Microscopic energy transport through photon-electron- phonon interactions during ultrashort laser ablation of wide bandgap materials Part II: Phase change

Energy transport in femtosecond laser ablation can be divided into two stages: 1) laser energy absorption by electrons during the pulse irradiation, and 2) phase change stage that absorbed energy redistributes in bulk materials leading to material removals. We review challenges in understanding the phase change process mainly for the femtosecond ablation of wide bandgap materials at the intensities on the order of 10¹³-10¹⁴ W/cm². Thermal vaporization and Coulomb explosion are two major mechanisms considered for material removals. Based on the discussions of energy transport, the estimation equations and unsolved problems for threshold fluence and ablation depth are presented.