We have studied a suite of cylindrical, polystyrene targets, both unperturbed and with mode-28, 1.5 μm initial-amplitude sinusoidal perturbations imposed azimuthally along the target length. All targets are driven by direct laser illumination at 3ω using the University of Rochester OMEGA laser facility. Our numerical simulation and experimental data demonstrate the proof of principle for direct-drive studies of complex hydrodynamic phenomena in convergent geometry. We obtain high-quality, time-dependent data, that demonstrate good implosion symmetry and against which numerical simulations show promising agreement within currently assessed error bars. Our results identify operational space for continuing experiments.

Irregularities on the outer surface of Inertial Confinement Fusion (ICF) capsules accelerated by laser irradiation are amplified by the Rayleigh–Taylor instability (RTI), which occurs at the ablation front (ablative RTI), where density gradient and acceleration have the same direction. The analytic stability theory of subsonic ablation fronts, for Froude number larger than one, shows that the main stabilization mechanisms are blowoff convection (rocket effect equilibrating the gravity force) and ablation (Sanz 1994; Betti et al. 1996). Blowoff convection and ablation are enhanced if the ablator material is mixed with high-Z dopants. The latest enhances radiation emission setting the ablator on a higher adiabat, lowering its density, and increasing the ablation velocity. When such an ablator is used to push a solid deuterium-tritium (D–T) shell, the D–T-ablator interface becomes classically unstable. The aim of this paper is to investigate the stability of such a configuration, represented by a low-density ablator pushing a heavier shell, and study the interplay between the classical and ablative RTIs occurring simultaneously. The stability analysis is carried out using a sharp boundary model (Piriz et al. 1997), which contains all the basic physics of the RTI in ICF.

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.

The field of diffractive optics is at the same time old and young. Diffraction gratings have been known for two centuries and used extensively in spectroscopy, for example. Also the theoretical understanding of the basic properties of grating diffraction has been well developed since that time. Until the 1960s, the technological foundation of grating manufacture used to be precision mechanics. It was then, when with the advent of the laser, things gradually started to change. On the one hand, laser interferometry became an additional tool to fabricate grating structures with very small periods. On the other hand, many new applications for optics started to develop based on the use of different types of laser sources. Some examples that may be mentioned are—besides modern spectroscopic techniques—areas like material processing, optical communications and information processing, optical data storage, etc. Consequently, the term “diffractive optics” has obtained a different flavor during the past 20–30 years. New types of diffractive elements were being developed with new technologies. This started in the mid-1960s with the invention of computer-generated holography which allowed to create “arbitrary” wavefronts (this means, within practical limits) by diffracting a light wave at an irregular binary structure. The computation and fabrication of computer-generated holograms was made possible by then newly available digital computers and plotting equipment. Since the early 1970s, people started to make diffractive elements using microfabrication techniques (lithography, etching, etc.) adapted from the processing of electronic circuits. These ideas were initially demonstrated in industrial research laboratories like Philips and Thomson-CSF.

Modification of the growth of scattering processes in the case of multiple beam irradiation compared to single beam irradiation has been investigated in a preformed plasma using Thomson scattering of a short wavelength probe beam, and spectral and temporal analysis of reflected and transmitted light. First observations of the reduction of the amplitude of ion acoustic waves associated with simulated Brillouin scattering, amplification of the amplitude of electron plasma waves associated with stimulated Raman scattering, and transfer of energy between crossing beams with same frequency in a flowing plasma under crossed beam irradiation are reported.

In this paper, we want to discuss different hydrodynamic schemes for fast ignition and some of their basic effects. Relativistic hydrodynamics and a covariant generalized Ohm's law are presented. Matter perforation (hole boring) by an intense laser pulse is investigated by 2D numerical simulations and a simple formula for the perforation speed is derived. Furthermore, we study macroparticle acceleration by an intense laser beam and the possibility to provide an energetic and massive projectile for ballistic ignition. The dynamics of ignition of a precompressed D–T mixture is illustrated by numerical simulations in planar 2D geometry using direct laser irradiation and macroparticle impact as external drivers. Electron heat conduction is found to be responsible for an efficient burn wave propagation which prevents the hot gas bubble of burning fuel from deflagrating into vacuum.

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 time-resolved X-ray conversion efficiency campaign was conducted at CEA/Limeil–Valenton on the PHEBUS laser, with Au planar targets. The calibrated diagnostic DEMIXART has measured X-ray emissions driven by shaped laser pulses. The results have been analyzed with the “physicist” 1D1/2 hydrodynamical code CHIVAS, where improved transport coefficients have been implemented. The influence of the degeneracy and solid/liquid corrections on various parameters is shown. Other significant effects due to focal spot shapes and lateral conduction are quantified with the FCI2 hydroradiative code of CEA/DRIF.

Experimental results of heating measurements of matter carried out in a study of laser-driven shock waves in aluminum (Batani et al. 1997) are discussed. The measured temporal evolution of the “color” temperature of the rear surface of the target is compared with that computed by a numerical code. It has been established that the target preheating can substantially affect optical signal features recorded from the rear side of the target, and consequently influence upon the accuracy of temperature and pressure measurements of the material behind the shock wave front.

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.

Hydrodynamic instabilities, such as the Rayleigh–Taylor and Richtmyer–Meshkov instabilities, play a central role when trying to achieve net thermonuclear fusion energy via the method of inertial confinement fusion (ICF). The development of hydrodynamic instabilities on both sides of the compressed shell may cause shell breakup and ignition failure. A newly developed statistical mechanics model describing the evolution of the turbulent mixing zone from an initial random perturbation is presented. The model will be shown to compare very well both with full numerical simulations and with experiments, performed using high power laser systems, and using shock tubes. Applying the model to typical ICF implosion conditions, an estimation of the maximum allowed target, in-flight aspect ratio as a function of equivalent surface roughness, will be derived.

We are working on the generation of the high-power UV pulse by backward Raman pulse amplification. This report deals with the generation of the high-power backward first Stokes light using a simple focusing geometry. The high-power Stokes light, which grows from spontaneous scattered light in the focal region, can be obtained by focusing the high-energy KrF pump pulse into a Raman cell filled with methane gas. The intensity of the pump pulse increases significantly near the focus. This pulse produces a serious effect of the nonlinear refractive index. We mixed xenon gas into the Raman medium to compensate for this effect. As a result, a stable generation of the high-power single backward first Stokes light can be obtained.

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.

The frequency-doubling efficiency and resultant focal spot quality of a large aperture (140 × 89 mm) subpicosecond, chirped pulse amplified (CPA) 1054-nm beam for laser–matter interaction studies has been investigated using the Vulcan Nd:glass laser system (Danson et al. 1998). The effect of B-integral on the CPA beam quality was studied and is shown not to be the dominant cause of the observed frequency-doubled beam break-up. Conversion efficiency tests were carried out on small aperture KDP (type 1) crystals at a range of incident intensities up to 3 × 1011 W/cm2 giving the optimum crystal thickness for pulses in the 0.3–3 ps region. A large-aperture frequency-doubled beam was commissioned and delivered pulses of over 10 TW onto target for an electron acceleration experiment.

Targets of thin (0.1 μm) Al buried beneath 0.1 μm plastic overlay have been irradiated by the 350 fs CPA pulse from the 248 nm Titania KrF laser at irradiances of 1017 W/cm2. We report a study of the radiative properties of the Al plasma using X-ray emission spectroscopy. It is demonstrated that short-pulse irradiation of buried-layer targets can produce a plasma with close to solid densities and electron temperatures of several hundred eV. We examine the effect that a long duration (5–50 ns) low intensity (∼5 × 108 W/cm2) prepulse has on the measured values of electron density and temperature. The experimental technique will allow the determination of the accuracy of LTE radiative calculations in this new regime of extremely high material energy density.

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.

Experimental study of the radiation scattered at the laser heating of low-density foam targets and transmitted through the targets is presented. The scattered and transmitted radiations were investigated using spectrometers and streak cameras providing spatial, angular, spectral and temporal resolutions that enabled us to study the dynamics of the process of burning-through of the thick foam targets, the velocities of the plasma critical density motion as well as mass velocity of the plasma.

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.

Since 1973, research into the problem of laser thermonuclear fusion has been carried out at VNIIEF. For this purpose, laser iodine facilities ISKRA-4 and ISKRA-5 with the peak radiation power up to 100 TW have been created. In the present work, the main stages of these facilities creation, approaches to the selection of the pumping sources, working media, optical scheme, radiation focusing system, the system of the pumping sources energy feed, laser radiation, and plasma parameters diagnostics methods are shown. There are also presented types of the targets, filled with DT-gas, in which the high temperature plasma is formed and its parameters are studied. Data on values of neutron yield, of X rays in wide energy range, degree of implosion, and data on mix of heavy and light layers of matter are presented as well.

Measurements of spectral and energy X-ray characteristics of almost transparent Fe plasma produced by laser radiation inside the inverted-corona targets have been made at ISKRA-5 facility. The targets were spherical plastics cavities with 2-mm diameter and 4.6-μm thickness covered from inside with Fe layer 0.25-μm thickness. X-ray spectrum, X-ray total energy, and the energy of a HeαFe resonance line have been measured. Experimental data and calculation results are collated.