Thermocavitation melt instability and micro-crown formation near the threshold for femtosecond laser spallation of a silicon surface

Thermocavitation instability of a molten layer on a silicon surface was experimentally revealed in the form of a microscale surface crown-like feature produced by multiple infrared or visible femtosecond laser pulses near the spallation threshold fluence. The number of crown spikes varied versus the crown perimeter, monotonically increasing with increasing laser shot number. The instability dynamics was described in terms of the intermediate crown structures (the spike number) using the proposed thermocavitation model based on the Kuramoto-Sivashinsky hydrodynamic equation.