Frequency doubling and tripling in a Q-switched fiber laser

The frequency doubling and tripling in a Q-switched all-fiber laser are studied. It is demonstrated that the main limitations on the efficiency of the harmonic generation are related to the random polarization that is nonuniform with respect to axes, the asymmetric pulse shape with a flat trailing edge, and the significant spectral broadening of the multimode radiation of the fiber master oscillator in the fiber amplifier. The methods to increase the efficiency are proposed. For an IR pulse energy of about 0.3 mJ, duration of about 40 ns, and repetition rate of 1 kHz, the second- and third-harmonic pulse energies are greater than 60 and about 10 μJ, respectively.     

Luminescence of transparent glass ceramics containing Er<Superscript>3+</Superscript> and Yb<Superscript>3+</Superscript> zirconate-titanate nanocrystals

Luminescence regularities have been studied in new erbium/ytterbium materials based on glasses and glass ceramics of a magnesium-aluminosilicate system containing nanoscale erbium/ytterbium zirconate titanate crystals with the pyrochlore structure. Lifetimes of Yb³⁺ and Er³⁺ ions in the ² F_5/2 state and in the ⁴I_11/2 and ⁴I_13/2 states, respectively, and the efficiency of Yb³⁺ → Er³⁺ energy transfer have been evaluated. The identified spectral-luminescent characteristics of the studied glasses and glass ceramics co-doped with erbium and ytterbium ions show that these materials are promising media for producing laser generation in the spectral range around 1.5 μm.     

Nanodipoles of partial disclinations as carriers of non-crystallographic shear and crystal-lattice reorientation in nanocrystalline nickel and vanadium

Using electron microscopy, an investigation is performed of microstructure features of re-orientation microbands formed in nickel and V–4Ti–4Cr alloys under severe plastic deformation in the Bridgman anvils. It is shown that their formation could be described within the framework of a quasi-elastic mechanism of motion of partial-disclination dipoles, which is controlled by the flows of non-equilibrium point defects in the fields of local gradients of normal stress-tensor components. Operation of this mechanism offers an additional advantage of nanostructuring the defect substructure during plastic deformation of metallic materials, followed by formation of the structure states wherein the nanocrystallites measure a few nanometers.     

Thermal conductivity of the PbGeO<Subscript>3</Subscript> and PbGe<Subscript>3</Subscript>O<Subscript>7</Subscript> glasses

This paper reports on a study of the thermal conductivity of the PbGeO₃ and PbGe₃O₇ glasses.     

Stabilization of solution of cauchy problem for a non-divergent parabolic equation

Conditions for stabilization of solution of Cauchy problem for a linear second-order parabolic equation in nondivergent form are studied.     

Synchronous reactions of free radical formation upon low-temperature chlorination of aromatic and olefinic hydrocarbons

The free radical formation in reactions of low-temperature (77–150 K) chlorination of monomers and phenols was studied by ESR and calorimetry. The schemes were suggested for multicentered synchronous reactions of radical formation in polymolecular complexes, whose initial composition was directly determined for the first time from the structure of the radicals formed and thermodynamic parameters of the total exothermic effect.     

On the Problem of the Stability of a Tangential Discontinuity Surface between Two Fluids

Theorems of theoretical mechanics are used as a basis for a physical interpretation of the instability of a tangential discontinuity in the presence of low viscosity.     

Methods of Wavebeam Phase Front Reconstruction Using Intensity Measurements

Two methods for phase front reconstruction of paraxial linear polarized wavebeams are presented. Both of them are based on wavebeam field intensity measurements. The first method requires a reference wavebeam with known characteristics. The second one allows phase reconstruction using only wavebeam intensity measurements in a few cross sections. The methods described are successfully applied in the millimeter range for wavebeam diagnostics in mode converters, transmission lines and antenna elements. Since the methods are based on general principles they may be used not only for microwaves investigation.     

An integral relation for tensor polynomials

We prove two lemmas and one theorem that allow integrating the product of an arbitrary number of unit vectors and the Legendre polynomials over a sphere of arbitrary radius. Such integral tensor products appear in solving inhomogeneous Helmholtz equations whose right-hand side is proportional to the product of a nonfixed number of unit vectors.