First, a simple model describes theoretically the processes involved in the irradiation of solid targets by femtosecond laser pulses and predicts the optimal target and laser parameters for efficient nanoparticles synthesis. Then, we show experimental evidence for successful synthesis of aluminum nanoparticles. Nanoparticles size distribution, morphology, atomic structure, and chemical composition are determined by various techniques, including x-ray diffraction, atomic force microscopy, scanning and transmission electron microscopy, and energy dispersive spectroscopy.

Measurements of the dynamic spall strength in aluminum, copper, and Metglas shocked by a high-power laser to hundreds of kilobars pressure are reported. The strain rates in these experiments are of the order of 10 7 s Ϫ1 , which cannot be reached in impact experiments. The free-surface velocity behavior associated with spallation is characterized by oscillations caused by the reverberations of the spall layer. An optically recording velocity interferometer system was developed to measure the free-surface velocity time history. This diagnostic method has the advantages of being a noninterfering system and produces a highly accurate continuous measurement in time. The spall strength was calculated from the free-surface velocity as a function of the strain rate. The results show a rapid increase in the spall strength, suggesting that a critical phenomenon occurs at strain rates ϳ10 7 s Ϫ1 , expressed by the sudden approach to the theoretical value of the spall strength.

Theoretical and experimental investigations of the absorption in metallic aluminum of femtosecond-laser radiation pulses with peak intensity I0 less similar 10(15) W/cm(2) are reported. Energy balance equations are solved for electron and phonon subsystems, together with Helmholtz equation for the laser radiation. Expressions for the relaxation times as functions of electron and phonon temperatures are obtained, with no free parameters. Contrary to the assumption made in published studies, we find that the interband rather than the intraband (Drude) absorption plays the dominant role in the near infrared and throughout the visible region at low and moderate intensities. For 50 fs, 800 nm laser pulses the absorption in interband transitions dominates for intensities up to few times 10(13) W/cm(2). For such pulses, broadening of the parallel-band interband absorption line with the increase in electron and phonon temperatures results, for I0 < or =5 x 10(13) W/cm(2), in the decrease of the absorption coefficient compared to the room-temperature value. In this paper, we present both the first theoretical prediction and the first experimental observation of this phenomenon. Dielectric permittivity gradients within the skin layer also contribute to the decrease in absorption. The mechanisms of the lattice disordering are considered quantitatively, and it is shown that for I0 < 10(14) W/cm(2) melting does not occur in the laser-pulse duration. Experimental results are presented for 800 and 400 nm wavelengths. The agreement between the theory and the experiment is very good.

We show numerically for continuous-wave beams and experimentally for femtosecond pulses propagating in air, that the collapse distance of intense laser beams in a bulk Kerr medium scales as 1/P;1/2 for input powers P that are moderately above the critical power for self focusing, but that at higher powers the collapse distance scales as 1/P.

Measurements of the dynamic spall strength in aluminum and copper shocked by a high power laser to pressures of hundreds of kbars show a rapid increase in the spall strength with the strain rate at values of about 107 s−1. We suggest that this behavior is a result of a change in the spall mechanism. At low strain rates the spall is caused by the motion and coalescence of material’s initial flaws. At high strain rates there is not enough time for the flaws to move and the spall is produced by the formation and coalescence of additional cavities where the interatomic forces become dominant. Material under tensile stress is in a metastable condition and cavities of a critical radius are formed in it due to thermal fluctuations. These cavities grow due to the tension. The total volume of the voids grow until the material disintegrates at the spall plane. Simplified calculations based on this model, describing the metal as a viscous liquid, give results in fairly good agreement with the experimental data and predict the increase in spall strength at high strain rates.

The approach to the ultimate strength of metals is determined experimentally. The ultimate strength of metals was calculated using a realistic wide-range equation of state. The strength of metals was measured using shock waves created in aluminum and copper foils with a short- (20–100 ps) pulse high-power laser. The strength of the materials was determined from the free-surface-velocity time history, which was measured with an optically recording velocity interferometer system. The strain rates in these experiments were in the range (1.5–5)×108 s−1.

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Highly energetic electrons are generated at the early phases of the interaction of short-pulse high-intensity lasers with solid targets. These escaping particles are identified as the essential core of picosecond-scale phenomena such as laser-based acceleration, surface manipulation, generation of intense magnetic fields and electromagnetic pulses. Increasing the number of the escaping electrons facilitate the late time processes in all cases. Up to now only indirect evidences of these important forerunners have been recorded, thus no detailed study of the governing mechanisms was possible. Here we report, for the first time, direct time-dependent measurements of energetic electrons ejected from solid targets by the interaction with a short-pulse high-intensity laser. We measured electron bunches up to 7 nanocoulombs charge, picosecond duration and 12 megaelectronvolts energy. Our ’snapshots’ capture their evolution with an unprecedented temporal resolution, demonstrat- ing a significant boost in charge and energy of escaping electrons when increasing the geometrical target curvature. These results pave the way toward significant improvement in laser acceleration of ions using shaped targets allowing the future development of small scale laser-ion accelerators.