Igor K. Krasyuk

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.

Study of extreme states of matter at high energy densities and high strain rates with powerful lasers

In the paper, a review of most important results of experimental studies of thermonuclear plasma in conical targets, generation of shock waves and spallation phenomena in different materials, which were carried out at laser facilities of the A M Prokhorov General Physics Institute RAS since 1977, is presented.

Experimental verification of the ablation pressure dependence upon the laser intensity at pulsed irradiation of metals

Experiments for verification of a functional dependence of the ablation pressure on the irradiated surface of a target upon the laser intensity in a range from 1.2 to 350 TW/cm2 have been carried out. For that, at some intensities of the laser irradiation, time intervals between the laser pulse maximum and the moment of the shock-wave front arrival to the rear surface of the target were measured, which are dependent on the ablation pressure. Two schemes of the measurements were used. At the first scheme, at higher laser intensities, the front arrival moment is determined via an electron-optical camera when the rear surface begins glowing. At the second scheme, the front arrival moment is recorded when a probe laser pulse changes the character of the reflection by the rear surface of the irradiated target. Results of measurements are in agreement with the ablation pressure dependence upon the laser pulse intensity within 20%.

Experimental investigation into polycrystalline and single-crystal diamonds under negative pressures formed by picosecond laser pulses

Results of the experimental investigation of the spallation phenomenon in polycrystalline and single-crystal synthetic diamond are presented. The shock-wave action on the target was formed by a laser pulse with a duration of 70 ps using a Kamerton-T installation. To attain the ablation pressure of 0.66 TPa on the face surface of the target, the laser radiation of the Nd:glass laser (second harmonics λ = 527 nm, the pulse energy is 2.5 J) was used at intensity up to 2 × 1013 W/cm2. The attained maximal spall strength of diamond σ* ∼ 16.5 GPa is 24% of the theoretical ultimate strength. The Raman scattering indicates that a small amount of crystalline diamond is graphitized in the spall region on the back target side.

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.

Specific features of the application of a laser interferometer in the study of shock-wave phenomena

The application of a laser interferometer for the detection of the motion of the free surface of a target induced by the subnanosecond shock-wave action is analyzed. It is demonstrated that reliable results can be obtained only with regard to the response function of the interferometer.

A double-pulse laser oscillator with a continuously variable time interval between the pulses

A description is given of a possible method for obtaining two synchronized laser pulses, separated in space and time. The system proposed provides a continuously variable time interval between the laser pulses (of energy 0.3 J and pulse length 25–50 nsec) over the range 0–15 μsec, and it can be used for synchronizing the triggering of various devices and photographic recording of objects and processes over a wide time interval.