Phase explosion in laser-pulsed metal films

Nickel, chromium, and germanium films were treated by nanosecond 7–30 J cm−2 laser pulses. The evaporation, comprising surface evaporation, normal boiling, and homogeneous nucleation of gas bubbles in the liquid metals were visualized by a high-speed transmission electron microscope on the nanosecond time scale. Contrary to phase explosion, the first two mechanisms are marginal at these fluences. Nucleation rates of gas bubbles were determined by imaging. Plasma temperatures were estimated from transient small angle scattering. The results can be used to check high-temperature material parameters.