Yu. L. Kopylov

YAG and Y2O3 laser ceramics from nonagglomerated nanopowders

Undoped and Nd- or Yb-doped laser-grade yttrium aluminum garnet and (Y,La)2O3 ceramics with a transmittance above 80% in the 1-μm lasing region have been prepared by solid-state reactions using nonagglomerated Y2O3 and Al2O3 nanopowders. The Y2O3 nanopowders were prepared via laser evaporation, chemical precipitation from urea solutions, and grinding of commercially available Y2O3 in a purposedesigned laboratory-scale attritor at stirrer rotation rates of up to 1500 rpm. The YAG ceramics were prepared using commercially available Al2O3. After grinding, all of the powders had a particle size on the order of a hundred nanometers. Green compacts produced from the nanopowders were sintered in a vacuum furnace between 1615 and 1750°C to give highly transparent ceramic samples.

Nd3+:Y3Al5O12 laser ceramics: Influence of the size of yttrium oxide particles on sintering

The influence of the size of Y2O3 powder particles on the structure formation and densification of Nd3+:Y3Al5O12 laser ceramics has been studied. It is shown that the use of 50- and 100-nm yttrium oxide particles makes it possible to synthesize single-phase yttrium aluminum garnet at temperatures of 1200 and 1500°C, respectively, whereas in the case of 5000-nm yttrium oxide particles 2-h exposure at a temperature of 1500°C yields only 80 wt % of the Nd3+:Y3Al5O12 phase. Bulk swelling of pressed samples during sintering of 2.94Y2O3-0.06Nd2O3-5Al2O3 powders with the size ratio of the initial particles R(Al2O3/Y2O3) ∼ 5 is observed. The application of different-sized powders (R ∼ 2.5) provides quantitative ratios between phases in the 3Y2O3-5Al2O3 system at which shrinkage in a temperature range of 20–1500°C is dominant. Laser ceramics 0–2 at % Nd3+:Y3Al5O12 have been obtained by the solid-phase sintering of oxide powders (R ∼ 2.5). The slope efficiency for 1 at % Nd3+:Y3Al5O12 laser ceramics is found to be 33%.

Two-micron lasing on diode-pumped Y2O3 : Tm ceramics

The results of investigation of the spectral, luminescent and lasing properties of Tm : Y2O3 ceramics are presented. Lasing in Y2O3 ceramics is obtained at wavelengths of 1.95 and 2.05 μm. The maximum output laser power at these wavelengths was 2.4 and 0.3 W, respectively.

Bulk and surface contributions to the second-harmonic generation in tetra-aminodiphenyl films

The second-harmonic generation in thin (from 430 to 2330 nm) tetra-aminodiphenyl films obtained by thermal evaporation in vacuum is investigated. The dependences of the quadratic optical susceptibility on the film thickness are analyzed for several models assuming different location of nonlinear sources. The film nonlinearity is shown to have a bulk character.

Superlattice ZnSxSe1−x/ZnSySe1−y on (100) GaAs obtained by a photoassistant metal-organic chemical vapour deposition method

Abstract The influence of radiation in the visible spectral range on the growth rate and composition of ZnSxSe1−x during the usual metal-organic chemical vapour deposition process was observed. This fact was used to grow the superlattice under pulse radiation from a xenon or tungsten lamp directed at a GaAs substrate. Superlattices with periods of 60–1500 A were obtained by this method.

Laser-quality oxide Y3Al5O12 ceramics. Comparative studies of its basic characteristics and laser ceramics of a known manufacturer

The effect of sintering aids of SiO2, ZrO2, B2O3, and MgO oxides on the optimum sintering temperature, ceramics grain growth, total volume of residual pores, and optical quality of obtained ceramics is studied. The best combinations of sintering aids are found; as a result, YAG:Nd (1 at%) samples of ceramics of high optical quality are obtained. An original method for characterizing laser properties of ceramics is developed. Comparative measurements of main laser characteristics of the obtained ceramics and ceramics of the Konoshima Chemical Corp. Ltd wellknown in the world practice, are performed.

Algorithm for Elimination of Structural Noise in an Image Intensifier with Pyroelectric Array

Signal formation in image intensifier with pyroelectric array is considered. Application of panning regime is substantiated, and impossibility of image obturation is shown. A method for processing of thermal image is proposed to eliminate structural noise and allow operation in the absence of shutter. The method is optimized for pyroelectric arrays and practical applications are presented. Development of the method, in particular, with the aid of calibration of the signal of pyroelectric array is considered.

Optical properties and high-efficiency lasing of Nd:YAG and Ho:YAG ceramics

We report on optical properties and high-efficiency lasing of YAG ceramics synthesized at IREE (Fryazino) and IEP (Ekaterinburg). The best slope efficiency is to be 36% for 1%Nd:YAG ceramics and 40% for 1%Ho:YAG ceramics, in the latter case the emission was centered at 2090 nm. Internal losses in domestic ceramics prove to be a few percents per centimeter.

Specific features of thermal phonon scattering and ferromagnetic properties of ZnO varistor ceramics

The scattering of thermal phonons (T = 2.3–3.8 K) in ZnO single crystals and related 97.5ZnO + 0.5Bi2O3 + 0.5Co3O4 + 0.5MnO2 + 1Sb2O3 (mol %) ceramics has been studied. It is established that the transport characteristics of phonons with thermal frequencies in ceramics at liquid-helium temperatures are determined by the presence of Co2+ ions in ZnO grains. A model of phonon transport in ZnO-based ceramics is proposed that takes into account the electron states of cobalt. The energy of the corresponding level is estimated at Δ ≈ 5 K. Manifestations of the ferromagnetic effect are revealed.

Nanopowders M{sub 2}O{sub 3} (M = Y, La, Yb, Nd) with spherical particles and laser ceramics based on them

We have considered the problems of agglomeration of yttrium aluminium garnet (YAG) nanopowders prepared by chemical co-precipitation of precursors from aqueous solutions and subsequent calcination. To fabricate YAG and Y2O3 laser ceramic samples with high optical transmittance and reproducible characteristics, we have developed a method for producing non-agglomerated nanopowders of pure and doped Y2O3 by homogeneous chemical precipitation. Nanopowders Y2O3 with La and Yb as well as mixtures of Y2O3 : Nd and several commercial nanopowders of aluminium oxide have been compacted; optimised compacting technique have been selected; ceramic samples (Y, La, Yb)2O3 and YAG : Nd with high optical transmittance at a wavelength of 1 mm have been produced by solid-phase synthesis.