We analyze the results of a recent experiment performed at the PALS laboratory and concerning ablation pressure at 0.44 µm laser wavelength measured at irradiance up to 2 × 1014 W/cm2. Using the code “ATLANT,” we have performed two-dimensional (2D) hydrodynamics simulations. Results show that 2D effects did not affect the experiment and also give evidence of the phenomenon of delocalized absorption of laser light.

Hot electrons may significantly influence interaction of ultrashort laser pulses with solids. Accurate consideration of resonant absorption of laser energy and hot electron generation at a critical surface was achieved through the developed physical and mathematical models. A two-dimensional (2D) ray-tracing algorithm has been developed to simulate laser beam refraction and Bremsstrahlung absorption with allowance for nonlinear influence of a strong electromagnetic field. Hot electron transport was considered as a straight-line flow weakening by a friction force calculated in the approximation of the average state of ionization. Developed models were coupled with the 2D Lagrangian gas dynamic code “ATLANT” that takes into account nonlinear heat transport. The developed program has been applied to simulate irradiation of Al foils by picosecond laser double pulses. Hot electron transport and heating resulted in thin foil explosions. The transition from the exploding foil regime to the ablative one with foil thickening has been simulated and analyzed at various values of laser light intensity. In second series of calculations we have modeled the interaction of a nanosecond iodine laser with a two-layered target.

The electron-beam-pumped KrF laser installation GARPUN with a 100-J output energy and long 100-ns pulse duration has been used to investigate laser–target interactions in a broad range of laser intensities for small (150 μm) and large (∼1 cm) irradiated spots. For higher intensities (up to 5 × 1012 W/cm2), a conical shock wave was generated in condensed matter by megabar pressure at the ablation front. It propagated with a supersonic velocity in a quasisteady manner together with a conical shock wave inside a target. Evaporated target material moving with a velocity of ∼50 km/s formed an extended plasma corona of ∼5 mm length with an electron temperature of ∼100 eV. Emission spectra of plasma have been investigated in the extreme UV range 120–250 Å. For lower intensities (108–109 W/cm2), planar shock waves in normal density air were produced with initial velocities up to 4 km/s in the forward direction and 7 km/s in the opposite direction toward incident radiation. In rarefied air, the forward shock wave kept velocities constant whereas the backward ones were accelerated up to 30 km/s. Planar compression waves in transparent condensed matter were also demonstrated propagating with sonic velocity.

Formation of transverse inhomogeneities in the corona of a solid target irradiated by an inhomogeneous main laser pulse and a uniform background pulse was observed experimentally via side-on shadowgraphy. The experimental results were successfully interpreted using a two-dimensional hydrodynamics code. Our simulations identified the onset of sharp contact boundaries between plasma streams of different expansion velocities. The formation and the decay of the contact boundaries is investigated in detail. When the background pulse is used as a laser prepulse, a layer of coronal plasma is formed that enhances main pulse collisional absorption in underdense plasma and creates conditions for an efficient thermal smoothing of the transverse inhomogeneities.

Laser prepulse effect on thermal smoothing of non-uniformities of target illumination is studied by means of 2D Lagrangian hydrodynamics simulation, based on parameters of real experiment. A substantial smoothing effect is demonstrated in case of an optimum delay between the prepulse and main heating laser pulse. The cause of enhancement of thermal smoothing effect by laser prepulse is the formation of long hot layer between the region of laser absorption and ablation surface. Comparison with experimental results is presented.

A possibility of input of high-power laser pulse into a cavity through a hole was studied by means of 2D numerical calculations. Such tasks appear in view of investigation of the effective targets with internal input of energy (Bessarab et al. 1992; Basov et al. 1998), “cannon-ball” (Hogan 1989), “Greenhouse” targets (Gus'kov et al. 1995).

We have used two Euler codes “NUTCY” and “FAKEL” to model the problems of laser beam input into a cavity through the holes.

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.

The results of the experiments at the installation “PICO,” with thin foils heating by laser radiation pulses of nanosecond duration are reported. The Al foils with thickness in the range from 3 μ up to 40 μ were used as targets. The flux density was varied from 1013 W/cm2 to 1014 W/cm2. The sharp dependence of the portion of laser energy that passed through the target on foil thickness was observed. This phenomena was accompanied by a relatively small decrease of the passed radiation pulse duration. The anomalously high speed burning through of thin foil was observed in these experiments and the conclusion on the possible mechanism of this phenomena has been done on the base of comparison of experimental data with theoretical calculations. The observed phenomena can be interpreted with a conjecture about the local burning through of a target, in the small areas of the target surface, with many more values of flux density than the average one following laser radiation self-focusing and formation of “hot spots.”

Multistage, e-beam-pumped, 100 J-class KrF laser installation “GARPUN” is described with the emphases to high-power laser beam control and target irradiation experiments. The ablation pressures in the megabar range were measured and hydrodynamic flow was investigated both experimentally and by numerical simulations for laser intensities up to 5×1012 W/cm2, pulse duration of 100 ns, and focal spot diameter 150 μm. Graphite-diamond phase transformation under laser loading was observed by dynamic and Raman scattering methods. Some approaches to the fast ignition inertial confinement fusion, using the simultaneous amplification of long and short laser pulses in KrF drivers, are considered.

A physical-mathematical model for the development of the boundary instability of a spherical incompressible-liquid shell, with due regard for the ablation effect, is considered.

The development of hydrodynamic instability (HDI) in laser targets is studied by means of 2D numerical code “ATLANT.” The scaling of HDI development for the condition of “DELFIN-1” laser setup experiments is derived. It is shown that there is the possibility to improve the shell compression condition for the case of long-wave perturbation of laser flux (determined by particular target irradiation geometry) by using the shell with “relief.”