Laser ablation of thin films with very high induced stresses

The ablation of chromium films by nanosecond laser pulses was tracked by triple-frame high-speed transmission electron microscopy and selected area diffraction (exposure time approximate to7-11 ns, frame spacings 20 ns-10 mus). At lower fluences the films were shattered during heatup and cooldown, producing debris with huge in-plane accelerations up to 10(10) m/s(2) and rotations with 10(6) rps. At higher fluences the ablation is proceeded by a domain-patterned evaporation. These effects are responsible for the high damage in laser-produced patterns in chromium films. They were all explained as being due to stress waves, launched by an extremely fast nonthermal 3%-4% expansion/contraction of the bcc lattice constant during heating/cooling. (C) 2002 American Institute of Physics.