Dynamics of high-temperature plasma formation during laser irradiation of three-dimensionally structured,low-density matter

Results are presented from an experimental investigation of the properties of the plasma produced by the action of a radiation pulse at the second harmonic of a Nd laser, with average intensity ~5·10¹⁴ W/cm² in the focal spot, on flat targets consisting of porous polypropylene (CH)_x with an average density of 0.02 g/cm³ (close to the critical plasma density) and with ~50 μm pores. The properties of the laser plasma obtained with porous and continuous targets are substantially different. The main differences are volume absorption of the laser radiation in the porous material and much larger spatial scales of energy transfer. The experimentally measured longitudinal ablation velocity in the porous material was equal to (1.5–3)·10⁷ cm/s, which corresponds to a mass velocity of (3–6)·10⁵ g/cm²· s, and the transverse (with respect to the direction of the laser beam) propagation velocity of the thermal wave was equal to ~(1–2) ·10⁷ cm/s. The spatial dimensions of the plasma plume were ~20–30μm. The plasma was localized in a 200–400μm region inside the target. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 7, 462–467 (10 October 1996)     

An automated high precision calorimeter for the temperature range 200K–400K. Part 1: Design and performance

A fully automated calorimeter has been designed and tested over the temperature range 200K–400K. The system may be used for measurements with an absolute accuracy of 0.2% of samples of approximate mass 50g and thermal capacity 15 JK⁻¹. The temperature of the sample is determined by a quartz crystal thermometer of resolution 100 μK which is not in direct thermal contact with the sample. The performance of the system is illustrated by results obtained on high purity copper, distilled water and K₂PbCu(NO₂)₆ which exhibits very sharp first order phase transitions at about 273.4K and 281.8K.     

Low noise SIS mixer for 230 GHz receivers of plateau de bure interferometer

We present a SIS mixer developed for 200 – 250 GHz band receivers of Plateau de Bure Interferometer. We demonstrate the minimum DSB receiver noise of 20 K at 220 GHz. The average receiver noise of 25 K is possible in 200 – 250 GHz range. The receiver conversion gain and output noise instability of 10⁻⁴ on the time scale of 1 minute is comparable with the Shottky receivers performance. The minimum measured SIS mixer noise of about 10 K is close to the quantum limit. The waveguide SIS mixer with a single backshort has two junction array with inductively tuned junctions. The Nb/Al Oxide/Nb SIS junctions are 2.24 μm² each with the Josephson critical current density of 3.2 KA/cm². The thermal properties of the SIS mixer are studied. The mixer band of the low noise operation is in a good agreement with the design requirements.     

Experimental observation of a two-phase state of expanding nuclear matter at E p=1 GeV

A double-arm time-of-flight spectrometer was used to study the thermal multifragmentation of ²³⁸U, ²³²Th, and ¹⁹⁷Au nuclei that is induced by 1-GeV protons. It is established that the pseudoevaporation channel, where a single heavy fragment of mean mass in the range 80–90 amu is produced in association with approximately ten smaller clusters (〈M〉=7–10 amu) emitted anisotropically at low velocities, is dominant at this energy. The pseudoevaporation cross sections change from 10±5 mb for ¹⁹⁷Au to ¹²⁰±40 μb for ²³⁸U. For ²³⁸U and ²³²Th, it is found that, in the region M<8 amu, the power law is violated, which is explained by the decay of part of small primary clusters in the course nucleon exchange through the “gas” phase within the expanding nucleus. __________ Translated from Yadernaya Fizika, Vol. 64, No. 8, 2001, pp. 1541–1550. Original Russian Text Copyright ? 2001 by Chestnov, Sokolovsky.     

In searches for daemons

A possibility is considered of detecting Planckian particles carrying an electric charge Z≈10 and supposedly forming the dark matter of the Galactic disk, whence they are captured by combined action of the Sun and the Earth into strongly elongated Earth-crossing orbits. The flux of such dark electric matter objects, daemons, at the Earth’s orbit may reach f _⊕≈3×10⁻⁷cm⁻²s⁻¹ at a velocity about 52 km/s. Negatively charged daemons are capable of catalyzing the fusion of light (Z _n<10) nuclei. The rate of capture (and fusion) of nuclei should be particularly high in a metallic phase. A detection system is described that consists of beryllium plates 45 mm thick and 1200 cm² in area coated with a ZnS(Ag) scintillator. It is assumed that the products of the fusion reaction 2⁹Be → ¹⁸O that are ejected in amounts of up to about 10⁴ from the points of daemon entrance and exit would give rise to scintillations with a delay of about 1μs. An exposure of the system for 300 h revealed no event. The reason for the negative result can be (1) too optimistic an estimate of the flux (the inclusion of some factors could lower it by 1.5–3 orders of magnitude) and (2) the poisoning of the catalyst by capture of nuclei with Z _n≥10. The time required for the recovery of the daemon catalytic properties is estimated from the analysis of the energy release in the Sun at no less than 3×10⁻⁷ s. The analysis of the total available data suggests that the daemon flux at the Earth is about 3×10⁻⁸ cm⁻² s⁻¹. The experiments will be continued. From Yadernaya Fizika, Vol. 63, No. 6, 2000, pp. 1112–1117. Original English Text Copyright ? 2000 by Drobyshevski. This article was submitted by the author in English.     

Dual-beam laser analyzer for inhomogeneities in active regions of multielement photodetectors

We describe equipment and a procedure for measuring inhomogeneities in active regions of solar cells, photoelectric transducers, and multielement photodetectors, based on a computer-controlled dual-beam laser scanner including a Pentium III personal computer, an HP-34401A digital multimeter with RS-232 serial interface;, a platform movable along the Y coordinate with the sample multielement photodetector to be tested and a microprobe device for picking up the photocurrents, an optical head with laser photodiodes in the visible (λ₁ = 0.68 μm) and IR (λ₂ = 0.82 μm) ranges scanning along the X coordinate, and a control unit for focusing the laser beams λ₁, λ₂, stabilizing the laser radiation power, and controlling the step motors for the X,Y coordinates. The equipment and procedure enable laser scanning of sample multielement photodetectors, with external dimensions 10 × 10 μm2 to 150 × 150 mm², along the X, Y coordinates at a maximum rate of 100 mm/sec; minimum radiation power of the laser diodes, 10 mW; range of laser beam diameters, 2–50 μm; range of scanning steps along the X, Y coordinates, 5–100 μm; current sensitivity 1·10⁻⁸ A, voltage sensitivity 1·10⁻⁷ V; measurement and analysis accuracy at least 0.5%; storage of color plots of the inhomogeneities in the active regions of the multielement photodetectors on the hard disk of the personal computer, with output of analysis results to a monitor and color printer, 32 color gradations. Software written in Delphi 7.0. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 277–280, March–April, 2006.     

Mechanooptical investigations of polyimide films exposed to electrons,mechanical loads,and temperatures

Joint effect of high-energy electrons, mechanical loads, and temperature on polyimide films of thicknesses in the range 30–130 μm is investigated. The films were preliminary irradiated by electrons in air using an éLU-6 linear accelerator with energy of 2 MeV and doses D = 1, 5, 10, 20, 30, 40, and 100 MGy and then subjected to uniaxial mechanical tension at temperatures (T) from 293 to 593 K. It is established that at T = 293–450 K and D = 20–40 MGy, the mechanical load causes almost the same deformations (ε_{l max}) of nonirradiated and irradiated samples; at T = 450–550 K, deformations of films sharply increase, and the character of their dependence changes. The ε_{l max} value of the initial sample increases almost linearly with temperature by a factor of 10, whereas the character of changing ε_{l max}(T) of the irradiated films is more complex, and its value increases approximately by a factor of 4. For T > 500 K, the deformation reaches limiting values. Irradiation increases the intensity of IR-spectra by 2–6 times and essentially increases the widths of absorption bands at 720, 1380, and 1775 cm⁻¹, which is caused by the formation of hydrogen bonds and cycles with nitrogen as well as by the formation of nitrogen oxides. External loading applied to film rupture causes an increase in the EPR signal amplitude from 3·10³ to 5·10³, which is connected with an increased concentration of radicals =N-H and-NH ₂. The electron irradiation of the polyimide films with their subsequent mechanical loading causes the spectrum lines to displace from 3475.0 to 3512.5 cm⁻¹ with simultaneous reduction of the signal amplitude from 6·10³ to 4·10³. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 52–58, February, 2007.     

Excess noise in YBa2Cu3O7 epitaxial films and antenna-type microbolometers based on them

Monte Carlo modelled anneals of YBa₂Cu₃O₇ epitaxial films have been carried out, and the excess flicker noise in the operating frequency and temperature ranges were shown to be dominated by oxygen migration near small-angle block boundaries. Optimization of film and planar-microstructure fabrication permitted reaching a record-low Hooge noise parameter (1.8×10⁻⁴ at 93 K) for test structures, which can be used to prepare high-performance antenna-type strip microbolometers. Calculations show that the reduction of the microstrip size to 1×0.7 μm² and of the flicker noise made possible detection of radiation within the spectral range from 3 mm to 300 μm (100–1000 GHz) at 90 K, with a nanosecond response and a noise-equivalent power of 1.5×10⁻¹² W/Hz^1/2 at frequencies from 30 to 10⁷ Hz, which is close to the limitations imposed by phonon noise. Fiz. Tverd. Tela (St. Petersburg) 41, 1931–1935 (November 1999)     

Dosed extraction of hydrogen from a layered thin-film system

Radiation-stimulated interfacial gas release in an Ag-glass thin-film system is investigated. It is established that under proton irradiation hydrogen accumulates in bubbles, which are the interfacial gas reservoirs, at the interface. The gas bubbles formed are studied and their parameters are determined by optical microinterferometry. It is shown that 15–50 μm in radius bubbles contain 2×10⁹–2×10¹¹ hydrogen molecules. Hydrogen is extracted from the reservoir by rupturing the thin-film dome of a bubble with a 2×10¹³ W·cm⁻² laser beam. Zh. Tekh. Fiz. 69, 112–115 (February 1999)     

Generation of coherent tunable deep UV radiation for detection and absorption studies of explosives RDX and TNT

We report a technique for the efficient generation of tunable coherent deep UV radiation and its application in studies of RDX and TNT at the ppm level on the basis of their absorption characteristics. The obtained experimental absorption data are compared with conventional spectrophotometric data. The UV radiation in the range 200–260 nm has been generated by the type-I noncollinear third harmonic of the dye laser radiation (600–700 nm) and also by sum frequency mixing (SFM) of Nd:YAG output (1064 nm) with the second harmonic of the dye laser in β-barium borate (BBO) crystal. The maximum conversion efficiency of the generated signal is estimated to be 57.5% at λ = 218.9 nm wavelength. Apart from measurements of the absorbance of RDX and TNT at different concentrations in their respective solutions, the minimum detection concentrations have also been ascertained. The estimated minimum detectable concentration of RDX is 8.47·10⁻⁹ M, whereas that for TNT is 35.7·10⁻⁹ M. The data were obtained using only ∼100 μJ/pulse of laser energy. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 516–521, July–August, 2007.     

Generation and transport of high-current, low-energy electron beams in a system with a gas-filled diode

Investigations of the generation and transport of a high-current, low-energy electron beam are performed in a system with a gas-filled diode based on a plasma cathode. At accelerating voltages of up to 20 kV and pressures of (1–5)×10⁻¹ Pa, a beam with an emission current of 600 A, emission current density of 12 A/cm² and pulse duration of 30 μs if obtained in a diode with a grid-stabilized emission opening having a diameter equal to 8 cm. The beam is transported in the absence of an external magnetic field over a distance of 20 cm. The beam is compressed by its self-magnetic field, and the current density at the collector reaches 100 A/cm² when the beam diameter is 3 cm. Zh. Tekh. Fiz. 68, 44–48 (January 1998)     

Comparison of optical properties and mechanical/electrical degradation of some low density polyethylene-and polypropylene-based polymer blends

In this study, the optical properties as well as mechanical and electrical degradation of low-density polyethylene (LDPE)/polypropylene fiber (PP fiber) (10–50% PP fiber), polypropylene (PP)/PP fiber (10–50% PP fiber), and LDPE/diamond (0.1–3% diamond) blends, which are prepared by hot pressing method, with changing thicknesses ranging from 30 to 225 μm, are compared. The spectra, in the wavelength range 200–2500 nm, are examined. Based on optical absorption spectra obtained, Tauc graphs are plotted. Determined values of the direct optical energy gap (E _d ^opt ), the indirect optical energy gap (E _i ^opt ), the width of the band (ΔE), and ultraviolet transmittance (T_UV) are listed. The direct E _d ^opt and indirect E _i ^opt values for organic blends are in the range of 3.10–3.17 eV and 1.52–2.99 eV; for inorganic blends they are 1.80–4.13 eV and 1.55–4.7 eV respectively. The electrical strength (ε) and the mechanical tension (σ) have been investigated, and graphs (the dependence of the electrical life time log τ_ε on ε) are given. The experimental results are analyzed from the viewpoint of the validity of the thermofluctuation theory. LDPE and LDPE/0.5% diamond composite parameters consecutively changed: σ from 68 to 82 MPa, ε from 60·10⁶ to 85·10⁶ V/m, mechanical lifetime τ_σ from 10 to 1.5·10⁵ sec, electrical lifetime τ_ε from 2· 10³ to 2·10⁵ sec, and structure-sensitive parameters γ and χ — from 1.48 to 1.18 (J)MPa/mole and from 0.97 to 0.70 (J)Vm⁻¹/mole respectively. The values of mechanical and electrical durability were observed to increase by 20 and 41%, respectively, for LDPE/0.5% diamond composite. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 677–683, September–October, 2007.     

Enhancement of ablation smoothing in laser-irradiated,highZ coated,thin foil targets

An enhanced spatial smoothing of ablative motion of thin plastic foil targets coated with high atomic number ablators such as gold or aluminium, irradiated by a spatially modulated Nd: glass laser beam was observed. Optical shadowgraphy coupled with double foil technique was used to observe the laser-irradiated foil motion. Laser irradiance used for the experiments was in the range of 10¹¹–10¹³ watts/cm². A 60–80% enhancement in the smoothing was observed for a laser beam modulation (width 75–150 μm) at the target surface.     

Particular features of the transmission of laser radiation with wavelength 0.438 µm and intensity (3–7)·1014 W/cm2 through an undercritical plasma from polymer aerogels

The velocities of energy transport in an undercritical plasma of polymer aerogel with and without copper nanoparticles were measured. Transmission of the laser light through targets of different thicknesses such as submicron three-dimensional polymer networks with densities below the critical value (0.13–0.52 N _cr) for a wavelength of 0.438 μm and intensity of (3–7)·10¹⁴ W/cm² at a half-height pulse duration of 0.32 ns was studied. The transfer of a heating laser radiation was registered on the rear side of the target. It ranged from a level of ∼0.5% for the thickness of a low-density layer of 400 μm and density of 9 mg/cm³ (mass per unit square of 0.36 mg/cm²) up to 50–60% for a thickness of 100 μm and density of 2.25 mg/cm³ (mass per unit square of 0.02 mg/cm²). The time dependences of the optical emission from the rear side of the targets were measured. They appear to be indicative of the plasma dynamics in two-layer targets (polymer foam on Al foil) and enable the estimation of the absorption depth for the laser light in an undercritical plasma. __________ Translated from Preprint No. 8 of the P. N. Lebedev Physical Institute, Moscow (2007).     

Fabrication of anode supported thick film ceria electrolytes for IT-SOFCs

Anode supported thick film ceria electrolyte unit cells were fabricated using a colloidal dip coating method for IT-SOFCs. Pre-sintering temperature of the anode substrate and the final sintering temperature were found to be the primary parameters determining the density of the film. With Ni-Ce_0.89Gd_0.11 O_2–δ cermet anode, La_0.6Sr_0.4Co_0.2Fe_0.8O₃ cathode and 15 μm Ce_0.89Gd_0.11 O_2–δ electrolyte, the cells were tested in a fuel cell configuration with air at the cathode and moist H₂ at the anode. At 650 °C, the cell indicated a maximum power density of ∼0.27 W/cm² at a current density of 0.62 A/cm². Cell performance was compared with oxygen at the cathode and the cell indicated a maximum power density of ∼0.50 W/cm² at 1.14 A/cm², 650 °C. Activation energy for the area specific resistance (ASR) of the cell suggests that with air at cathode, the cell performance was limited by gaseous diffusion at cathode and with oxygen at cathode, by oxygen ion transport across the electrolyte.     

X-ray and luminescent analysis of finely dispersed β-FeSi2 films formed in Si by pulsed ion-beam treatment

Finely dispersed β-FeSi₂ films were formed by implanting Fe⁺ ions with an energy of 40 keV and a dose of 1×10¹⁶ cm⁻² in Si single crystals, followed by nanosecond pulsed ion-beam treatment. The results of glancing incidence x-ray diffraction indicate the formation of a highly grain-oriented film consisting of inclusions of the iron disilicide phase (β-FeSi₂) with a grain size of approximately 40 nm surrounded by a polycrystalline Si matrix. The photoluminescence spectroscopy data reveal that the photoluminescence signal with a peak around 1.56 μm, which is observed up to 210 K, is associated with direct interband transitions in β-FeSi₂ and not with the contribution from the dislocation-induced line D1. __________ Translated from Fizika Tverdogo Tela, Vol. 43, No. 9, 2001, pp. 1569–1572. Original Russian Text Copyright ? 2001 by Bayazitov, Batalov, Terukov, Kudoyarova.     

Evaporation of millimeter water drops in the field of IR laser radiation

The evaporation of large (∼10⁻³ m across) water drops in the field of IR (10.6 μm) laser radiation of power density (4–12)×10⁵ W/m² is considered. Qualitative analysis shows that the process is described well with an optical cavity model. A mechanism of water evaporation is found to be associated with surface electromagnetic waves, which break hydrogen bonds in the high-frequency (≈3×10¹³ s⁻¹) field of the laser. The theory is in good agreement with experimental data. Original Russian Text ? V.I. Trigub, 2006, published in Zhurnal Tekhnicheskoĭ Fiziki, 2006, Vol. 76, No. 4, pp. 120–123.     

Simple and sensitive spectrophotometric methods for determination of amantadine hydrochloride

Three simple and sensitive spectrophotometric methods (A–C) for determination of amantadine hydro-chloride have been developed and validated. The first method (A) is based on the oxidation of the drug by ammonium molybdate. The second method (B) was based on the charge-transfer complexation reaction between the amantadine base as an electron donor and iodine as a σ-acceptor. The third method (C) is based on the reaction of N-alkylvinylamine formed from the interaction of the free amino group in amantadine molecule and acetalde-hyde with chloranil to give colored vinylamino-substituted benzoquinone. The colored products of these reactions were measured at their corresponding maximum absorption peaks. Different variables affecting the reactions were carefully studied and optimized. Under the optimum conditions, linear relationships with good correlation coefficients 0.9993–0.9998 were found between the reading and the corresponding concentration of the drug in the range 2–90 μg·ml⁻¹. The limits of detection ranged from 0.16 to 1.91 μg·ml⁻¹. The precision of the methods was satisfactory: the values of relative standard deviation did not exceed 1.63%. The proposed methods were successfully applied to the analysis of amantadine HCl in its capsules with good accuracy and precision; the label claim percentages ranged from 99.8 to 100.5 ± (0.52–1.22) %. The results obtained by the proposed spectrophotometric methods were comparable with those obtained by the official method. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 707–712.     

Neutron events in the underground monitor of the Tien Shan high-altitude station

The neutron multiplicity M spectrum was measured at the neutron monitor installed in the underground room of the Tien Shan high-altitude station (3340 m above sea level) of the Lebedev Physical Institute under a ground layer 20 m of water equivalent thick. To a first approximation, the differential multiplicity spectrum is power-law: dN/dM = 0.3 · M^−3.7m⁻²s⁻¹. The spectrum intensity is lower than the intensity of events in the ground-based NM64 supermonitor by a factor of 350–450. The spectrum slope exponent γ + 1 = 3.7 ± 0.1 is identical to the exponent of the energy spectrum of bremsstrahlung gamma-rays of energetic muons (above 1 TeV) generated in a lead absorber of the monitor. In this case, the experimental intensity is hundred times higher than the expected intensity of events from muon bremsstrahlung. The spatial distribution of neutrons in the monitor suggests that they are produced by single particles. The temporal distribution of neutrons in the monitor is exponential with lifetime constant τ = 360 − 390 μs. Difficulties are indicated in the interpretation of the multiplicity spectrum by electromagnetic and nuclear interactions of muons in the monitor without involving new penetrating particles. Original Russian Text ? A.P. Chubenko, A.L. Shchepetov, L.I. Vildanova, M.I. Vildanova, P.A. Chubenko, 2007, published in Kratkie Soobshcheniya po Fizike, 2007, Vol. 34, No. 4, pp. 21–31.     

The dynamics of accumulation of electrically active radiation defects on implantation of graded-band-gap HgCdTe films grown by MBE

The dynamics of accumulation of electrically active radiation defects under ion doping of epitaxial Cd _x Hg _1−x Te films is studied for various distributions of film composition in the implantation region. The epitaxial films were irradiated by boron ions at room temperature in the continuous regime, with the dose ranging within 10¹¹−3·10¹⁵ cm⁻², energy — 20–150 keV, and ion current density — j = 0.001–0.2 μA·cm⁻². It is found that the natural logarithm of the introduction rate of electrically active radiation defects linearly depends on the epitaxial-film composition in the range of mean projected path of implanted ions. An analysis of the experimental data shows that the dynamics of accumulation of electrically active radiation defects is determined by the epitaxial-film composition in the implantation region. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 25–28, September, 2006.