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The population kinetics of a two-level system has been theoretically investigated taking into account the transfer of spontaneous radiation under continuous optical pumping. It is shown that, when the photon mean free path in a resonantly absorbing medium is smaller than the characteristic size of this medium or comparable to it, the spontaneous radiation may become an additional pump source. The contribution of spontaneous photons to the kinetics of level has been considered within two approaches. The first approach consists of solution of the radiation transfer equation within the diffusion approximation. The second approach is related to solution of the Biberman–Holstein equation.

We present the results of our experiments at the Luch laser facility in which the processes of the destruction of iron asteroids and cometary nuclei in space by nuclear explosions on their surface are simulated based on the principle of physical similarity. We present the results of our numerical simulations of impacts on the surface of iron objects confirming the similarity of the key processes in the full-scale and model cases. The technologies of fabricating miniature mockups with parameters close to those of iron asteroids and cometary nuclei are described. For various mini-mockups 3–12 mm in size at a laser energy from 50 to 450 J we provide an experimental estimate of the energy threshold for the undeniable destruction of mockups and investigate the parameters of their fragmentation. Conclusions about the probable results of the impact of a nuclear explosion on hazardous cosmic objects have been drawn.

We report on the results of experiments performed on the Iskra-5 laser facility for studying the effect of the polydeuteroethylene (CD2)n working layer thickness on the operation parameter of an inverted-corona target. In all experiments of this series, the neutron yield at a level of 107–3 × 108 DD neutrons per shot was detected for the total laser radiation energy supplied to the target by 12 second-harmonic beams in the range of 1.6–2.2 kJ. Using the neutron time-of-flight technique, we have detected an increase in the ion temperature from approximately 6.4 to 14 keV upon a decrease in the (CD2)n layer thickness from 1 to 0.1 μm.

We present the results of preliminary experiments at laser facilities in which the processes of the undeniable destruction of stony asteroids (chondrites) in space by nuclear explosions on the asteroid surface are simulated based on the principle of physical similarity. We present the results of comparative gasdynamic computations of a model nuclear explosion on the surface of a large asteroid and computations of the impact of a laser pulse on a miniature asteroid simulator confirming the similarity of the key processes in the fullscale and model cases. The technology of fabricating miniature mockups with mechanical properties close to those of stony asteroids is described. For mini-mockups 4–10 mm in size differing by the shape and impact conditions, we have made an experimental estimate of the energy threshold for the undeniable destruction of a mockup and investigated the parameters of its fragmentation at a laser energy up to 500 J. The results obtained confirm the possibility of an experimental determination of the criteria for the destruction of asteroids of various types by a nuclear explosion in laser experiments. We show that the undeniable destruction of a large asteroid is possible at attainable nuclear explosion energies on its surface.

This paper presents the results of computational–experimental studies of the laser heating of carbon (graphite) particles having a size of about 500 μm, located on a quartz substrate in inert nitrogen and argon media in the intensity range of laser radiation from 0.35 to 3.5 kW/cm2. The temperature of the particles is experimentally measured in the field where the laser radiation acts. It is shown that heating the carbon particles damages the surface of the quartz substrate in virtually the entire zone of the laser spot, with the formation of a crater whose center coincides with the center of the particle. The LOGOS software package, developed at the Russian Federal Nuclear Center—All-Russia Scientific Research Institute of Experimental Physics, is used to numerically model the process by which the laser radiation interacts with the carbon (graphite) particle lying on the quartz substrate. The results indicate that a chemical reaction occurs between the carbon and the quartz with possible formation of a layer of silicon carbide on the substrate surface.

An investigation was made of fuel films in targets used in experiments on laser thermonuclear fusion in Iskra-4 and Iskra-5 systems. These films were formed from condensed deuterium and a deuterium—tritium mixture, and also from metal hydrides and polyethylene containing deuterium and tritium.

It was found experimentally that after breakdown of Q-switched Nd-YAG laser beam in noble gases the toroidal radiative formations shaped from initial spherical region of hot luminous gas. Schlieren and interferometric examinations reveal the existence of nonuniformity in energy input at early spark stage and following formation of the whirl ring structure after the produced shock wave has gone away. The results of numerical modelling of gas dynamical flow arising in Ar after inhomogeneous energy input imitating laser breakdown in real conditions are in qualitative agreement with the observed picture.

A numerical investigation is made of the nonlinear stage of development of the Kelvin-Helmholtz instability in the case of compressible gases.