Interaction of Laser Radiation with Transparent Material Porous Targets

The paper reports on a number of new physical phenomena found in the study of the laser radiation impact on porous materials. This applies to formation of laser plume at intensities significantly below the damage threshold of single crystal material which leads to the formation of needle-like structure with a diameter of similar to 1mm and a height of 8 mm on the target surface. The plume formation is characterized by irregular glow and spallation of the front surface of the target. In our opinion, these phenomena are caused by the transition from vapor to vapor-drop ablation, which leads to 6-8 times increase of the laser crater depth at the same energy of the laser pulse. At the same time, the vapor-drop mode of ablation is typical mainly for transparent materials, and the vapor mode is typical for materials that are opaque for laser radiation. Mathematical models explaining the reasons for the above processes and facts are presented.