V. I. Vovchenko

The spall strength limit of matter at ultrahigh strain rates induced by laser shock waves

New results concerning the process of dynamic fracture of materials (spallation) by laser-induced shock waves are presented. The Nd-glass laser installations SIRIUS and KAMERTON were used for generation of shock waves with pressure up to 1 Mbar in plane A1 alloy targets. The wavelengths of laser radiation were 1.06 and 0.53 μm, the target thickness was changed from 180 to 460 μm, and the laser radiation was focused in a spot with a 1-mm diameter on the surface of AMg6M aluminum alloy targets. Experimental results were compared to predictions of a numerical code which employed a real semiempirical wide-range equation of state. Strain rates in experiments were changed from 10 6 to 5 X 10 7 s -1 Two regimes of spallation were evidenced: the already known dynamic regime and a new quasi-stationary regime. An ultimate dynamic strength of 80 kbar was measured. Finally, experiments on targets with artificial spall layers were performed showing material hardening due to shock-wave compression.

Effect of submillisecond radiation of the erbium laser on absorbing liquid

Pressure pulses occurring in water under the effect of submillisecond radiation of the Er3+:YAG laser on the free and covered liquid surface were measured. The behavior of pressure pulses is caused by the photoacoustic effect, explosive boiling of the superheated liquid surface layer, and cavitation processes developing after laser exposure.

Investigation of the dynamic fracture process at ultrahigh strain rate caused by laser‐induced shock waves in solid targets

This work consists of three main parts. In the first part dependence of amplitude of ablation pressure from intensity of laser radiation in a specified range is experimentally investigated. In the second part measurements of spall strength of a researched material from deformation rate up to 3⋅107 s−1 are performed. In the third part measurements of mechanical work, expended on separation of spall layer, are carried out.

Direct amplification of picosecond pulses in F{sub 2}{sup -} : LiF crystals

An amplifier of picosecond pulses with an output power up to 1010 W and an energy up to 30 mJ at 1180 nm is developed on the basis of F2- : LiF colour-center crystals. A 3?5-ps, 0.03-mJ probe pulse at 1.18?m was obtained upon intracavity SRS conversion in a passively mode-locked Nd3+ : KGd(WO4)2 laser. The F2- : LiF crystals were pumped by 1053-nm nanosecond pulses from a Nd : YLF laser, amplified in a GLS-22 phosphate glass to an energy of 5 J. The probe SRS pulses were amplified in a four-crystal two-cascade amplifier based on F2- : LiF crystals with the total length of the active medium of 360 mm, by using counterpropagating pump beams. The dependences of the output radiation energy on the pump and input signal energies are measured.