Time-resolved ultrasonic studies revealed a second, delayed ablative pressure pulse after the first primary sub-critical ablative plasma pressure pulse in a silicon wafer irradiated by a 266-nm, 10-ns laser. The intensity-dependent delay time for the second pulse indicates the existence of a corresponding intensity-dependent homogeneous vapor bubble nucleation time in the superheated molten silicon prior its phase explosion and ablative removal, since the

integral pressure correlates with the ablation rate. The transient hot ablative plasma with calculated peak temperature ∼ 30-90 eV and pressure ∼ 20-110 GPa is suggested to superheat the bulk silicon via short-wavelength recombination and Bremsstrahlung emission.