A. Yu. Semenov

Problems in the optical measurement of dense plasma heating in laser shock wave compression

Experimental results on the heating of matter carried out in a study on laser-driven shock waves in aluminium are discussed. The measured temporal evolution of the `colour temperature of the rear surface of the target is compared with that computed by numerical codes. We show how the target preheating can substantially affect optical signals recorded from the rear side of the target, and consequently influence the accuracy of temperature and pressure measurements of the material behind the shock wavefront.

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%.

Investigation of the spall strength of graphite using nano- and picosecond laser pulses

Spallation phenomena in graphite targets were investigated experimentally under nano- and picosecond shock-wave action at laser facilities Kamerton-T (GPI RAS) and PHELIX (GSI). In the range of strain rates of 1 to 10 μs−1 at the first time, data of dynamic tensile strength of the material were obtained. At maximal realized strain rate of 14 μs−1, the spall strength value 2.1 GPa has been achieved that is 64% of the theoretical ultimate tensile strength of the graphite. Spallation was observed not only on the backside of the target, but also on its front (irradiated) surface. The morphology of the front and rear surfaces of the targets was studied using the optical and scanning electron microscopy. The structure of the graphite in irradiated area on the facial side as well as in the spallation zone on the rear side of the target was investigated by Raman scattering method. A comparison of the dynamic strength of the graphite with the dynamic strength of a synthetic diamond is done.

Strength of synthetic diamonds under tensile stresses produced by picosecond laser action

Results of an experimental-theoretical study of spallation in synthetic diamonds are presented. In this study, data were first obtained on dynamic tensile strength of poly- and singlecrystal diamond samples at mechanical loads of up to 0.34 TPa and strain rates of 10–100 µs−1. Shock-wave loading was performed by 70 ps laser pulses on a Kamerton-T facility using a Nd:glass laser (second harmonics λ = 527 nm, pulse energy of up to ≈3 J) at intensities of ≈8 TW/cm2. The obtained maximal value of the spall strength ≈16.4 GPa is 24% of the theoretical ultimate strength of diamond. Raman scattering experiments showed that a small amount of diamond was graphitized in the spall area on the backside of the sample.

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.