The article is devoted to the study and thermodynamic justification of the method for obtaining dilute solutions of rare earth metal trichlorides by chlorination of their oxides in a molten equimolar mixture of NaCl – KCl. And the effectiveness of this method is demonstrated by the example of lanthanum (III) and neodymium (III) oxides. Gibbs free energy of the reactions of La2O3 and Nd2O3 chlorination by different chlorinating agents has been calculated. The interaction of lanthanum (III) and neodymium (III) oxides in the molten equimolar mixture NaCl – KCl depending on the chlorination time and the material of reaction vessel (beryllium oxide and glass-carbon) has been studied experimentally. The results of thermodynamic modelling of the chlorination reactions of La2O3 and Nd2O3 by gaseous chlorine in this salt melt are presented. In the case of using a molten equimolar mixture of NaCl – KCl, a significant shift of the Gibbs energy to the negative region is observed compared with chlorination without the use of a salt medium. The effectiveness of chlorine as a chlorinating agent in the melt is based on the fact that in liquid NaCl-KCl Ln3+ ions form complexes with very small activity coefficient. The removal of synthesized lanthanum trichloride from the chlorination reaction zone due to its solubility in a low-viscosity NaCl-KCl melt has a beneficial effect on the rate of its flow. It has been shown that the formation of rare earth metal trichlorides occurs through the formation of LaOCl and NdOCl oxychlorides. The advantages of the proposed method of chlorination of rare earth metal oxides (REM) in the synthesis of solutions of their trichlorides in molten salts are shown.

Studies of the laser-induced ultrafast processes in thin films are of significant importance for the development of microelectronics. These processes include the heating of an electron subsystem, relaxation and transport of the absorbed energy, and generation and propagation of picosecond acoustic waves. In view of this circumstance, to study the dynamics of variation of the differential reflection coefficient ΔR(t)/R0 of a 73-nm-thick Ni film on a glass substrate, pump–probe measurements have been performed in this work with the synchronous detection of a ΔR(t)/R0 signal. High absorbed fluences up to 11 mJ/cm2 have been reached by increasing the pulse-repetition interval tcool of heating (pump) pulses. An increase in tcool makes it possible to better cool the film after heating. As a result, record temperatures Te ≈ 3 kK and Ti ≈ 1 kK and stresses up to 7 GPa have been reached for the first time to the best of our knowledge. These high values have allowed the observation of nonlinear effects for the first time in experiments with synchronous detection.

Ultrashort laser pulses with a duration from several to about a thousand optical cycles have significant importance in modern science and engineering. Such a pulse transfers a metal to an excited two-temperature state with hot electrons where the temperature of the electron subsystem T e is much higher than the temperature of the ion subsystem T i . The thermal conductivity in such systems differs from well-known reference values. The thermal conductivity κ and the energy exchange rate between the electron and ion subsystems α are the key parameters of the two-temperature model, which are still poorly studied, although studies of these parameters, particularly α, are numerous. New theoretical and experimental results that make it possible to determine the parameters κ and α for gold have been reported in this work.

Ультракороткие лазерные воздействия с длительностью от нескольких до порядка 1000 световых осцилляций имеют огромное значение в современных науке и технике. Такой импульс переводит металл в возбужденное состояние с горячими электронами: двухтемпературное состояние Te ≫ Ti, где Te, Ti - это температуры электронной и ионной подсистем. При этом меняется коэффициент теплопроводностипо сравнению с хорошо известными справочными значениями. Теплопроводность κ и темп обмена энергией между электронной и ионной подсистемами α - это ключевые параметры 2T модели. До сих пор они остаются плохо изученными. Хотя работ, направленных на их исследование, особенно это касается α, много. В настоящей статье представлены новые теоретико-экспериментальные данные, позволяющие определить κ и α на примере с золотом.

The deposition of LiCoO 2 nanosized particles synthesized in LiCl–CoCl 2 melts on the surface of nickel foil, copper, chrome–cobalt alloy, and platinum mesh in aqueous solutions of lithium chloride at the room temperature as well as on the surface of the electron-conducting La 0.6 Sr 0.4 MnO 3 oxide ceramics in chloride melt at temperature of ca. 700°C is studied. The methods of vibrational spectroscopy, X-ray photoelectron spectroscopy, ellipsometry, and scanning electron microscopy have revealed the features of the chemical composition, structure, and morphology of the precipitates obtained.

The temporal dynamics of the change in the thermally-induced induced reflection coefficient of polycrystalline gold, aluminum, and molybdenum at a wavelength of 800 nm as a result of exposure to a femtosecond laser pulse (at a wavelength of 400 nm) with an intensity of up to 0.2 TW in the in the picosecond time range is studied using pump-probe optical scheme with phase-sensitive detection. New experimental data are obtained on the change in the reflection coefficient under strongly nonequilibrium conditions when the electron subsystem is heated to temperatures of 10 kK, which are relevant for the development of the experimental base for numerical simulation.

The results of experimental studies of the laser shock waves initiated by a picosecond pulse in iron are presented. Experimental measurements are processed and analyzed using theoretical approaches and numerical simulation. Interest in picosecond actions is caused by uniquely high strain rates, in particular, the dependence of the thresholds of elastoplastic and polymorphic transformations on the strain rate. Investigations are necessary for the development of the field of laser hardening of metals. The first steps in this direction have been taken, although this kind of approach to laser forging hardening is already widely used in practice. Modern developments in the field of shock wave generation and their experimental diagnostics are used, and the related methods of theoretical interpretation of experimental data are being developed. The difficulty lies in the picosecond time scale, since the diagnostics of experiments is limited by kinematics, namely, measuring the coordinates of the free surface. To elucidate the polymorphic transformation kinetics on picosecond time scales, the technique of inverse analysis of the free surface velocity is used for the first time. This technique is validated using the results of hydrodynamic and molecular dynamics simulation with direct extraction of mechanical stresses and strains. A theoretical study of reconstructed free surface velocity profiles by traditional methods confirms the results obtained in the field of their applicability, specifically, on elastic and plastic shock wave fronts. The transformation of iron into the ε phase takes place in the initial region of shock wave propagation, as long as a shock wave has a sufficient amplitude. The cause is a pressure limitation of 40 GPa because of optical breakdown in glass and shock wave attenuation during wave propagation.

Laser shock peening with ultrashort laser pulses has been studied by hydrodynamic and atomistic simulations, as well as experimentally. It has been shown that, in contrast to traditional nanosecond pulses, ultrashort laser pulses allow one to increase the produced pressures by two or three orders of magnitude from 1–10 GPa to 1000 GPa (1 TPa). The physics of phenomena changes fundamentally because shock waves generating pressures exceeding the bulk modulus of a metal melt it. It has been shown for the first time that the shock melting depth at pressures about 1 TPa is an order of magnitude larger than the thickness of the melt layer caused by heat conduction. The appearance, propagation, and damping of a melting shock wave in titanium have been studied. The damping of the shock wave makes it possible to modify the surface layer, where the melting regime changes from a fast one in the shock jump to a slow propagation of the melting front in the unloading tail behind the shock wave. It has been shown experimentally that the ultrafast crystallization of the melt forms a solid layer with a structure strongly different from that before the action. The measured depth of this layer is in good agreement with the calculation.

Ablation in liquid is numerically simulated with molecular dynamics and hydrodynamics codes. Laser radiation passes through a transparent liquid, illuminates a metal target, and is absorbed in it and reflected from it. The range of absorbed fluences F abs about 1 J/cm 2 is considered, which is of technological interest: the number of nanoparticles formed per laser pulse below these values is small, whereas the optical breakdown of the liquid occurs above them. A theory is developed to estimate the mass and composition of nanoparticles formed by laser radiation using simulation data and thermodynamic information (equation of state of matter).

Elastic-plastic transformations together with or separately of polymorphic phase transitions are important for the theory of shock waves. Here we discuss changing a classification consisting from elastic, split elastic-plastic, and pure plastic shocks. The split shocks means that there are two jumps: the elastic precursor and plastic shock, and that the elastic jump is independent relative to plastic one. In the split regime the precursor moves with elastic speed of sound overrunning the plastic jump and going further and further ahead relative to plastic jump as time proceeds and becoming weaker and weaker. We oppose the split shock to the one-wave (1W) two zones (elastic and plastic—2Z) shock (1W2Z shock). The 1W2Z wave propagates as whole (therefore one-wave), the plastic shock dynamically supports the elastic one, and the average distance between the jumps does not change in time. The powerful elastic shocks (their amplitudes are much higher than are usually suggested for elastic shocks) were found in experiments with femtosecond laser pulses and confirmed in large scale molecular dynamics (MD) simulations. The observation of the 1W2Z shocks is another important finding coming from MD. The report is devoted to lasers, shocks, and applications. In the second part of the report the generation and propagation of the shocks created for laser shock peening by lasers with ultrashort or nanosecond pulses are considered.

Abstract Analytical expressions for the electron thermal conductivity of nickel and aluminum are presented. The thermal conductivity depends on the electronic and ionic temperatures, density and phase of the substance (solid or liquid). The expressions obtained can be used in hydrodynamic calculations of the ablation of these metals or multilayer targets made from them. We consider the case when ablation is caused by the action of ultrashort laser pulses.

Воздействие двух последовательных лазерных импульсов на кремний, помещенный в глицерин, исследовано экспериментально и численно с помощью программ электромагнитного, гидродинамического и атомистического моделирования. Показано, что после первого импульса на поверхности образуется микропузырек в жидкости, на котором затем происходит дифракция второго импульса, ширина светового пучка которого сравнима с диаметром микропузырька. Мы рассчитали дифракционную картину и распределение интенсивности света на поверхности кремния, и оказалось, что максимальная интенсивность в дифракционных пиках может заметно превышать интенсивность на оси падающего гауссова пучка. В результате усиления интенсивности, сконцентрированной в одном ярком узком кольце вокруг микропузырька, на кремнии образуется характерная канавка, окруженная валиками. Мы продемонстрировали в молекулярно-динамическом расчете, что интенсивный нагрев в дифракционном пике вызывает плавление и вытеснение расплава от центра прогрева. Это приводит к формированию канавок с валиками, имеющими профиль, подобный измеренному в эксперименте.

The effect of two successive laser pulses on silicon placed in glycerol has been studied experimentally and numerically with electromagnetic, hydrodynamic, and atomistic simulation programs. It has been shown that a microbubble in the liquid is formed on the surface after the first pulse; then, the second pulse whose width is comparable with the diameter of the microbubble is diffracted on this microbubble. The calculated diffraction pattern and light intensity distribution on the silicon surface indicate that the maximum intensity at the diffraction peaks can be noticeably higher than the intensity on the axis of the incident Gaussian beam. An increase in the intensity concentrated in one bright narrow ring around the microbubble results in the formation of a characteristic groove surrounded by ridges on silicon. The molecular dynamics simulation has shown that intense heating at the diffraction peak is responsible for the melting and displacement of the melt from the center of heating. This leads to the formation of grooves with ridges having a profile similar to that measured in the experiment.

Multilayer products made of ultra-thin layers are widely used in modern science and technology. Laser exposure is used as one of the promising methods of processing such products. In this regard, we study the ablation of a layered target. A physical model is constructed, numerical simulation is performed, and experiments are carried out. The experiments were conducted with two different lasers and various diameters of the focal spot. To estimate the absorbed energy the reflection coefficient was measured. The results of calculations and experiments are consistent with an accuracy of about 10%. This allowed us to refine the model of two-temperature states and determine the strength of nickel. It is explained why, with an increase in the absorbed fluence, first the upper layer breaks in the multilayer.

The selective modification of upper layers of a Ni/Al multilayer nanostructure irradiated by a single femtosecond laser pulse has been studied. The analysis of surface topography indicates that either partial or complete removal of two upper layers is possible depending on the absorbed energy. The surface has been scanned by an atomic force microscope. The numerical simulation of the phenomenon with a two-temperature hydrodynamic code has revealed an asynchronous dynamics of the electron subsystems of Ni and Al and an inhomogeneous heating of ion subsystems. As a result, a complex combination of compression and rarefaction waves is initiated in the multilayer target. It has been shown numerically that, as the absorbed energy increases, the first nickel layer is initially ruptured because of the localization of tensile stresses. The experimental and numerical thicknesses of the separated layer and the threshold energy are in agreement with each other. Consequently, the parameters of two-temperature models of nickel and aluminum are selected correctly.