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.     

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.     

Structural and phase transformations of sulfide mineral surfaces irradiated by nanosecond electromagnetic pulses

The effect of high-voltage nanosecond electromagnetic pulses on the phase composition of chalcopyrite and sphalerite surfaces is investigated by IR-Fourier spectroscopy, XPS, and UVS. Electromagnetic pulse treatment results in the formation and accumulation of copper and/or iron sulphates Me _x (SO₄) _y in superficial chalcopyrite layers, zinc sulphate ZnSO₃, and carbonate ZnCO₃ on sphalerite surfaces, changing their electrochemical and physicochemical properties; i.e., a rise in electrode potentials creates favorable conditions for anionic collector sorption and promotes sulfide flotation activity.     

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.     

Electrical breakdown in ionic crystals exposed to nanosecond pulses

Electrical breakdown in alkali halide crystals subjected to ∼10-ns-long electrical pulses is studied. Two, primary and basic, channels of the anodic discharge are noted. In the presence of the primary channel, the other arises at static breakdown voltages. Otherwise, the basic channel forms at voltages exceeding the static breakdown voltage by more than four times. The basic channel is assumed to form via a cascade of Auger transitions. The generation and migration of linear defects seem to play a significant role in the basic channel formation. The enhancement of the pulsed dielectric strength of the crystals is related to conditions of current passage through the metal-insulator interface.     

Energy concentration in electric discharges between particles of semiconducting sulfide minerals under the action of high-power nanosecond pulses

A model for development of electric discharges between particles of sulfide minerals (pyrite) under the action of high-voltage nanosecond pulses is proposed. It is shown that through discharges in a layer of pyrite particles lead to energy concentration in small contact regions between particles; the concentrated energy is sufficiently high for local decomposition (disintegration) of mineral complexes.     

Condensation of matter during gas outflow from nanosecond breakdown channels of sulfide minerals

The gas outflow from nanosecond breakdown channels of sulfide minerals under the effect of high-power electromagnetic pulses is considered, with allowance for the condensation of iron vapors. The condensation of matter in an outflowing jet is shown to be an effective mechanism for structural-chemical transformations of sulfide surfaces.     

Study of explosive boiling of transparent liquid on metal substrate exposed to nanosecond laser pulses

Preliminary experimental investigation of photoacoustic pressure signals induced by nanosecond laser pulses in aluminum targets contacting a water layer was performed. It was shown that for some laser intensities the signal has a two-peak structure. The first peak is due to the thermoelastic effect, while the other results from the explosive evaporation. At low intensities, only the first peak is observed. At sufficiently high intensities, the signal recovers the one-peak shape and becomes narrower as compared with the two-peak shape because of the rapid increase in evaporation pressure and earlier beginning of the explosive evaporation.     

Dynamic properties of bacteriorhodopsin exposed to ultrashort light pulses

Bacteriorhodopsin (BR) in its metastable form was used for pulsed holographic recording at lambda~400nm . It is shown that the properties of BR are insensitive to changes in the writing light's pulse width. When holograms are recorded in the BR stable form (lambda~600 nm) , the sensitivity of the medium and the diffraction efficiency of those holograms are reduced proportionally to the decrease in the light's pulse width.     

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     

The role of gas outflow from nanosecond breakdown channels in the electric-pulse discharge disintegration of sulfide minerals

The heated gas outflow from nanosecond breakdown channels of sulfide minerals (pyrite) under high-power electromagnetic pulses is considered. It is shown that the gas outflow from channels can be an additional destructive factor in the processes of the electric-pulse discharge disintegration of fine-disseminated mineral complexes.     

纳秒脉冲下几种液态介质绝缘性能的比对

利用自行研制的纳秒脉冲实验平台（输出脉冲前沿30 ns,半宽百纳秒）和标准介电强度测试仪,对变压器油、甘油、去离子水、Galden HT200四种液体绝缘介质在直流与纳秒脉冲下的击穿特性进行了实验研究与结果比对,结果表明：在直流与纳秒脉冲下,Galden HT200均具有最高的击穿场强,且两种情况下均比变压器油高出40%以上;纳秒脉冲下,Galden HT200与变压器油的击穿场强均提高6.5～7倍,Galden HT200击穿过程耗时最短（ns量级）,其次是变压器油（20 ns）,然后依次为甘油（45 ns）和去离子水（70 ns）;多次放电后,粘度系数最大的甘油更易在电极间隙处聚集碳化放电产物,粘度系数较小的Galden HT200和去离子水则无明显痕迹,但二者放电过程会产生明显的冲击波,多次放电后易造成间隙电极松动。

     

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.     

On compression of electromagnetic pulses in dielectric plates

The results of theoretical investigation of propagation of electromagnetic wave pulses in nonlinear dielectric plates, taking into account the dispersion introduced by the plate to the maximum possible extent, are presented. The investigation is aimed at obtaining the shortest possible pulses of electromagnetic waves. Pulse compression is based on the collapse of electromagnetic waves in transparent dielectrics with electronic non-linearity. The integral equation for describing the pulse compression is derived, and conditions under which a pulse is compressed relative to time and one of the transverse coordinates are determined. Numerical simulation shows that quite short (on the order of a few femtoseconds) pulses can be obtained in this way.     

On the propagation of electromagnetic pulses under the conditions of quasi-resonance

A theory of quasi-resonance for the model of atoms with an arbitrary number of levels is developed by the method of unitary transformation without recourse to Bloch’s equations. Corrections to the results known from the theory of adiabatic following, which refine these results and take into account dispersion of the nonlinear response of the resonant system, are obtained. The condition for quasi-resonance with a single atomic transition is shown to impose stringent limitations on the form of the nonlinear evolution equation for the electric field envelope of the pulse with dispersion of the nonlinear response taken into account, which prohibit the reduction of the equation indicated to familiar, fully integrable systems.     

Passive Q-switching and mode-locking for the generation of nanosecond to femtosecond pulses

The passive and hybrid Q-switching and mode-locking of solid-state lasers, dye lasers, semiconductor lasers and gas lasers is reviewed. The dynamics of saturable absorbers and reverse saturable absorbers is illustrated. The nanosecond pulse generation by passive and hybrid Q-switching of low-gain active media is described. The picosecond and femtosecond pulse generation by passive and hybrid mode-locking in low-gain and high-gain active media is analysed. The performance data of passively and hybridly mode-locked cw femtosecond dye lasers are collected. The pulse shortening of ultra-fast pulses with saturable absorbers in intra-cavity and extra-cavity configurations is discussed.     

Diagnosis of high-power nanosecond pulses of microwaves

This article surveys methods for measuring the amplitude, time, energy, spectrum, and structure of the wave field of powerful nanosecond pulses of electromagnetic radiation obtained from relativistic microwave sources. Institute for High-Power Electronics, Siberian Division of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 98–109, December, 1996.     

Wavelength conversion of nanosecond pulses to the mid-IR in photonic crystal fibers

We investigate degenerate four wave mixing with nanosecond pulses in fused silica photonic crystal fibers. Phase-matching curves are calculated taking into account the material and waveguide dispersion. Experiments with a nanosecond pulsed Nd:YAG pump laser and relatively short fiber lengths show more than an octave spanning conversion to idler and signal wavelengths at 3.105 μm and 0.642 μm, respectively. Conversion efficiency depends on the fiber length and pump intensity and is limited in our experiments by damage of the fiber input facet. Our results represent a new stretch towards the limit of the silica transmission window in the mid-infrared (IR).