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Non-Gaussian laser beams can open new opportunities for microfabrication, including ultrashort laser direct writing. Using a model based on Maxwell’s equations, we have investigated the dynamics of doughnut-shaped laser beams focused inside fused silica glass, in comparison with Gaussian pulses of the same energy. The laser propagation dynamics reveals intriguing features of beam splitting and sudden collapse toward the beam axis, overcoming the intensity clamping effect. The resulting structure of light absorption represents a very hot, hollow nanocylinder, which can lead to an implosion process that brings matter to extreme thermodynamic states. Monitoring the simulations of the laser beam scattering has shown a considerable difference in both the blueshift and the angular distribution of scattered light for different laser energies, suggesting that investigations of the spectra of scattered radiation can be used as a diagnostic of laser-produced electron plasmas in transparent materials.

The results of a computer simulation of time dependent, 5 2 D-MHD flows near the X-type zero line of the magnetic field are presented. The perturbations imposed from the boundary excite in the plasma an electric current directed arbitrarily with respect to the X-line: the current has components both along and perpendicular to the X-line. When the quasistationary stage is reached a system of current sheets is formed. The electric current density distribution and the local current direction are determined by the location of the magnetic field separatrix surfaces whose positions change in turn self-consistently in the course of the current sheet formation.

We present schemes for geometric phase compensation in adiabatic passage which can be used for the implementation of quantum logic gates with atomic ensembles consisting of an arbitrary number of strongly interacting atoms. Protocols using double sequences of stimulated Raman adiabatic passage (STIRAP) or adiabatic rapid passage (ARP) pulses are analyzed. Switching the sign of the detuning between two STIRAP sequences, or inverting the phase between two ARP pulses, provides state transfer with well defined amplitude and phase independent of atom number in the Rydberg blockade regime. Using these pulse sequences we present protocols for universal single-qubit and two-qubit operations in atomic ensembles containing an unknown number of atoms., Comment: 4 figures, supplemental information now included

Raman-based geobarometry has recently become increasingly popular because it is an elegant way to obtain information on peak metamorphic conditions or the entire pressure-temperature-time (P-T-t) path of metamorphic rocks, especially those formed under ultrahigh-pressure (UHP) conditions. However, several problems need to be solved to get reliable estimates of metamorphic conditions. In this paper we present some examples of difficulties which can arise during the Raman spectroscopy study of solid inclusions from ultrahigh-pressure metamorphic rocks.

In this article we demonstrate that turbulent stress contributions which depend on the rotation of the frame of reference (and therefore are system dependent) give rise to the inverse energy cascade, and thus introduce an ordering in the structure of turbulence.

Based on experiments and a theoretical analysis, we raise questions on two fundamental mechanisms of femtosecond laser desorption/ablation of solids, namely Coulomb explosion (CE) and plasma etching. The effects of laser-induced ionization and surface charging are analyzed which can be responsible for ultrafast ions observed in time-of-flight mass-spectra under ultrashort laser irradiation of solids. The importance of surface charging in formation of velocity distributions of desorbed/ablated species has been revealed for conditions when the CE mechanism is inhibited. The influence of ambient plasma formation on the dynamics of heating of metallic targets by femtosecond laser pulses is studied based on 2D modeling of laser-induced target heating and dynamics of the ambient plasma. The calculations show an intriguing picture of the laser-induced ambient gas motion. We propose a model of laser-induced breakdown of an ambient gas in a region in front of the irradiated target and analyze plasma-chemical processes which can affect laser processing of surfaces in the presence of air or highly reactive media.

Linear equations of turbulent convection in the presence of rotation are derived within the framework of a phenomenological approach. It is shown that the amplification of large-scale disturbances is possible only for the essentially inhomogeneous problem when the dimensions of the large-scale disturbance exceed the characteristic scale of density variation.

A comprehensive analysis of laser-induced modification of bulk glass by single ultrashort laser pulses is presented which is based on combination of optical Maxwell-based modeling with thermoelastoplastic simulations of post-irradiation behavior of matter. A controversial question on free electron density generated inside bulk glass by ultrashort laser pulses in modification regimes is addressed on energy balance grounds. Spatiotemporal dynamics of laser beam propagation in fused silica have been elucidated for the regimes used for direct laser writing in bulk glass. 3D thermoelastoplastic modeling of material relocation dynamics under laser-induced stresses has been performed up to the microsecond timescale when all motions in the material decay. The final modification structure is found to be imprinted into material matrix already at sub-nanosecond timescale. Modeling results agree well with available experimental data on laser light transmission through the sample and the final modification structure.

The essence of almost all processes with participation of particulate solids is similar: it is a transformation of a particle property, or properties. This suggests that a unified basis for examining the changes of this property with (for example) time, may be derived. In this paper, the general strategy of building the Markov chain models and computational analysis of characteristics of a process is described, and some examples of application of the approach to model grinding, classification, grinding with internal classification, mixing, agglomeration, etc, are shown. The use of multidimensional models to consider simultaneously different properties is emphasised. The approach also allows taking into account non-linear phenomena, which are very typical of particulate processes but are very seldom considered in usual models.

The work is aimed at investigation of dynamic and structural characteristics of the self-sustained evaporation front in freon R21 under the conditions of free convection. The results demonstrate the presence of two typical zones in the diagram of dependence of front propagation velocity on heating surface overheating. Formation of small-scaled fast growing disturbances was detected at the interface. The diagram of stability of evaporation front interface, built by the Landau theory, was proposed. The obtained experimental data were analyzed from the standpoint of instability development at intense evaporation. It is shown that development of interface instability for perturbation scales of about layer thickness corresponds to the area of more intense evaporation.

Numerical simulations based on Maxwell’s equations have been performed for gaining deep insight into the processes governing laser light absorption in transparent dielectrics in the regimes typical for laser direct writing of various optical structures inside bulk glasses such as waveguides, nanoplanes, and voids. Numerical simulations have been performed for fused silica glass irradiated by femtosecond laser pulses at 800 nm wavelength. The geometry of laser energy absorption is compared for two pulse durations and energies from 0.1 to 1 μJ. The effect of the numerical aperture of the laser energy deposition is studied. Double-pulse irradiation has been modeled to gain insight into “exciton-seeded multiphoton ionization” [Phys. Rev. B81, 212301 (2010).PRBMDO1098-0121]. Furthermore, several consecutive laser pulses have been modeled to gain a better understanding of the qualitative tendency of memory effects related to defect accumulation. Features of laser energy coupling into bulk glass such as asymmetry of absorption for the cylindrically symmetric linearly polarized beam and formation of a defect shield developing in multipulse irradiation regimes have been revealed.

The problem of the tearing instability is solved numerically in cylindrical geometry by using the unreduced two-fluid MHD model. It is shown that the duration of the nonlinear stage of the tearing instability in a hot plasma is rather sensitive to such factors as the initial radial density and temperature profiles, the initial ion-to-electron pressure ratio, and the longitudinal thermal conductivity. Depending on these factors, the two-fluid effects (primarily, the Hall effect) can either greatly hasten the magnetic reconnection process (in comparison to that in the one-fluid MHD model) or greatly slow it. An illustrative explanation of the results obtained is given.

To calculate and evaluate the efficiency of the processes of fractionation of particulate solids, various industry methods have been developed that are widely and successfully used for the analysis of specific industrial technologies. Different indicators are used to measure the strength properties of particles of a bulk material in various industrial technologies. The disadvantage of the situation is the complexity, and often the impossibility of using these specific indices of strength of materials for calculating the grinding process in new equipment or a new range of particle sizes. Significant energy consumption for grinding at low efficiency of industrial mills causes the necessity of carrying out the studies aimed to increasing the efficiency of fractionation of particulate solids. In connection with this, the actual problem of scientific research to develop a generalized and universal energy indicator of grindability particulate solids and a method for its determination that can be used to describe the grinding process and to evaluate its efficiency in various industrial technologies for a wide range of materials arises.Calculation studies were carried out within the framework of the thermodynamic approach to model a grinding process. In order to carry out experimental studies, a special program for measuring and processing experimental data obtained at the laboratory impact mill was developed.In the course of computational and experimental studies, a technique has been proposed to determine the energy grindability index of particulate solids. The relation of this index with the energy necessary for breakdown of the intermolecular bonds in the material under study is established.The carried out researches allowed substantiating the method of determining the generalized energy grindability index of particulate solids. Computational analysis showed that the technique with acceptable accuracy for engineering calculations can be used in practice to assess the possibility of enrichment of heterogeneous components and to determine the optimal technological conditions for the separation of these components.

Recent results of the experiments at GOL-3 facility are presented. In present configuration of the device, plasma with a density of 10 14 ÷10 16 cm -3 is confined in a 12-meter-long solenoid, which comprises 55 corrugation cells with mirror ratio B max /B min =4.8/3.2 T. The plasma in the solenoid is heated up to 2-4 keV temperature by a high power relativistic electron beam (∼1 MeV, ∼30 kA, ∼8 μs, ∼120 kJ) injected through one of the ends. Mechanism of experimentally observed fast ion heating, issues of plasma stability and confinement are discussed.