ИСТИНА

Using shadow photography technique we have observed shock acoustic wave from optical breakdown, excited in water by tightly focused Cr:Forsterite femtosecond laser beam, and have found two different regimes of shock wave generation by varying only the energy of laser pulse. At low energies a single spherical shock wave and cavitation bubble is generated from laser beam waist, and shock wave radius tends to saturation with energy increasing. At higher energies long laser filament in water is fired, that leads to the cylindrical shock wave generation and cavitation bubble in every nonlinear focus. The diameter of cavitation bubble depends on the distance from the first nonlinear focus. From shadow pictures we also estimated maximal velocity in the shock wave front of 3200±150m/s and pressure of 240±30 MPa.