S. I. Ashitkov

Behavior of aluminum near an ultimate theoretical strength in experiments with femtosecond laser pulses

The dynamics of the motion of the free surface of micron and submicron films under the action of a compression pulse excited in the process of femtosecond laser heating of the surface layer of a target has been investigated by femtosecond interferometric microscopy. The relation between the velocity of the shock wave and the particle velocity behind its front indicates the shock compression to 9–13 GPa is elastic in this duration range. This is also confirmed by the small (≤1 ps) time of an increase in the parameters in the shock wave. Shear stresses reached in this process are close to their estimated ultimate values for aluminum. The spall strength determined at a strain rate of 109 s−1 and a spall thickness of 250–300 nm is larger than half the ultimate strength of aluminum.

Formation of nanocavities in the surface layer of an aluminum target irradiated by a femtosecond laser pulse

It has been revealed experimentally that nanocavities remain inside a surface layer of aluminum after action of a femtosecond laser pulse. This result is in agreement with numerical simulation. A detailed picture of melting, formation of expansion and compression waves, and bubble nucleation in the stretched melt has been reconstructed through atomistic simulation. It has been shown that the bubbles do not fully collapse but remain as frozen disk-shaped nanocavities upon recrystallization of the melt. The formation of a porous metal with small voids is very important for understanding the physics of laser exposure and may have significant applications.

Nanospallation induced by an ultrashort laser pulse

A femtosecond laser pulse with power density of 1013 to 1014 W/cm2 incident on a metal target causes ablation and ejection of the surface layer. The ejected laser plume has a complicated structure. At the leading front of the plume, there is a spall layer where the material is in a molten state. The spall layer is a remarkable part of the plume in that the liquid-phase density does not decrease with time elapsed. This paper reports theoretical and experimental studies of the formation, structure, and ejection of the laser plume. The results of molecular dynamics simulations and a theoretical survey of plume structure based on these results are presented. It is shown that the plume has no spall layer when the pulse fluence exceeds an evaporation threshold Fev. As the fluence increases from the ablation threshold Fa to Fev, the spall-layer thickness for gold decreases from 100 nm to a few lattice constants. Experimental results support theoretical calculations. Microinterferometry combined with a pump-probe technique is used to obtain new quantitative data on spallation dynamics for gold. The ablation threshold is evaluated, the characteristic crater shape and depth are determined, and the evaporation threshold is estimated.

Determination of the Transport and Optical Properties of a Nonideal Solid-Density Plasma Produced by Femtosecond Laser Pulses

Experimental data on the amplitude and phase of the complex reflection coefficient of a laser pulse from a non-ideal solid-density plasma, which is produced on the surface of a metallic target by intense femtosecond laser radiation, have been obtained using femtosecond interference microscopy. A theoretical model developed for the interaction of intense femtosecond laser pulses with solid targets on the basis of the two-temperature equation of state for an irradiated substance allows the description of the dynamics of the formation and scattering of the plasma. Comparison of the experimental data with the simulation results provides new information on the transport coefficients and absorption capacity of the nonideal plasma.

Achievement of ultimate values of the bulk and shear strengths of iron irradiated by femtosecond laser pulses

Shock-wave phenomena generated by femtosecond laser pulses in submicron iron film samples have been studied by the interferometric method with the application of frequency-modulated diagnostics in the picosecond time range. The splitting of the shock wave into the elastic and plastic waves with a compression stress of up to 27.5 GPa behind the front of an elastic precursor has been detected. The corresponding maximum shear stress reaches 7.9 GPa, which is even somewhat higher than the calculated ideal shear strength. The measured spall strengths reach 20.3 GPa, which is also comparable to the calculated values of the ideal tensile strength.

Strength properties of an aluminum melt at extremely high tension rates under the action of femtosecond laser pulses

AbstractThe dynamics of the melting of a surface nanolayer and the formation of thermal and shock waves in metals irradiated by femtosecond laser pulses has been investigated both experimentally and theoretically. A new experimental-computational method has been implemented to determine the parameters of laser-induced shock waves in metallic films. Data on the strength properties of the condensed phase in aluminum films at an extremely high strain rate (

Mechanical and optical properties of vanadium under shock picosecond loads

\dot V

Two-temperature thermodynamic and kinetic properties of transition metals irradiated by femtosecond lasers

/V ∼ 109 s−1)under the action of a laser-induced shock wave have been obtained.