The applicability of hydrodynamic models for theoretical description of UV laser ablation of polymers is studied. The plume formation is considered as a first-kind phase transition. In case of strongly absorbing polymers this phase transition occurs as a surface evaporation, and in case of weakly absorbing polymers as a bulk evaporation. The vapor plume is assumed to be transparent for laser radiation, and its expansion is described by the isoentropic hydrodynamic equations. New analytical expressions for ablation (etch) depths per pulse are obtained, which are in good agreement with the available experimental data (Afanasiev et al. 1997).

The experiments to study the indirect drive targets' dynamics in a highly symmetrical X-radiation field were performed on the ISKRA-5 facility. This paper covered the results of experiments with the targets in the form of a Cu spherical hohlraum, the internal surface of which is coated with Au, with six holes for laser radiation input. In the center of the aforementioned hohlraum, a glass capsule filled with D–T gas was placed. In several experiments, the central capsule was coated with an ablator made of plastic with a different thickness. This allowed us to perform a series of experiments in which the different compression degree of D–T fuel was achieved. The analyses of experimental results revealed good agreement between the latter and the spherically symmetrical hydrodynamic calculations.

Two shells with the diameter of 0.8–0.9 mm and a wall thickness of ≅1 μm were produced at the Lebedev Physics Institute for the experiments conducted at the ISKRA-5 facility. The results of two experiments with the aforementioned shells conducted at the ISKRA-5 facility with the use of an indirect-drive set up. In one of the experiments, the diameter of the golden hohlraum was D = 2 mm while in the other it was D = 4 mm. In these experiments it was observed to be ≅4 times the difference of the average laser intensity on the hohlraum surface. The results of computational analysis of the experiments are also presented here.

The investigations of the influence of various types of wavefront distortions, varying in time, on the intensity distribution on the surface of a target are carried out. It is shown that distortions of a wavefront, equivalent to transverse displacement in time of a beam in far field at an angle of approximately 10 diffraction angles, results in practically full smoothing of a specl-structure of intensity distribution. Creation of phase distortions of a beam assigned as running in a cross section wave with an amplitude of more than 3 radian and with a spatial size exceeding 20–30 times the size of the kinoform phase plate element, permits us to reduce the depth of modulation in distribution of intensity in far field also. The capability of application is considered as a smoothing device of the dynamic plasma layer, based on the volume-structured medium. The model of energy transport process in such media is developed. Matching of calculation and experimental results is conducted.

Electromagnetic emission at the plasma frequency ωp and its harmonics nωp has been studied. Although such emission is well known from very low density plasmas (electron density of the order of ne ≈ 108 cm−3) now, for the first time it has also been observed from a high density plasma (electron density of the order of ne ≈ 1023 cm−3) produced by a high-intensity femtosecond laser pulse. This radiation is strongly connected to jets of high energy electrons produced in such steep gradient plasmas by collective mechanisms, and probably to nonlinear Langmuir waves in the overdense plasma region. Theoretical investigations using particle-in-cell simulations have been made to pinpoint the physical origin and properties of the emission. Preliminary results show a very weak scaling of the ωp and 2ωp emission with intensity, which should provide clues for future theoretical analyses. Although not the main subject of the present work, also harmonics up to the 20th of the laser fundamental may have been observed close to the ωp and 2ωp line emission in the present experiment (PACS numbers: 52.40.Nk, 42.65.ky, 52.65.-y, 33.20.Ni, 52.25.Qt).

Results of turbulent mixing research of thin Al and Au layers under laser acceleration of the three-laser targets Si/Al/Au are presented. Analyses of experimental data under the program SND-TUR, where the Nikiforov model is used for turbulent mixing description, testify to the essential impact of hot spots on the examined processes in distribution of laser radiation intensity on the surface of the target. Experimental setup on the laser beams' smoothing by the “foam” coated on the target, has been considered. The results of the first experiments are presented.

In the present study we performed an experimental investigation of the Rayleigh–Taylor instability (RTI) in a mixing zone between two gases entrapped into accelerated motion by a nonstationary compression wave. Acceleration g was ∼1.5·107 cm/s2, Atwood numbers ranged from 0.04 to 0.77. A mixing zone was formed by an oxygen-hydrogen mixture and an inert gas (Ne, Ar, Kr, Xe) or SF6. The initial gas pressure was 0.5 atm. A specific feature of our experiment is compressibility of media tested and initially continuous interface between gases of different densities. The present work is a continuation of investigations on nonlinear, transition, and early turbulent stages of the RTI.

In this work, the Saha equation is solved using atomic data provided by means of analytical potentials to calculate the ionization state and ion abundances for local thermodynamic equilibrium (LTE) plasmas of Al, Fe, and Au. The plasma effects are taking into account using an analytical potential which includes plasma effects. The problem of the cut off partition functions in the Saha equation is also analyzed using three different criteria. Finally, some opacity calculations are performed.

Presently, a great part of the attention paid to the studies on the Richtmyer–Meshkov instability (RMI) is focused on the case of shock passage through a system of gas layers of different densities. The interest to this problem has been induced, in particular, by multiple attempts to minimize the process of mixing between the layers of different densities in targets for inertial confinement fusion (ICF), caused by excitation of the RMI on the layer boundaries. The RMI suppression is one of the most important, but difficult problems in worldwide efforts on ICF. A direct investigation of this phenomenon in laser experiments (in NOVA, for example) is a rather difficult task. Shock tubes are a more promising tool for modeling the impulsively-driven instabilities in gas layers, for they allow us a detailed investigation of the mechanism of initiation and the pathways of evolution of the instability (Jacobs et al. 1995; Aleshin et al. 1995a). A series of shock-tube experiments for the shock passage through a system of gas layers of different densities has been carried out. The effect of a suppression of the RMI has been found. A 2.5-fold reduction of the mixing region thickness in the presence of the layer as compared to the thickness without it has been obtained.

Holographic methods developed to study the behavior of surfaces shocked by high power lasers are reported. Shock waves of the order of hundreds of kilobars are generated in Sn targets 50-μm thick, by a Nd:YAG laser system with a wavelength of 1.06 μm, a pulse duration of 7.5 ns FWHM, and irradiance in the range (1.0–2.6)·1013 W/cm2. Two configurations of off-axis holography were applied: holograms based on forward scattering, and holograms of both backward and forward scattering. The hologram is produced by scattering of a pulse, 6.7 ns (FWHM), of green laser light synchronized with the laser that generates the shock wave. Holograms of the topology of the rear surface of shocked Sn targets moving in vacuum and in air (at atmospheric pressure) are reported.

Recently much attention has been paid to multilayer inertial confinement fusion (ICF) targets, among them the targets with low-density layers. This allows one to get a number of interesting results using the presently existing and future facilities. This concerns the volume absorption of the laser radiation in a porous matter of the density higher than the critical plasma density, and the formation of the radiation absorption region under condition of increasing geometric opacity of the low-density matter. We consider the low-density foams, 3D nets, free-standing “snow-like” layers, and pseudo low-density layers. We use artificial foam as a convenient model to allow easier comparison of the experimental laser shot data and the simulation. The requirements to such layers are also analyzed. The methods of precision control of the low-density targets are discussed.

High intensity fs-laser pulses can deliver focused intensities in the region of 1016–1019 W/cm2. If the laser pulse is focused onto a solid or gaseous material, a plasma is created. The electrons, as well as the ions are accelerated in the strong laser field up to energies in the range of keV to several MeV. The interaction of the high energy particles with cold material, that is, the solid target yield of intense X-ray emission, K-shell—as well as bremsstrahlung-radiation. The K-shell emission from layered targets is a useful indicator of the production efficiency, energy distribution, and transport of hot electrons produced in fs-laser plasmas. For the diagnosis of laser plasma interaction and its application as an intense X-ray source, the spatial, temporal and spectral distribution of K-shell X rays is of fundamental importance. Focusing crystal spectrographs can be used to obtain a single shot X-ray spectra of laser plasmas produced by table top fs-lasers. With a spatial- and spectral-focusing spectrograph based on a toroidally bent crystal, the emission region of the hot plasma and Kα-radiation can be determined. Recording the spectra online by a frontside illuminated charge-coupled device (CCD) allows alignment of the crystal spectrograph, as well as the laser beam focusing leading to different X-ray source sizes. Using a controlled fs-prepulse, an increase in Kα radiation could be observed with the diagnostic.

Measurements of calibrated high resolution spectra are compared with particle-in-cell (PIC) calculations of the laser absorption and hot electron production postprocessed by a Monte–Carlo (MC) transport model of electron stopping and Kα X-ray generation.

A whole family of laser-plasma interaction experiments is based on the phase analysis of the laser pulse after the propagation in a plasma. Typically, this phase is obtained by means of interferometry. As pulsed interferometry is a much more difficult task than taking simple images of the beam, we developed a numerical code for extracting phase information from images. The technique, based on the algorithm of Gerchberg–Saxton, showed to be very effective in retrieving 2D phase distributions of simulated as well as real beams. The convergence of the algorithm is fast (some minutes on a personal computer). The electronic noise in real images is intrinsically discarded by the algorithm.

Beam smoothing techniques and focused beam profile control techniques for high efficiency KrF laser fusion are reported. We have developed 1D and 2D broadband random phase (BRP) irradiation techniques. Our next idea is the combination of a laser oscillator with a wide beam divergence angle and phase plates. The wide divergence angle laser beam eliminates the speckle patterns caused by the phase plates. Well characterized focal spot patterns have been observed with the front-end pulse of the Super-ASHURA KrF laser system. Amplification experiments are on going.

A diffusion technique most commonly used for filling targets with a gas fuel. The need to minimize the tritium inventory in the fill station and to decrease the radiation damage during the fill raises a question of its thorough analyses to determine an efficient pressurization scheme for single and multilayer polymer shells. In this report, we present the results obtained in this area.

In conventional inertial confinement fusion (ICF), a high power laser system is used to compress a cryogenic target and create energy. One of the challenges for ICF cryogenics is producing the homogeneous and uniform fuel on the inside surface of a spherical polymer shell. In this report, we will discuss a conceptual approach based on freestanding targets and the results of our recent and current developments.

Determining the cryogenic target parameters with high precision calls for the development of a new direction in the area of target characterization based on microtomography methods of data processing. In this report we present our first results in this area.

The project ITEP-TWAC (Tera Watt Accumulator) being in progress at ITEP (Moscow) requires He-like ions for non-Liouvillean injection into the storage ring to accumulate ≈2·1013 particles with medium masses up to 59Co25+. Powerful lasers were found to be the best choice for those ions production. This work presents the experimental results of highly charge ion generation in plasmas produced by the second harmonic of Nd-glass laser facility with a total energy E ≤ 50 J and pulse duration of about 2.5 ns at GPI (Moscow). Ti and Ta targets were under investigation. An electrostatic ion energy analyzer and an ion charge collector were used to measure the ion charge state spectra at a 3-m distance from the targets. 5·107 He-like Ti ions per cm2 within 1 μs pulse as well as 107 Ta+41 per cm2 within 0.8 μs were observed.

The results of numerical simulation of the neutron generation process in the cone lead targets exposed to laser irradiation are presented. The experimental time dependence of the target shell is used as a boundary condition for the hydrodynamic equations. Deuterium compression is calculated on the assumption that some part of the shell that continues to move inward onto the conical target is decelerated by deuterium in the absence of the reactive force. The behavior of deuterium is described by the 2D equations of two temperature gas dynamics with the electron and ion contributions to the heat conduction taken into account. The behavior of lead is described by the 2D equations of gas dynamics closed by the real wide range equation of state (EOS). The neutron yield in the experiments under discussion is caused by short duration steep rises of the ion temperature generated by the collapse of the heading shock wave and the first reflected one. The stage of adiabatic compression of the high-temperature plasma was lacking in the experiment due to the small mass of the shell.

Two series of experiments on laser irradiation of the different thickness Al-foils were made using laser facilities “GARPUN” and “PICO” (Lebedev Physical Institute, Moscow). “GARPUN” is the KrF-laser with pulse energy Elas ≈ 100 J and pulse duration τ ≈ 100 ns. “PICO” is a Nd-laser facility. The laser energy is Elas1 ≈ 20 J and τ ≈ 3–4 ns in a single beam. The burn through time (tb) of different thickness foils was studied. We have varied the foil thickness: d = 20–500 μm for “GARPUN” facility experiments, and d = 3–12 μm for the case of “PICO” experiments. It was discovered that the rates of the foil burn through are much higher than those obtained in (Dahmani et al., 1991a,b). The experimental data were analyzed with the help of 2D numerical simulations, using the 2D Euler code “NUTCY.” Good agreement was obtained between numerical and experimental results. In the first case the rate of foil “enlightment” is defined by transversal displacement of matter (“drilling effect”). With allowance for the effect of “hot spots formations” it was possible to explain the burn through of thick foils and low laser energy at the rear side of films in “PICO” facility experiments (“microdrilling effect”). The methods of the diminishing of the influence of microdrilling effect (or “imprint” effect) on the nonuniformity of ablation pressure are discussed.