Laser ablation experiments are carried out using a high intensity laser (~1010 W/cm2) and basalt targets. Using a high-speed camera and a spectrometer, the radius and the temperature of the silicate vapor clouds generated by laser ablation are observed as a function of time. Then a numerical simulation of vapor expansion is carried out, and the thermodynamic state of the silicate vapor is determined so as to reproduce the experimental results. The result of the analysis indicates that the impact velocity which would generate a vapor cloud with this thermodynamic state is ~120 km/s for collisions between two basaltic bodies.