ИТФ им. Л.Д. Ландау L.D.Landau ITP RAS

Plasma & Lasers (Рус)

Scientific research

  1. Interaction of laser radiation with matter
  2. Extreme states of matter
  3. Hydrodynamic instabilities

Interaction of laser radiation with matter

Important place in the work of the sector is the study of interaction of laser radiation with condensed matter. Currently, the most interest is the impact on the condensed targets (metals, dielectrics, semiconductors) ultrashort femtosecond pulses. Such small duration of the laser pulse leads to the distinctive features in the ablation (entrainment of matter from the surface of the target). In the sector for the first time a detailed study of the structure of the ablation plume. arising from exposure to femtosecond laser pulses on metals. Showed the presence of a shell of a condensed phase of metal separated from the crater in the target two-phase mixture of condensed matter and steam. It is possible to explain the observed in the experimental study of laser ablation optical phenomena, in particular, the system of Newton's rings. Able to explain the specific form of craters at a femtosecond pulse of metal targets, multiple thresholds for the value paverhnostnoy energy density (the melting threshold, threshold ablation threshold evaporation), near which dramatically changes the nature of the interaction of radiation with matter. To study the structure of ablation used hydrodynamic calculations and molecular dynamics simulation. In the hydrodynamic approach, the most adequate in the early stages of laser pulse interaction with the target material, it is considered distinct electron and ion temperatures in strongly nonideal metal high density corresponding to condensed matter, and used a two-temperature hydrodynamic equations, including electronic and ionic conductivity and the energy exchange between the electron and ion subsystems. Molecular dynamics simulation, performed with the assistance of parallel computing, held for the maximum possible at the present time the number of particles involved in the simulation (up to several hundred million). In addition, for the interaction of particles of the target material used as paired interparticle potentials and most well describe many-particle potentials of the metal. Conduct such calculations can now only a few research groups in the world. For the first time calculated the ablation of a metal target (aluminum) with the simultaneous use of hydrodynamic and molecular dynamics approach in which the parameters of the target state, obtained at an early stage of hydrodynamic are the initial data for the subsequent expansion of the molecular dynamics of the target material, which allows the most accurate research arise in this phase transitions and structure of the multi-phase ablation cloud. Theoretical study of the interaction of laser radiation with solid targets is in close collaboration with experimental studies, in particular, to the experiments carried out on a unique laser system for chromium-forsterite with a pulse duration of 40-100 fs in RAS. Used "pump-probe" scheme of optical diagnostics can monitor the evolution of the state of the target material with a time step of 100 fs and achieve the best accuracy is in finding the reflection coefficient (~ 1%) and measuring the phase of the reflected beam dignosticheskgo (~ 1 nm for the difference of the rays) . This laser system and diagnostic technique successfully used to study the action of ultrashort laser pulses at a target made of fused metals and semiconductors.

Extreme states of matter

The study of matter at high values ??characterize its thermodynamic parameters, such as pressure and temperature, as well as strong external fields, is important. This is an important aspect, in particular, astrophysical research. The development of experimental techniques can create more and more high pressure, temperature and strong external fields on Earth. Thus, there is considerable progress in creating an extremely high pressures, megabar range, compressive material in a diamond anvil cell. Obtained in this high pressure are static in nature, that while improving diagnostic techniques, the use of, in particular, improved methods of indicating pressure diffraction techniques using synchrotron radiation to determine the structure of the material used to research various transformations occurring in the material at megabar pressures. These transformations include aggregate, a variety of structural phase transitions, phase transitions, insulator-metal transition metals in the superconducting state. Even higher pressures up to several terabar to come from non-stationary conditions explosive experiments, which allows us to study the properties of matter at these extremely high pressures. The development of lasers has led to the emergence of new sources of intense exposure to the substance, such as a laser is used to produce heat. Widely conducted experimental work to create high-power lasers with high pressure to the strong compression of matter, in particular, for inertial confinement fusion. Development of the technology of lasers ultrashort (femtosecond) pulse length range allows you to select the energy of laser radiation and raise the temperature of the substance in such a small period of time that, for condensed matter becomes possible to obtain the states with very different temperature electron and ion subsystems. Ultrashort laser pulse interaction with solids to create a unique electron-phonon states in metals and semiconductors. Study of electron and ion subsystems of condensed phases of matter under the influence of ultra-short laser pulses is very important in the interaction of intense laser radiation with matter. This problem is relevant in particular for metals in the solid phase in the study of ablation with intense laser radiation. As the parameters that have a significant influence on the thermal properties of matter, may make external field, such as a magnetic field. The study of the behavior of matter, in particular, its condensed phases in strong magnetic fields relevant for astrophysical research. Existing in astrophysical magnetic fields reach such high values ??that, together with the Coulomb interaction begin to determine the structure of atoms, thus changing the interaction between them and the thermodynamic properties of condensed phases such atoms. Smaller but steadily increasing as you progress of laser technology value of strong magnetic fields observed in the interaction of intense laser radiation with matter.

Hydrodynamic instabilities

Hydrodynamic phenomena are among the key issues in high energy density physics, astrophysics, and chemical technology. It is about the complex issues associated with the hydrodynamic instabilities and turbulent mixing. Thus, the fundamental problem is how to instabilities and turbulence in themselves and their applications in these scientific areas. In applications difficult hydrodynamic problem "acquire" many additional fundamental complications, such as requiring consideration of thermodynamics of strongly coupled plasma (inertial fusion), or the inclusion of radiation effects (astrophysics). Important place among the hydrodynamic instabilities belongs Rayleigh-Taylor and Richtmyer-Meshkov. Especially interesting are the nonlinear stage of the instability arising in this turbulent mixing of fluids. . Along with the study of turbulence in the Richtmyer-Meshkov, studies on nonlinear periodic solution of Richtmyer-Meshkov and Rayleigh-Taylor instability. These studies are important in the rapidly developing physics of neutron stars. They allow you to explore the interesting phenomenon as akretsiya, ie absorption of the surrounding material of the neutron star, to investigate the characteristics of the accretion zone on the surface of the neutron star. This zone occurs in the contact zone of the accretion disk with the surface of the star. Here we have, for example, because of the slowdown in turbulent shear flow on the high-friction surface of a neutron star (reducing the speed of the Keplerian rotation of the star to rate).

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