Comparison of phase-aberrated laser beam quality criteria

With any form of phase distortions there is the need to qualitatively characterize beam quality. Three different qualitative criteria are most commonly used for this purpose, each of them describing the beam with one ratio: the overlapping integral, the Strehl ratio, and the M2 parameter. We have analyzed the interrelation of the above- mentioned criteria in the three most common types of beam quality degradation: thermal lens, electronic self-focusing, and spherical aberration. Approximate analytical expressions for all three criteria and three types of beam distortion are derived for Gaussian and super-Gaussian intensity profiles. The efficiency of characterizing those beams by various criteria is discussed.     

Interferometry based technique for intensity profile measurements of far IR beams

We present a novel, to the best of our knowledge, method for measuring the intensity profile of far-IR beams. The method is based on the measurements of nonstationary variation in optical thickness of a fused-silica plate heated by the studied radiation. The optical thickness is observed by means of a reflecting interferometer. Purpose-made experimental setup allows one to measure beams with an aperture of up to 60 mm with a spatial resolution of 1 mm. The accessibility of the utilized technologies and the possibility to easily increase the aperture are the major advantages of this approach. The probable area of application for the method is measurements of beams produced by powerful industrial far-IR lasers.     

Mechanical alloying of Ni3Al with molybdenum and arrangement of Mo atoms in sublattices of the intermetallic

Mechanochemical synthesis (MS) of Ni₇₀Al₂₅Mo₅ (composition 1) and Ni₇₅Al₂₀Mo₅ (composition 2) mixtures, in which 5 at % Mo substitutes for the equal amount of Ni or Al, leads to the formation of Ni-based nanocrystalline (coherent domains are ～7–12 nm in size) solid solutions; in this case, some amount of molybdenum remains free. A comparison of the lattice parameters of solid solutions, which were determined experimentally, with the magnitudes determined theoretically using Vegard law and Bozollo-Ferrante simulation, which takes into account volume modules of elasticity of elements, showed an increase in interactions between atoms composed the solid solution and the formation of regions characterized by short-range order. The heating of mechanically synthesized three-component Ni(Al, Mo) solid solutions to 720°C in a calorimeter chamber forms the ordered γ′ phase (L1₂) at T ～ 450°C. An analysis of the ratio of relative intensities of superlattice and fundamental reflections showed that, whatever the composition of initial mixture, Mo atoms always occupy positions in the Al sublattice. This arrangement of Mo atoms was confirmed by calculations of coefficients of concentrational variations of the lattice parameters. When molybdenum is added to Ni₃ Al, Mo atoms, rather than Ni atoms, complete the Al sublattice. In this case, vacancies compensate for the lack of atoms in the Ni sublattice.     

Effect of alloying on superplasticity of two-phase brasses

Superplasticity characteristics of two-component and multicomponent brasses in the temperature range 525–600°C have been investigated at tension tests under the conditions of stepwise enhancement in the strain rate and when maintaining a constant strain rate of 1 × 10^–3 s^–1. The effective energy for activating superplastic deformation has been determined. It has been shown that brass alloyed with aluminum, tin, and iron exhibits large elongations and less porosity due to superplastic deformation. Changes in the granular structure and sample surfaces have been analyzed after deformation, and signs of grain-boundary sliding and intragrain deformation have been revealed in the alloys studied.     

Low-temperature photoluminescence of heavy-ion-implanted InGaP solid solutions

The photoluminescence spectra of samples of the solid solution In(0.5)Ga(0.5)P before and after implantation of high-energy nitrogen ions to doses of 10¹¹−5×10¹² cm⁻² shows that the photoluminescence of the implanted (and annealed) samples may be the result of the formation of essentially one-dimensional semiconductor structures along the individual ion tracks. Pis’ma Zh. Tekh. Fiz. 24, 59–62 (September 12, 1998)     

Modulus of elasticity of some refractory compounds

Conclusions Measurements were made of the moduli of elasticity of nonporous refractory compounds prepared by the method of diffusion impregnation. The following values were obtained: 49,300±2000 kg/mm² for NbN, 58,700±2000 kg/mm² for TaN, 58,000±2000 kg/mm² for NbC, 65,000±2000 kg/mm² for NbB₂, 70,000±2000 kg/mm² for TaB₂, 68,500±2000 kg/mm² for Mo₂B₅, and 79,000±2000 kg/mm² for W₂B₅.Translated from Poroshkovaya Metallurgiya, No. 3 (63), pp. 32–33, March, 1968.     

Monolithically-integrated hybrid heterostructure diode laser with dielectric-film waveguide DBR

In the monolithically-integrated hybrid (MIH) DBR diode laser, the five-layer Ga(Al)As-GaAs heterostructure waveguide of the gain region was monolithically butt-joined on a common GaAs substrate with a highly-transparent corrugated dielectric-film waveguide consisting of sputtered SiO2, Ta2O5, and evaporated (corrugated) As2S3layers. The laser operated with the first-order grating under the pulsed current pumping at 300 K. The efficient resonant mode conversion (70 percent in power) has been obtained at the interface between the heterostructure and dielectric waveguides. The fundamental transverse and single-longitudinal mode output emission was obtained up to 160 mW (Ith = 120mA) with external differential quantum efficiencyeta simeq 32percent. The advantages of a dielectric-film waveguide DBR are demonstrated. The use of such a DBR results in a high degree of sidemode suppression and stability of the spectral position of the emission line under the temperature variation, the corresponding spectral shift beinglsim 0.01Å/K.     

Dependence of the properties of a carbon-aluminum composite material on its carbide phase content

Conclusions To ensure that the necessary bond strength at fiber/matrix interfaces is attained during the manufacture of a carbon-aluminum composite such as that investigated in this work, the degree of chemical reaction between the components must be strictly controlled, the optimum amount of the reaction product (Al₄C₃) being 2–3%. For matrices of other compositions and fibers of other types, the optimum Al₄C₃ content may be different. A bond at a fiber/matrix interface forms mainly as a result of mechanical joining of the components by carbide phase particles, which leads to the appearance at this interface of numerous micro-channels capable of acting as paths of mass (e.g., water) transport into the main volume of material.The corrosion of a carbon-aluminum composite material is a consequence of the occurrence of two processes — decomposition of the Al₄C₃ and anodic dissolution of the aluminum in contact with the carbon. The decomposition of the aluminum carbide weakens the bond between the components by increasing the volume of reaction products, which in turn mechanically damages the fibers and induces cracking in the matrix, i.e., intensifies crevice corrosion. The corrosion resistance of a carbon-aluminum composite can be enhanced on the one hand by decreasing the amount of the carbide phase without adversely affecting the strength of the bond between the components (e.g., by suitable choice of matrix composition and fiber type) and, on the other, by preventing electrical contact being made between the matrix and fibers. The most effective method of achieving both ends simultaneously is to use carbon fibers with protective coatings.Translated from Poroshkovaya Metallurgiya, No. 2(218), pp. 45–49, February, 1981.     

Heating-induced transformations of multicomponent alloys prepared by mechanochemical synthesis

Multicomponent (Cr, Fe, Co, Ni, Al, Ti, and Nb) powder alloys prepared by milling five- to seven-component equiatomic mixtures of elemental powders in a Fritsch (P-7) planetary mill have been characterized by differential thermal analysis and X-ray diffraction. The results demonstrate that, if the starting mixture contains Al, the BCC solid solution formed as a result of the milling undergoes heating-induced CsCl-type ordering (β-phase). If not only Al but also Ti are present in the starting mixture, further heating causes the β-phase to convert to an L2₁ phase with the composition (Ni,Co)TiAl. The elements Cr and Fe form a tetragonal σ-phase. The presence of Nb in the starting mixture suppresses the formation of the σ- phase and favors the formation of a hexagonal Laves phase of complex composition: (Fe,Co)CrNb.