Specific features of the behaviour of targets under negative pressures created by a picosecond laser pulse

New experimental data are obtained concerning the character of spallation and the mechanical strength of targets made of aluminium, aluminium-magnesium alloy (AMg6M), polymethylmethacrylate (PMMA, plexiglass), tantalum, copper, tungsten, palladium, silicon, and lead under the impact of laser radiation with the duration 70 ps. The specific features of the spallation phenomenon, in which the separation of a part of the target substance occurs at the back surface as a result of the effect of negative pressures (tensile stresses) in the substance, are experimentally studied. To determine the time moment of spallation, the electrocontact method of measuring the velocity of the spalled layer is developed and implemented. The obtained results show that the values of spall strength of the studied materials at moderate amplitudes of the shock-wave effect agree with the known literature data, while at higher pressures the growth of spall strength is observed, which is an evidence of the material hardening. The results of the studies demonstrate that the dynamic strength of a substance depends on both the duration and the amplitude of the shock-wave impact on the target.