Formation of micro- and nanophases on sulfide mineral surfaces under the effect of nanosecond electromagnetic pulses

The gas outflow from nanosecond breakdown channels of sulfide minerals under high-power electromagnetic pulses is considered with regard to iron and sulfur vapor condensation. New experimental data on the structural and chemical transformations of sulfide mineral surfaces under nanosecond pulse action are reported.     

On the characteristic properties of oxidation of sulfide minerals exposed to nanosecond electromagnetic pulses

High-power nanosecond electromagnetic pulses cause changes in the chemical and phase surface composition of sulfide minerals (pyrrhotite and pentlandite) and their sorption, flotation, and chemical activities. The influence of the conditions and parameters of the electric-pulse effect on the change in the amount of elemental sulfur and iron oxide on the surface of mineral particles, as well as the concentration of iron and sulfoxide ions in the aqueous mineral suspension, has been studied. The parameters of preliminary pulsed treatment of pyrrhotite and pentlandite that lead to improvement of flotation separation of minerals have been determined.     

Changes in the surface phase composition of sulfide minerals upon irradiation by high-power nanosecond pulses

The effect of high-power (high-voltage) nanosecond pulses on the phase composition and chemical state of atoms of surface layers of sulfide minerals with different semiconductor properties (galenite, molybdenite, and sphalerite) is investigated by means of XPES. Common patterns and characteristic features of the structural phase transformations of sulfide surfaces under the pulsed energetic effect are the formation and growth of a surface layer by the nonstoichiometric sulfur-enriched sulfide phase and Zn and Mo oxides and hydroxides; the staged character of the transformation of sulfur atoms in the composition of galenite and sphalerite surface layers; and the stability of the chemical state of sulfur in the molybdenite composition and lead atoms in the galenite composition.     

Nonlinear optical properties of an azo-based dye irradiated by picosecond and nanosecond laser pulses

The nonlinear optical properties of an azo-based dye were investigated using Z-scan technique employing 38 ps pulses at 532 and 1064 nm, and 6 ns laser pulses at 532 nm. Large nonlinear absorption and nonlinear refraction were observed at both ps and ns 532 nm in the azoic dye. When excited at ps 1064 nm, this dye displayed a large two-photon absorption cross-section (σ₂=1810 GM). Meanwhile, the optical nonlinearity mechanism was discussed in terms of molecular structure, excitation wavelength, and pulse width.     

Photoinduced transformations in C60 films irradiated by femtosecond laser pulses

Photoinduced polymerization and photoinduced diffusion of molecular oxygen in thin C₆₀ films irradiated by femtosecond laser pulses are investigated. A comparison of the Raman scattering and absorbed energy spectra and the irradiation doses required to observe photopolymerization using continuous-wave radiation and femtosecond pulses shows that the efficiency of both photoinduced processes decreases considerably in the latter case. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 4, 320–325 (25 August 1998)     

On the field-emission properties of sulfide minerals under high-power nanosecond pulses

The mechanism of absorption of the energy of high-power electromagnetic nanosecond pulses due to the field emission from the surface of natural semiconductors is considered. The limitations and possibilities of implementing this mechanism in sulfide minerals (pyrite and arsenopyrite) are demonstrated.     

Generation and amplification of nanosecond pulses by iodine lasers

Results are reported of experimental investigations of high-power photodissociation iodine laser pumped by lamps and by radiation from high-current electric discharges. The basic parameters of the working medium, the parameters of both lamp-pumped and discharge-pumped lasers, and methods of shaping of a short pulse with diffraction directivity of the radiation are investigated. The possibility of effective amplification of a short pulse by an iodine amplifier pumped with an open high-current discharge is demonstrated. An iodine laser generating a pulse of duration I nsec, divergence 10^-4 rad, and energy 100 J at a contrast 10⁸ and 300 J at a contrast 10²–10³ is described.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva, Akademii Nauk SSSR, Vol. 125, 46–103, 1980.     

Structural phase transformations in tin-fullerite films

X-ray diffraction, scanning electron microscopy, electron probe x-ray spectrum microanalysis, and Auger-electron spectroscopy were used to study the variations in the structure and elemental and phase compositions of tin-fullerite films stored in air. A new phase Sn_xC₆₀, tin whiskers, and fullerite “flowers and petals” were found to form under internal compressive stresses.     

Subpicosecond photon echoes by using nanosecond laser pulses

Subpicosecond time resolutions have been obtained in photon echoes when a sample was excited by two nanosecond dye laser pulses with a smooth and broad spectrum. The dye laser was pumped by second harmonics of a Q-switched Nd:YAG laser, and the pulse width was 10 ns. The sample was 3% Nd³⁺-doped silicate glass, and the center frequency of the dye laser was tuned at 5910 Å on resonance with the ⁴I_{$\text{9}\text{2}$} ? ²G_{$\text{7}\text{2}$}, ⁴G_{$\text{5}\text{2}$} transition of Nd³⁺. The homogeneous transverse relaxation time T₂ was measured to be 91 ps at 10 K in agreement with the previous measurements by picosecond pulses.     

Structural features of the self-action dynamics of ultrashort electromagnetic pulses

Self-focusing dynamics of electromagnetic pulses of arbitrary duration is analyzed numerically and analytically. The wave-field evolution is considered by the wave equation in the reflectionless approximation under quite general assumptions about the dispersion of the medium. Methods for qualitative investigation of the self-focusing dynamics of quasimonochromatic radiation are generalized to the case of wave packets with the length of a few oscillation periods. In particular, sufficient conditions for collapse and many other integral relations are obtained by the momentum method. A self-similar-type transformation is used to show that new structural features are primarily associated with the nonlinear dispersion of the medium (with the dependence of the group velocity of a wave packet on its amplitude). Numerical analysis confirms that the self-focusing of radiation is preceded by an increase in the steepness of the longitudinal profile.     

Efficient generation of relativistic electrons in a target irradiated by a pair of femtosecond laser pulses with a nanosecond delay

It is shown experimentally that the mean energy of accelerated electrons generated by irradiating a dense target with a pair of 13-ns-delay femtosecond laser pulses forming radiation with an energy contrast of 100–500 and an intensity of about 10¹⁸ W/cm² increases significantly in comparison with the case of high contrast ～10⁶.     

Rayleigh scattering of nanosecond light pulses

The relation _t/_theory = (₁/)[–exp(–t/)], obtained by M. Skowronek and J. Alayli for Rayleigh scattering of light pulses, is experimentally investigated. Relative measurements of scattering are made in Ar and N₂ without taking into account instrumental effects. It is shown that the level of scattering in a gas medium is independent of the pulse duration t for a pulse with a wavelength of = 0.53 m in the range 2 ns t 30 ns.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 49–54, October, 1985.     

Structural phase transitions on stepped surfaces

We predict a new class of structural phase transitions which occur on a microscopic length scale on stepped surfaces. These include commensurate and incommensurate “step-step” transitions. They can occur either on clean equilibrium surfaces or can be adsorbate induced. We also present a Landau-Lifshitz classification of some of these structural phase transitions. Critical exponents characterizing these transitions can be experimentally determined by LEED measurements.     

Characteristic properties of ZnO random laser pumped by nanosecond pulses

Investigations of UV radiation spectra of powdered zinc oxide and its unordered film were conducted. The samples were pumped by 3-rd harmonics of the two-stage Nd:YAG-laser (λ=355 nm) with pulse duration ∼10 ns. Maximum density of energy of pumping pulses was about 150 mJ/cm². With some of our samples, we achieved lasing. The threshold values of the pumping energy density occurred higher than those under picosecond pumping approximately for one-two orders of magnitude. It was shown that the threshold of lasing and the character of lasing spectra depend on the morphology of particles forming a powder. The long-wavelength shift of the maximum of lasing spectra with a rise of the pumping was observed. It was interpreted as a result of participation of electron–hole plasma recombination in the process of lasing. A chaotic character of lasing spectra was observed and partially analyzed. PACS 42.55.Zz; 78.55.Et; 42.70.Hj