I. G. Murusidze

Relativistic wake-field generation by an intense laser pulse in a plasma

Abstract Generation of nonlinear plasma oscillations by an intense laser pulse is considered. It is shown that longitudinal plasma waves with relativistic amplitudes and phase velocities close to the speed of light c can be excited in the wake of a strong single laser pulse in a cold plasma. An analytical and numerical study of the relativistic wake-field generation by laser pulses with realistic shapes is carried out. A nonlinear scheme of the laser wake-field accelerator is suggested.

Dynamics of space-time self-focusing of a femtosecond relativistic laser pulse in an underdense plasma

The propagation of femtosecond, multiterawatt, relativistic laser pulses in a transparent plasma is studied. The spatio-temporal dynamics of ultrashort, high-power laser pulses in underdense plasmas differs dramatically from that of long laser beams. We present the results of numerical studies of these dynamics within a model which systematically incorporates finite pulse length effects (i.e., dispersion) along with diffraction and nonlinear refraction in a strongly nonlinear, relativistic regime. New space-time patterns of self-compression, self-focusing and self-phase-modulation, typical of ultrashort, high-intensity laser pulses, are analyzed. The parameters of our numerical simulations correspond to a new class of high-peak-power (> 100 TW), ultrashort-pulsed laser systems, producing pulses with a duration in the 10 - 20 femtosecond range. Spatiotemporal dynamics of these self-effects and underlying physical mechanisms are discussed.

Interaction of a non-symmetric powerful laser pulse with a plasma

The interaction of a powerful non-symmetric laser pulse with a plasma is studied. The non-symmetry is manifested in an abrupt cut-off of the rear edge of the laser pulse compared with its leading edge. At the same time, three qualitatively different regions are distinguished: the leading edge, the rear edge and the region behind the pulse, where it leaves a wake in the form of generated fields. An analytical solution has been found that defines the longitudinal accelerating field at the end of the rear edge. The results of numerical calculations confirm our physical point of view that the non-symmetry of the laser pulse increases the duration of the ion channel behind the front, thereby enhancing the focusing and effective acceleration of electron bunches.

GOLD AND SILVER NANOPARTICLES IN Spirulina platensis BIOMASS FOR MEDICAL APPLICATION

Abstract The synthesis of gold and silver nanoparticles by the blue-green algae Spirulina platensis for medical purposes was studied. A complex of optical and analytical methods was used in order to characterize produced nanoparticles. It was shown that the extracellular formation of metal nanoparticles of spherical shape with sizes in the range between 8 and 40 nm (the average size of 20-30 nm) takes place. The characteristics of gold and silver nanoparticles in the Spirulina biomass were compared. The role of biosorption processes in the synthesis of nanoparticles was estimated by using equilibrium dialysis. A positive influence of sonication on the process of microbial synthesis and yield of nanoparticles were demonstrated. The neutron activation analysis and the atomic absorption spectrometry were applied for characterizing the dynamics of gold and silver nanoparticles formation in the Spirulina platensis biomass. The neutron activation analysis was used for studying the elemental content of the Spirulina platensis biomass. Abstrakt Zbadano syntezę nanocząstek złota i srebra przez niebieskozielone glony Spirulina platensis, które są wykorzystywane do celów medycznych. Do scharakteryzowania wytworzonych nanocząstek zastosowano szereg metod optycznych i analitycznych. Wykazano, że zachodzi tworzenie pozakomórkowej, sferycznej nanocząstki o rozmiarach w zakresie od 8 do 40 nm (średnia wielkość 20-30 nm). Porównano charakterystyki nanocząstek złota i srebra wytworzonych w biomasie Spiruliny. Do oceny roli procesów biosorpcji w syntezie nanocząstek wykorzystano dializy równowagowe. Wykazano pozytywny wpływ ultradźwięków na procesy mikrobiologiczne i na wydajność syntezy nanocząstek. Do określenia dynamiki tworzenia nanocząsteczek złota i srebra w biomasie Spirulina platensis zastosowano neutronową analizę aktywacyjną i spektrometrię absorpcji atomowej. Stężenia pierwiastków w biomasie Spirulina platensis określono za pomocą neutronowej analizy aktywacyjnej

Spatiotemporal self-focusing and splitting of a femtosecond, multiterawatt, relativistic laser pulse in an underdense plasma

The dynamics of ultrashort, high-power laser pulses in underdense plasmas differs dramatically from that of long laser beams. We present the results of numerical studies of this dynamics within a model, which systematically incorporates finite pulse length (i.e., dispersion) effects along with diffraction and nonlinear refraction in a strongly nonlinear relativistic regime. New spatio-temporal patterns of self-compression and self-focusing typical of ultrashort high-intensity laser pulses are analyzed. The parameters of our numerical simulations correspond to a new class of high-peak-power (⩾100 TW), ultrashort-pulsed laser systems, producing pulses with a duration in the 10–20 femtosecond range.

Effect of concentrated light on morphology and vibrational properties of boron and tantalum mixtures

Heating a mixture of boron (impurities: carbon ∼ B50C2, boric acid – H3BO3) and tantalum (Ta) powders in nitrogen flow in a xenon high-flux optical furnace was performed. As-received powder composed of h-BN, H3BO3, TaB2, B9H11 and a number of other phases including β-rhombohedral boron, apparently, heavily doped with Ta. FT–IR examination of any sample of the material reveals the complicated vibration spectrum containing, in particular, an absorption band near 2260 cm−1. The shapes of these bands are different for samples because powders were synthesized at different temperatures. Known, that in β-rhombohedral boron lattice, there are nano-sized voids of different types, which allow an accommodation of single atoms or small groups of atoms. Theoretical calculations performed by the method of quasi-classical type yields the same value, 2260 cm−1, for the vibrations frequency of Ta atoms in D-type crystallographic voids in β-rhombohedral boron lattice. Since, Ta atoms are known to prefer accommodation just in D-voids the experimentally detected bands can be identified with localized vibrations of Ta atoms.

Self-Gompression and Self-Focusing Instability of Femtosecond Multiterawatt Laser Pulses in Underdense Plasmas

Self‐compression and self‐focusing instabilities of femtosecond, multiterawatt laser pulses propagating at subrelativistic intensities in strongly undercritical plasmas are studied. Our numerical simulations show that the spatiotemporal self‐compression works effectively in underdense (1% of the critical density) plasmas and relativistically intense, few‐cycle laser pulses can be produced in this way over propagation distances less than 2 mm. We found that pulses with Gaussian radial and time profiles are very robust maintaining their initial shape and proportions during this process, while, in general, the interplay between the self‐compression and the self‐focusing has proved to be very sensitive to the shape of laser pulses.