse repetition rate between 10 and 40 kHz. The electronic wavelength tuning at 2.3-2.5 μm was provided by an intracavity acousto-optic filter. The average power and pulse-train energy of the high-quality laser beam at 2420 nm were 8–9 W and 80 mJ, respectively. These values were achieved in a pulse burst with a repetition rate of 10–2000 Hz. The laser system was designed for the purpose of environmental monitoring within the transparency window of the Earth's atmosphere.

Ho:R 2 O 3 (R = Y, Lu, Sc) transparent sesquioxide ceramics were fabricated and their mid-infrared emission properties (the 5 I 6 → 5 I 7 transition) were studied at room- and cryogenic-temperatures with the goal of developing novel materials for 3-μm lasers.

A method for preparation of dense Y2O3-MgO composite ceramics by the microwave sintering was developed. The initial powders were obtained by glycine-nitrate self-propagating high-temperature synthesis (SHS) with different oxidant-to-fuel ratio. Density and IR-transmission of microwave sintered Y2O3-MgO ceramics increase with respect to dispersity of the SHS-powders and reach its maximum values for the powder prepared in a 20% fuel excess. The sintering behavior of Y2O3-MgO compacts was investigated by optical dilatometry and measuring an electric conductivity upon heating. Significant microwave radiation power surges at temperatures of 900-1000 degrees C, caused by the decomposition of magnesium carbonate, have been found. As a result of matching the conditions for the synthesis of powders and sintering modes, a transmission of composite ceramics of 78% at a wavelength of 6 mu m was achieved at a maximum processing temperature of 1500 degrees C.

The hot isostatic pressing of zinc sulfide, obtained by chemical vapor deposition technology, are studied to improve its quality characteristics. As a result of the studies carried out in the visible and near IR regions of the spectrum, the transmission of the treated samples was increased by 6-7 times compared to the untreated ones. In the wavelength range of 3-10 μm, the light transmission of the treated samples reached the theoretical limit. Keywords: chalcogenides, zinc sulfide, chemical vapor deposition, hot isostatic pressing.

Transparent ceramics based on thulium-doped cubic gadolinia Gd2O3 and its solidsolutions (Gd,Y)2O3, (Gd,Lu)2O3 and (Gd,Y,Lu)2O3 are fabricated by hot pressing. They feature low phonon energies and broad and smooth gain profiles extending above 2 μm.