Nonlinear optical response of silver and copper nanoparticles in the near-ultraviolet spectral range

The nonlinear optical response of silver and copper nanoparticles synthesized by ion implantation in silica glasses is studied in the near-ultraviolet spectral range at a wavelength of 354.7 nm. The real and imaginary parts of the third-order nonlinear susceptibility χ⁽³⁾ of composite materials are measured. It is shown that the quantity Imχ⁽³⁾ is due to saturated absorption, while Reχ⁽³⁾ is due to the self-defocusing effect in composite materials.     

Ionization self-compression of intense femtosecond pulses propagating through gas-filled dielectric capillaries

A mechanism of the ionization-induced self-compression of femtosecond laser pulses propagating in a gas-filled hollow dielectric capillary has been investigated both experimentally and theoretically. In particular, the double self-compression of a laser pulse from 76 to 40 fs has been experimentally demonstrated. A theoretical model that explains the mechanism of such a self-compression and provides a good agreement with the experimental data has been developed. The model also predicts that a laser pulse shorter than 10 fs can be generated in the optimal regime with an energy efficiency exceeding the efficiency of self-compression on a filament widely discussed at present.     

Well-known perovskites (cerates, cuprates, manganates): Problems and facts; A review of nontraditional approaches

Phenomena and processes either new or not studied in-depth occurring in perovskite oxides and in systems which contain these compounds are reported and summarized. The materials under consideration are well-known for specific properties, e.g., cerates of alkaline earths are high-temperature proton conductors, manganates are electrode materials of SOFCs and show the effect of colossal magnetoresistance or YBa₂Cu₃O₇ cuprates YBa₂Cu₃O₇ are “high-temperature” superconductors. The presented nontraditional approach consists of considering physical and chemical phenomena and processes, which do not relate to the indicated main properties of the compounds. For instance, BaCeO₃ undoped and slightly doped has partially cerium in the form of Ce⁺³, which provides the effect of blue luminescence which is controlled by thermochemical treatment; H₂YBa₂Cu₃O₇ manifests mixed proton-electron conduction at 400–550 K under water vapor of 100–300 Pa; La_0.67Ca_0,33MnO_2.84 can dissolve some part of water vapor as this occurs in traditional HTPC. The electrochemical cells Pd | HTPC | hydrocuprate | HTPC | Pd and the more simple one Pd | HTPC | Pd show e.m.f. values near 1 V under certain conditions after polarization by d.c. currents at 420–520 K under different atmospheres. The system water vapor — membrane of undoped BaCeO₃-hydride is described. Defect chemistry equations are used to describe some of the phenomena which are employed for the production and storage of pure hydrogen.     

Laser pulse amplification upon Raman backscattering in plasma produced in dielectric capillaries

Femtosecond-pulse amplification upon stimulated Raman scattering is experimentally demonstrated for the case of a counter-propagating femtosecond laser pulse and a frequency-modulated broadband pump pulse with the same carrier frequency in a dielectric capillary filled with gas plasma. A value of ～10³ obtained for the spectral intensity amplification and ～10² for the output energy are the highest ever achieved for these quantities to date. Numerical simulation demonstrates good agreement with the experimental results. Based on the experimental data and the results of theoretical calculations, we propose a hydrodynamic mechanism for plasma-wave breaking as the mechanism playing an important role in the amplification restriction in the scheme considered.     

Power broadening of a diffusion resonance

We derive an expression in terms of cylinder functions for the shape of a nonlinear resonance in a two-level system with a rapidly decaying level. We show that when the natural linewidth is negligible, the square of the total width is the sum of squares of the power and diffusion widths. The traditional variational approximation yields a correct value for the full width at half maximum, but distorts the line profile. We derive a formula for the absorbed power as a function of the incident wave intensity for comparable power and diffusion broadening. The formula is found to be valid for a power width that is small or large compared to the diffusion width, and in a new intermediate domain where homogeneous saturation becomes inhomogeneous. Zh. éksp. Teor. Fiz. 113, 1632–1648 (May 1998)     

Reaction of 2-(2-oxo-2-arylethylidene)-2,3-dihydropyrimidine-4(1H)-ones with aldehydes

2-(2-Oxo-2-arylethylidene)-2,3-dihydropyrimidine-4(1H)-ones react with aromatic and heteroaromatic aldehydes to form the unsaturated ketones, whereas in the case of 3- and 4-benzaldehydes the corresponding trans-2-styrylpyrimidine-4(3H)-ones were obtained. A possible mechanism of hydrolytic cleavage of the product of condensation of 2-(2-oxo-2-phenylethylidene)-2,3-dihydropyrimidine-4(1H)-one with paraformaldehyde under acid catalysis and mechanochemical activation has been discussed.     

EPR of trivalent iron ions in a LiCaAlF6 crystal

The orientational dependences of the EPR spectra of Fe³⁺-doped LiCaAlF₆ single crystals (space group P31c, Z=2), grown at the Laboratory of Magnetic Radio Spectroscopy at Kazan’ State University, have been investigated in detail. The spectrum is described by a trigonal spin Hamiltonian with the following parameters: B ₂₀=40.072×10⁻⁴ cm⁻¹, B ₄₀=−5.799×10⁻⁴ cm⁻¹, B ₄₃=−4.281×10⁻⁴ cm⁻¹, A _s=24.33±1, A _p=6.13±1, g _∥=g _⊥=2.00217±0.0003. A theoretical calculation of the hyperfine structure parameters shows that they are described quite well when allowance is made for the overlapping of the wave functions of the paramagnetic center and the ligands (F⁻). Fiz. Tverd. Tela (St. Petersburg) 39, 488–490 (March 1997)