Material removal on silicon towards atomic and close-to-atomic scale by infrared femtosecond laser

Ultrashort laser pulse is a widely used tool for high precision machining. However, the understanding on its minimum removal is still unclear. In this paper, single laser pulse (232 fs at 1030 nm) is used to study material removal of silicon from its (001) surface at near threshold fluence. The damage threshold, effective attenuation length, removal depth and ablation morphology are investigated systematically using atomic force microscopy. The minimum material removal of down to 1 nm is observed experimentally. A novel molecular dynamics method coupled with two temperature model is developed to reveal multiphoton ionization and explore the dynamic process. Results show that laser-induced plasma plays important role in the interaction process. The ablation crater is generated by plasma ejection and the outer rim around the crater is formed by the recoil pressure due to high pressure plasma expanding.