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. It is shown that the laser-generated free-electron plasma causes a shielding effect for the following pulse with a characteristic duration of ∼600 fs after the pulse action. Within this time interval, the second pulse produces a reduced modification as compared to a longer time separation between pulses. For double pulses with different energies, it was found that the volumetric modification is stronger when a lower-energy pulse couples with material first. This is explained by the combination of the effects of the re-excitation of self-trapped excitons, which are generated as a result of free electron recombination and associated light shielding. Experimental results are supported by numerical simulations of double laser pulse propagation in nonlinear media based on Maxwell's equations. Our findings offer a route for better controlling the inscription of 3D photonic structures in bulk optical materials.

The formation and migration of non-equivalent oxygen vacancies in PrBaCo2-xMxO6-δ, 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. The preferable location of oxygen vacancies near impurity atoms is accompanied by an anisotropic redistribution of electronic charge density. The most pronounced development of this effect in the case of iron doping leads to a low probability of tetrahedrally coordinated iron to exist in the layered cobaltites. It is shown that the calculated enthalpies of defect formation satisfactorily explain the experimentally observed changes of oxygen non-stoichiometry in the doped cobaltite. The energy barriers for oxygen jumps are found to vary only weakly at the doping thus suggesting rather insignificant dependence of the oxygen ion conductivity on 3d dopant nature. The earlier findings and results in the present work are indicative of promising properties combination in PrBaCo2-xNixO6-δ for the application as an electrode material in IT-SOFCs.

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. The effective temperature, effective chemical potential, and the shape of the high-energy component are governed by the process of electron-phonon interactions as well as by the rates of carrier generation and inter-band radiative recombination.

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. The actual calculations have been performed for titanium dioxide in the anatase structure and zinc oxide in the wurtzite structure. We find that the quasi-stationary electron distribution function has a peak near the bottom of the conduction band and a tail whose maximum energy rises linearly with increasing energy of excitation. The calculations demonstrate that the relaxation of excited electrons and the setting of the quasi-stationary distribution occur within a time of no more than 500 fs for ZnO and 100 fs for anatase. We also discuss the applicability of the effective phonon model to energy-independent electron-phonon transition probability. We find that the model only reproduces the trends in the change of the characteristic times whereas the precision of such calculations is not high. The rate of energy transfer to phonons at the quasi-stationary electron distribution also have been evaluated and the effect of this transfer on the photocatalysis has been discussed. We found that for ZnO this rate is about five times less than in anatase.

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. Thereby we demonstrate that magnon emission by hot electrons occurs on the femtosecond time scale and thus provides a significant source of ultrafast spin-flip processes. Furthermore, engineering of the magnon spectrum paves the way for tuning the dynamic properties of magnetic materials.

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. For the excited electrons with energy less than 0.01 eV above the conduction band bottom the relaxation occurs in the pico-second timescale, whereas at higher excitation energies the electron relaxation time is within a few femto-seconds and the energy loss time is within a few tens of femto-seconds.

[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. The main results of the clinical use of photomatrix equipment for treatment of a number of diseases are considered. Four main variants of clinical application of photomatrix equipment are considered: use of TPMS alone; use of TPMS in combination with medicamentous treatment; use of TPMS in combination with other physiotherapeutic procedures; use of TPMS in combination with other physiotherapeutic procedures and medicamentous treatment.

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. The influence of spin-flip scattering on the lifetimes in Ni appears to be weak. The T-matrix non-spin-flip processes are important for the lifetimes of excited spin-minority states.

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. The influence of spin-flip scattering on the lifetimes in Ni appears to be weak. The T-matrix non-spin-flip processes are important for the lifetimes of excited spin-minority states.

[Prostaglandin E in acute viral hepatitis]. / Prostaglandin E pri ostrykh virusnykh gepatitakh.

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. An inverse relationship occurred between prostaglandin E values in VHB and HBsAg concentrations.

[Lyophilized membranes as a test system for analyzing the properties of neuromediator receptors and activity of neurotropic agents]. / Liofilizovannye membrany kak test-sistema dlia analiza svoistv retseptorov neiromediatorov i aktivnosti neirotropnykh sredstv.

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.