Pyrolysis-induced fragmentation and blowoff of laser-irradiated surfaces

During pyrolysis of a laser-irradiated material, large pressures must develop within the internal porous structure in order to transport the volatile gases to the free surface. These high internal pressures may cause macroscopic fracture and/or solid-phase mass removal prior to complete pyrolysis or vaporization. A pyrolysis/volatile transport model is used to assess the conditions under which this enhanced mass removal mechanism will occur. Critical energy densities (approximately kJ/g) are predicted to be relatively insensitive to the physical parameters involved. The threshold pulse fluence (J/sq cm absorbed by the target) is sensitive to the laser pulse duration, the pyrolysis rate, and the laser absorption depth.