Shaping of picosecond pulses for pumping optical parametric amplification

The use of temporally shaped pump pulses for optical parametric chirped-pulse amplification can increase the efficiency and suppress possible spectral distortions in this process. With this goal in mind a novel method for shaping narrowband picosecond pulses has been developed. The method is based on the pulse stacking principle, where replicas of the incoming pulse are created in a specially designed four-beam interferometer. The replicas are recombined with appropriate relative delays. The interferometer design allows for a unique flexibility in varying the pulse shape, since all relevant degrees of freedom, such as relative intensities and delays between the pulse replicas are independently adjustable. Here we describe the design of our device in detail and report on the experimental demonstration of its pulse-shaping capabilities. PACS 42.65.Yj; 42.65.Re; 42.81.Gs     

The geometrical form for the string space-time action

In the present article, we derive the space-time action of the bosonic string in terms of geometrical quantities. First, we study the space-time geometry felt by a probe bosonic string moving in antisymmetric and dilaton background fields. We show that the presence of the antisymmetric field leads to space-time torsion, and the presence of the dilaton field leads to space-time non-metricity. Using these results we obtain the integration measure for space-time with stringy non-metricity, requiring its preservation under parallel transport. We derive the Lagrangian depending on stringy curvature, torsion and non-metricity.     

Cavity effects in coiled coil IR reference source

We performed a high resolution imaging of a coiled coil filament used in tungsten lamps, a standard reference source in spectroscopy. The radiometric results using two-wavelength thermometry indicate that its configuration also introduces cavity effects and non-uniformity of filament temperature distribution, with the average temperature calculated to be 2869 K. Considering the tungsten source as an extended body, significant temperature variations of up to +19 K are found above its nominal 2850 K value.     

Creep strain recovery of Fe-Ni-B amorphous metallic ribbon

Creep strain recovery and structural relaxation of the amorphous metallic glass Fe₄₀Ni₄₁B₁₉ after longtime loading at different annealing temperatures below the glass transition temperature have been studied using anisothermal differential scanning calorimetry (DSC) and dilatometry (TMA). It has been demonstrated that structural relaxation effects depend on the stress-annealing temperature of the amorphous ribbon. The structural relaxation states of the amorphous ribbon annealed at different temperatures under and without applied stress have been compared. The activation energy spectra were calculated from the anisothermal dilatometric measurements using the modern method based on the Fourier transformation technique. The influence of the annealing temperature on the shape of creep strain recovery spectra has been analyzed.      

On the harmonic oscillator on the Lobachevsky plane

We introduce the harmonic oscillator on the Lobachevsky plane with the aid of the potential V (ϱ) = (a ² ω ²/4) sinh(ϱ/a)², where a is the curvature radius and ϱ is the geodesic distance from a chosen center. Thus, the potential is rotationally symmetric and unbounded, as in the Euclidean case. The eigenvalue equation leads to the differential equation of spheroidal functions. We provide a basic numerical analysis of eigenvalues and eigenfunctions provided that the value of the angular momentum, m, is equal to 0. Dedicated to the memory of V. A. Geyler     

Temperature dependence of the lowest frequency <Emphasis Type="BoldItalic">E</Emphasis><Subscript><Emphasis Type="Bold">g</Emphasis></Subscript> Raman mode in laser-synthesized anatase TiO<Subscript>2</Subscript> nanopowder

Nanosized titanium dioxide (TiO₂) powder was prepared by a laser-induced pyrolysis. Specific surface area of the as-grown powder measured by BET method was 109 m²/g. The grain size (14.5 nm) estimated from these data coincides well with the crystallite size (12.3 nm) determined by XRD measurements. The average grain size (∼35 nm) obtained from the subsequent SEM measurements refers to considerable agglomeration of nanoparticles. Raman spectroscopy has been used to investigate the structural properties of TiO₂ nanopowder and its anatase structure is confirmed. The blueshift and broadening of the lowest frequency E_g Raman mode at temperature range ∼25–550 K have been analyzed using a phonon-confinement model. Dominant influence of the strong anharmonic effect at higher temperatures was demonstrated. PACS 81.07.Wx; 78.30.-j; 63.22.+m     

Calculation of stopping power for partially stripped ions using an oscillator model

Collision of swift ions with atoms was considered in this paper. The projectile and target atoms were modeled as assemblies of quantum oscillators and it was assumed that both, target and projectile could be excited or ionized, without charge exchange. The model presented here is an extension of the one given by Sigmund and Haagerup [Phys. Rev. A 34, 892 (1986)]. The number of electrons bound to the projectile, as a function of the projectile velocity, was used from Cabrera-Trujillo et al. [Phys. Rev. A 55, 2864 (1997)]. Contributions to energy loss from excitation of the projectile and targets were separately considered. It has been found that projectile excitation contributes up to 20% to the total energy loss in the lower energy region. Comparisons with other authors, including SRIM 2003, are also given and good agreement was found.     

Self-organization of lamellae and permeability of microporous oriented polypropylene films

The effect of the annealing temperature T _ann of extruded polypropylene films on the structure of membranes prepared by the uniaxial extension of annealed films with the subsequent thermal fixation has been investigated using small-angle X-ray scattering and scanning electron microscopy. It has been shown that an increase in the permeability of membranes with increasing temperature T _ann is due to the self-organization of elements of the lamellar structure of the polymer as a result of the ordering and aggregation of particles.