Dynamics of plume and crater formation after action of femtosecond laser pulse

Using microinterferometric method, a transition in laser plume from the regime with spallation to the regime without spallation is experimentally studied for the first time. The transition occurs when the fluence Finc of incident radiation exceeds a threshold of ‘‘evaporation’’ ðFincÞev. It has been shown previously that the spallation layer is formed at fluence above the ablation threshold ðFincÞabl. Thus the spallation exists within the limits ðFincÞabl Fev