Gamma-ray bursts from evaporating primordial black holes

It is believed that the detection of gamma-ray bursts from evaporating primordial black holes is highly improbable in the near future since the expected photon flux, consisting mainly of photons with energies ≳ GeV, is too low. Contrary to this point of view, we show that a large fraction of the black hole power at the final stage of evaporation (the last 10³ s) can be liberated as a burst of soft γ-ray emission of duration 10⁻¹–10³ s and luminosity 10²⁸–10³¹ erg/s in the energy range 0.1–1 MeV. According to our calculations of the black hole evaporation rate (within the Standard Model of elementary particles), when the black hole temperature exceeds approximately 10 GeV, the charged particle outflow from a black hole forms a well-defined plasma and can be described in the hydrodynamic approximation. In this case more than half of the rest energy of a black hole can be converted into soft gamma-rays due to the presence of the magnetic field with energy density comparable to that of charged particles. We consider various mechanisms leading to such transformation and estimate their efficiency. It is shown that, at least, some of the gamma-ray bursts detected by BATSE can be associated with evaporating black holes. Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 1, pp. 36–45, January, 1998.     

Mikrochemie

Ohne Zusammenfassung     

The vaporization of a metallic target by a microsecond pulsed TE-CO2 laser radiation

The analysis of some new experimental data has proved that the evaporation of a stainless steel target in vacuum under the action of powerful TE-CO₂ microsecond pulsed laser radiation is initiated on the initial spike or not at all. The minimum “tail” duration to get evaporation was deduced as a function of the temporal pulse shape characteristics and the metal thermophysical properties. The vaporisation process was accompanied by nonequilibrium heating of vapour clouds leading to the target surface shielding. Two self-regulated evolutions were recognised which were attributed to the intense vaporisation and the target evaporation by the UV plasma emitted radiation, respectively.     

The effect of LH wave on the peripheral plasma of TM-1-MH tokamak

The work is devoted to the study of the LH wave effect on the peripheral plasma of the TM-1-MH tokamak. The observed enhancement of the ion saturated current in the limiter shadow is interpreted as heating of the peripheral ions by absorption of decay waves generated in this region due to the nonlinear wave-plasma interaction.     

CO2 laser-induced plasma CVD synthesis of diamond

2 laser maintenance of a stationary optical discharge in a gas stream, exhausting over a substrate into the air (laser plasmatron). Nano- and polycrystalline-diamond films were deposited on tungsten substrates from atmospheric-pressure Xe(Ar):H₂:CH₄ gas mixtures at flow rates of 2 ?/min. A 2.5-kW CO₂ laser focused beam produced plasma. The deposition area was about 1 cm² and growth rates were up to 30–50 μm/h. Peculiarities and advantages of laser plasmatrons are discussed. Received: 15 January 1998/Accepted: 16 January 1998     

Change in Graphene Electronic Properties in the Presence of Acetone Vapor

Changes in properties of graphene grown by chemical vapor deposition (CVD) with water adsorbate removal from the graphene–SiO₂/Si substrate interface using an organic material, i.e., acetone, are studied. It is found that acetone vapor suppresses grapheme structuring under low-intensity nanosecond laser radiation (wavelength λ = 532 nm). It is found that the electron work function in graphene decreases by ～0.2 eV, which is presumably due to a decrease in the water adsorbate layer thickness at the mentioned interface.     

Laser nanoablation of graphite

Experimental data on laser ablation of highly oriented pyrolitic graphite by nanosecond pulsed UV ( $\lambda =193$  nm) and green ( $\lambda =532$  nm) lasers are presented. It was found that below graphite vaporization threshold $\approx $ 1 J/cm $^{2}$ , the nanoablation regime can be realized with material removal rates as low as 10 $^{-3}$  nm/pulse. The difference between physical (vaporization) and physical–chemical (heating + oxidation) ablation regimes is discussed. Special attention is paid to the influence of laser fluence and pulse number on ablation kinetics. Possibility of laser-induced graphite surface nanostructuring has been demonstrated. Combination of tightly focused laser beam and sharp tip of scanning probe microscope was applied to improve material nanoablation.     

Laser in micro and nanoprocessing of diamond materials

Basic processing operations will be presented. These include diamond polishing and shaping, production of conductive pathways, micro‐ and nanostructures on the diamond surface, such as diffractive optical elements. The possibility to laser produce conductive and hollow structures in the diamond bulk, including curved elements, will be demonstrated. Finally, the techniques of laser assisted diamond CVD, that allow production of smooth or selective‐area grown films will be presented     

Synthesis of carbon nanofibers and nanotubes in an activated-hydrogen reactor

The parameters of multilayer carbon nanotubes and nanofibers synthesized by pyrolysis of acetylene in a reactor filled with hydrogen activated by diffusion through a hot metallic wall, as well as synthesis products, are studied. The results of synthesis with catalysts applied on the substrate and in the gaseous phase are reported.