Volumetric Modification of Transparent Materials with Two-Color Laser Irradiation: Insight from Numerical Modeling.

Traditionally, single-color laser beams are used for material processing and modifications of optical, mechanical, conductive, and thermal properties of different materials. So far, there are a limited number of studies about the dual-wavelength laser irradiation of materials, which, however, indicate a strong enhancement in laser energy coupling to solid targets. Here, a theoretical study is reported that aimed at exploring the volumetric excitation of fused silica with dual-wavelength (800 nm and 400 nm) ultrashort laser pulses focused on the material's bulk.

Double-pulse-laser volumetric modification of fused silica: the effect of pulse delay on light propagation and energy deposition.

Volumetric modification of dielectrics by ultrashort laser pulses is a complex dynamic phenomenon involving material photoexcitation and associated nonlinear processes. To achieve control over modification, it is necessary to gain a deep insight into the dynamics of laser-excited processes that can be realized using double-laser-pulse experiments with different time separations supported by numerical simulations. In this paper, we apply this approach to investigate fused silica modification with femtosecond laser pulses that provides time-resolved information about the dynamic behavior of the laser-excited bandgap material.

Research on the Grinding Energy Density in a Jet Mill.

Raw materials are used in many industrial technologies. The raw material frequently has to be prepared as an intermediate with an appropriate particle size distribution, which requires the use of grinding. In grinding processes, energy consumption is a very important profitability criterion for the applied particular size reduction technology.

The formation and migration of non-equivalent oxygen vacancies in PrBaCoMO, where M = Fe, Co, Ni and Cu.

The ab initio calculated defect formation energies are used for assessment of high-temperature thermodynamic functions that govern the appearance of oxygen vacancies in PrBaCo2-xMxO6-δ, where M = Fe, Co, Ni and Cu. The free energy of oxygen vacancy formation is shown to depend on the dopant and total oxygen content in the cobaltite. The experimentally observed trend for the oxygen vacancy concentration to increase with the atomic number of 3d dopants from Fe to Cu is explained as a result of the decrease of bond strength.

Relaxation of highly excited carriers in wide-gap semiconductors.

The electron energy relaxation in semiconductors and insulators after high-level external excitation is analysed by a semi-classical approach based on a kinetic equation of the Boltzmann type. We show that the non-equilibrium distributions of electrons and holes have a customary Fermi-like shape with some effective temperature but also possess a high-energy non-Fermian 'tail'. The latter may extend deep into the conduction and valence bands while the Fermi-like component is localized within a small energy range just above the edge of the band gap.

Electron-phonon relaxation and excited electron distribution in zinc oxide and anatase.

We propose a first-principles method for evaluations of the time-dependent electron distribution function of excited electrons in the conduction band of semiconductors. The method takes into account the excitations of electrons by an external source and the relaxation to the bottom of the conduction band via electron-phonon coupling. The methods permit calculations of the non-equilibrium electron distribution function, the quasi-stationary distribution function with a steady-in-time source of light, the time of setting of the quasi-stationary distribution and the time of energy loss via relaxation to the bottom of the conduction band.

Ab initio approach to the excited electron dynamics in rutile and anatase TiO2.

The relaxation of excited electrons in the conduction band of titanium dioxide with the rutile and anatase structure is investigated by means of a first-principle method. The evaluations are based on the pseudo-potential plane-wave approach to the electronic band structure calculations, the density-functional perturbation theory for the calculations of phonons and electron-phonon interactions, and on the 'Fermi golden rule' for evaluations of the electron relaxation time and the energy loss time. We demonstrate two regimes of the electron relaxation.

Ultrafast magnon generation in an Fe film on Cu(100).

We report on a combined experimental and theoretical study of the spin-dependent relaxation processes in the electron system of an iron film on Cu(100). Spin-, time-, energy- and angle-resolved two-photon photoemission shows a strong characteristic dependence of the lifetime of photoexcited electrons on their spin and energy. Ab initio calculations as well as a many-body treatment corroborate that the observed properties are determined by relaxation processes involving magnon emission.

Raman-based geobarometry of ultrahigh-pressure metamorphic rocks: applications, problems, and perspectives.

Raman-based geobarometry has recently become increasingly popular because it is an elegant way to obtain information on peak metamorphic conditions or the entire pressure-temperature-time (P-T-t) path of metamorphic rocks, especially those formed under ultrahigh-pressure (UHP) conditions. However, several problems need to be solved to get reliable estimates of metamorphic conditions. In this paper we present some examples of difficulties which can arise during the Raman spectroscopy study of solid inclusions from ultrahigh-pressure metamorphic rocks.

[Experience in the use of therapeutic photomatrix equipment].

Currently available data on clinical use of therapeutic photomatrix systems (TPMS) used for irradiation of extensive body areas are summarized. A therapeutic photomatrix system is implemented as an array of visible of infrared light emitters. The problems of photomatrix equipment interaction with biological objects are discussed.

Lifetimes of excited electrons in Fe and Ni: first-principles GW and the T-matrix theory.

We present the results of an ab initio calculation of excited electron lifetimes in ferromagnetic materials which incorporates non-spin-flip and spin-flip processes within GW and T-matrix approaches. The method we develop is applied to low-energy electron excitations in Fe and Ni. It is found that the spin-wave generation in Fe essentially reduces the lifetimes of the spin-minority d states whereas the free-electron-like spin-minority states and all the spin-majority states are affected much less.

Ultrafast electron dynamics in metals.

During the last decade, significant progress has been achieved in the rapidly growing field of the dynamics of hot carriers in metals. Here we present an overview of the recent achievements in the theoretical understanding of electron dynamics in metals, and focus on the theoretical description of the inelastic lifetime of excited hot electrons. We outline theoretical formulations of the hot-electron lifetime that originates in the inelastic scattering of the excited quasiparticle with occupied states below the Fermi level of the solid.

Lifetimes of excited electrons in Fe and Ni: first-principles GW and the T-matrix theory.

We present the results of an ab initio calculation of excited electron lifetimes in ferromagnetic materials which incorporates non-spin-flip and spin-flip processes within GW and T-matrix approaches. The method we develop is applied to low-energy electron excitations in Fe and Ni. It is found that the spin-wave generation in Fe essentially reduces the lifetimes of the spin-minority d states whereas the free-electron-like spin-minority states and all the spin-majority states are affected much less.

[Prostaglandin E in acute viral hepatitis].

Prostaglandin E levels were measured in the blood of 47 patients with acute viral hepatitis B (VHB), 17 patients with viral hepatitis A (VHA) and 15 healthy donors. Radioimmunoassay determined HBsAg concentrations in VHB patients' serum. Compared to the donors, prostaglandin E levels lowered significantly in VHB, but insignificantly in VHA.

[Lyophilized membranes as a test system for analyzing the properties of neuromediator receptors and activity of neurotropic agents].

The effect of lyophilization and prolonged storage of rat brain membrane preparations on the properties of receptors of cholinergic and adrenergic neuromediator systems has been studied by the radioreceptor assay. Lyophilized membrane preparations have been shown to be highly stable as compared with fresh membranes and retain their binding properties during storage for 1 year.