Landau damping in thin films irradiated by a strong laser field

The rate of linear collisionless damping (Landau damping) in a classical electron gas confined to a heated ionized thin film is calculated. The general expression for the imaginary part of the dielectric tensor in terms of the parameters of the single-particle self-consistent electron potential is obtained. For the case of a deep rectangular well, it is explicitly calculated as a function of the electron temperature in the two limiting cases of specular and diffuse reflection of the electrons from the boundary of the self-consistent potential. For realistic experimental parameters, the contribution of Landau damping to the heating of the electron subsystem is estimated. It is shown that for films with a thickness below about 100 nm and for moderate laser intensities it may be comparable with or even dominate over electron-ion collisions and inner ionization.Comment: 15 pages, 2 figure

Melting Point and Lattice Parameter Shifts in Supported Metal Nanoclusters

The dependencies of the melting point and the lattice parameter of supported metal nanoclusters as functions of clusters height are theoretically investigated in the framework of the uniform approach. The vacancy mechanism describing the melting point and the lattice parameter shifts in nanoclusters with decrease of their size is proposed. It is shown that under the high vacuum conditions (p<10^-7 torr) the essential role in clusters melting point and lattice parameter shifts is played by the van der Waals forces of cluster-substrate interation. The proposed model satisfactorily accounts for the experimental data.Comment: 6 pages, 3 figures, 1 tabl

Сравнительное исследование электроискровых покрытий, полученных с использованием электродов TiC–NiCr и TiC–NiCr–Eu2O3

The study covers coatings obtained on 40Kh steel substrates by electro-spark deposition (ESD) using TiC–NiCr and TiC–NiCr– Eu2O3 electrodes. Coatings were deposited by the Alier-Metal 303 unit in argon environment under the normal pressure using direct and opposite polarity. The structure, elemental and phase composition of electrodes and coatings were studied using X-ray phase analysis, scanning electron microscopy, energy dispersive spectroscopy, glow discharge optical emission spectroscopy, and optical profilometry. Mechanical and tribological properties of coatings were determined by nanoindentation and testing according to the «pin-disk» scheme including high-temperature conditions in the range of 20–500 °C. The tests conducted include abrasive wear tests using the Calowear tester, impact resistance tests using the CemeCon impact tester, and tests for gas and electrochemical corrosion resistance. Test results showed that electrodes contain titanium carbide, nickel-chromium solid solution, and europium oxide in case of a doped sample. Coatings exhibit the same phase composition but solid solution is formed on the iron base. Coatings with the Eu2O3 additive do not differ significantly in structural characteristics, hardness, friction coefficient, and exceed the base coatings in terms of their abrasive resistance, repeated impact resistance, heat and corrosion resistance. There was an increase in impact resistance by 1.2–2.0 times, a decrease in corrosion current by more than 20 times, and an oxidation index by almost 2 times during the transition to doped coatings.Исследованы покрытия, полученные на подложках из стали 40Х методом электроискрового легирования с использованием электродов TiC–NiCr и TiC–NiCr–Eu2O3. Покрытия наносились с помощью установки «Alier-Metal 303» в среде аргона при нормальном давлении в режиме прямой и обратной полярности. Структура, элементный и фазовый составы электродов и покрытий были изучены посредством рентгенофазового анализа, растровой электронной микроскопии, энергодисперсионной спектроскопии, оптической эмиссионной спектроскопии тлеющего разряда и оптической профилометрии. Механические и трибологические свойства покрытий определялись методом наноиндентирования и путем испытаний по схеме «стержень–диск», в том числе при повышенных температурах в диапазоне 20–500 °С. Проведены исследования на абразивный износ с использованием прибора «Calowear-tester», стойкость к динамическим воздействиям с помощью установки «CemeCon impact-tester» и стойкость к газовой и электрохимической коррозии. Полученные результаты показали, что электроды содержат карбид титана, твердый раствор никеля в хроме и оксид европия в случае допированного образца. Покрытия также включали данные фазы, однако твердый раствор формировался на основе железа. Покрытия с добавкой Eu2O3 по структурным характеристикам, твердости, коэффициенту трения существен- но не отличались, а по стойкости к абразивному износу и к циклическим ударным нагрузкам, жаро- и коррозионной стойкости превосходили базовые покрытия. Наблюдались увеличение стойкости к ударным нагрузкам в 1,2–2,0 раза, понижение тока коррозии более чем в 20 раз и уменьшение показателя окисления почти в 2 раза при переходе к допированным покрытиям

Guided electromagnetic discharge pulses driven by short intense laser pulses:Characterization and modeling

Strong electromagnetic pulses (EMPs) are generated from intense laser interactions with solid-density targets and can be guided by the target geometry, specifically through conductive connections to the ground. We present an experimental characterization by time- and spatial-resolved proton deflectometry of guided electromagnetic discharge pulses along wires including a coil, driven by 0.5 ps, 50 J, 1019 W/cm2 laser pulses. Proton-deflectometry allows us to time-resolve first the EMP due to the laser-driven target charging and then the return EMP from the ground through the conductive target stalk. Both EMPs have a typical duration of tens of ps and correspond to currents in the kA-range with electric-field amplitudes of multiple GV/m. The sub-mm coil in the target rod creates lensing effects on probing protons due to both magnetic- and electric-field contributions. This way, protons of the 10 MeV-energy range are focused over cm-scale distances. Experimental results are supported by analytical modeling and high-resolution numerical particle-in-cell simulations, unraveling the likely presence of a surface plasma, in which parameters define the discharge pulse dispersion in the non-linear propagation regime.</p

Guided Electromagnetic Discharge Pulses Driven by Short Intense Laser Pulses: Characterisation and Modelling

Strong electromagnetic pulses (EMP) are generated from intense laser interactions with solid-density targets, and can be guided by the target geometry, specifically through conductive connections to the ground. We present an experimental characterization, by time- and spatial-resolved proton deflectometry, of guided electromagnetic discharge pulses along wires including a coil, driven by 0.5 ps, 50 J, 1e19 W/cm2 laser pulses. Proton-deflectometry data allows to time-resolve first the EMP due to the laser-driven target charging and then the return EMP from the ground through the conductive target stalk. Both EMPs have a typical duration of tens of ps and correspond to currents in the kA-range with electric-field amplitudes of multiple GV/m. The sub-mm coil in the target rod creates lensing effects on probing protons, due to both magnetic- and electric-field contributions. This way, protons of 10 MeV-energy range are focused over cm-scale distances. Experimental results are supported by analytical modelling and high-resolution numerical particle-in-cell simulations, unraveling the likely presence of a surface plasma, which parameters define the discharge pulse dispersion in the non-linear propagation regime

Возможности многоугловой спектрофотометрии для определения параметров пленок на однослойных структурах

Single-layer Ta-Si-C-N films on fused quartz substrates were made by direct current magnetron sputtering. The structural perfection of the film was investigated by X-ray diffraction analysis, scanning electron microscopy and optical emission spectroscopy of glow discharge. The optical parameters of the films were determined by the method of multi-angle spectrophotometry. Spectral dependences of the transmission coefficients of substrates and structures at normal light incidence in the wavelength range of 200—2500 nm are obtained. It is shown that the transmission spectrum of the sample has an oscillating character, which is caused by interference phenomena characteristic of layered structures. Spectral dependences of the reflection coefficients of films and substrates in the wavelength range of 200—2500 nm at small angles of incidence of light are obtained. By the magnitude of the difference between the reflection coefficient at the maximum of the interference of the film and the corresponding reflection coefficient of the substrate at the same wavelength, it is shown that the absorption in the film is low. A formula is obtained for determining the absorption coefficient of a film from the measured parameters. Based on the experimental data obtained, spectral dependences of the absorption coefficients of the substrate, structure and film are constructed. The method of reflection at two angles of incidence, based on the determination of the position of the interference extremes on the spectral dependences of the reflection coefficients, calculated discrete values of the refractive coefficients in the wavelength range 400—1200 nm. The obtained values are approximated by the Cauchy equation. The film thickness was calculated, which was d = 1046 nm ± 13%. Spectral dependences of the film attenuation indices with and without reflection are constructed. A summary table is presented with the obtained values of the refractive coefficients and absorption indices with and without reflection.Методом магнетронного распыления постоянного тока изготовлены однослойные пленки Ta—Si—C—N на подложках из плавленого кварца. Структурное совершенство пленок исследовано методами рентгеноструктурного анализа, сканирующей электронной микроскопии и оптической эмиссионной спектроскопии тлеющего разряда. Оптические параметры пленок определены методом многоугловой спектрофотомерии. Получены спектральные зависимости коэффициентов пропускания подложек и структур при нормальном падении света в диапазоне длин волн 200—2500 нм. Показано, что спектр коэффициентов пропускания образца имеет осциллирующий характер, который обусловлен интерференционными явлениями, характерными для слоистых структур. Измерены спектральные зависимости коэффициентов отражения пленок и подложек в диапазоне длин волн 200—2500 нм при малых углах падения света. По величине разницы между коэффициентом отражения в максимуме интерференции пленки и соответствующим коэффициентом отражения подложки при этой же длине волны показано, что поглощение в пленке мало. Получена формула для определения коэффициента поглощения пленки по измеренным параметрам. На основании экспериментальных и расчетных данных построены спектральные зависимости коэффициентов поглощения подложки, структуры и пленки. Методом отражения при двух углах падения, основанном на определении положения интерференционных экстремумов на спектральных зависимостях коэффициентов отражения, рассчитаны дискретные значения коэффициентов преломления в диапазоне длин волн 400—1200 нм. Полученные величины аппроксимированы уравнением Коши. Рассчитана толщина пленки, которая составила dпл. = 1046 нм ± 13 %. Построены спектральные зависимости показателей ослабления пленки с учетом и без учета отражения. Представлена сводная таблица с полученными значениями коэффициентов преломления и показателей поглощения с учетом и без учета отражения

Guided electromagnetic discharge pulses driven by short intense laser pulses : Characterization and modeling

Strong electromagnetic pulses (EMPs) are generated from intense laser interactions with solid-density targets and can be guided by the target geometry, specifically through conductive connections to the ground. We present an experimental characterization by time- and spatial-resolved proton deflectometry of guided electromagnetic discharge pulses along wires including a coil, driven by 0.5 ps, 50 J, 1019 W/cm2 laser pulses. Proton-deflectometry allows us to time-resolve first the EMP due to the laser-driven target charging and then the return EMP from the ground through the conductive target stalk. Both EMPs have a typical duration of tens of ps and correspond to currents in the kA-range with electric-field amplitudes of multiple GV/m. The sub-mm coil in the target rod creates lensing effects on probing protons due to both magnetic- and electric-field contributions. This way, protons of the 10 MeV-energy range are focused over cm-scale distances. Experimental results are supported by analytical modeling and high-resolution numerical particle-in-cell simulations, unraveling the likely presence of a surface plasma, in which parameters define the discharge pulse dispersion in the non-linear propagation regime