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 10(9) s(-1) and a spall thickness of 250-300 nm is larger than half the ultimate strength of aluminum.