Crystalline orientation effects on material removal of sapphire by femtosecond laser irradiation

C-, M −, A- and R-plane sapphire plates have been irradiated by a femtosecond laser with different laser parameters. The influences of crystal orientations on irradiation damage of single- and multiple-pulse have been investigated. The experimental results illustrate that the damage morphology, damage threshold, material removal rate and accumulation of laser damage depend on the crystal orientation. This dependence is related to the different bonding energies between adjacent atomic layers for different crystal orientations. The theoretical analysis indicates that bonding energy between adjacent atomic layers of C-, M −, A- and R-plane sapphire plates increases in the order of C-plane < M-plane < A-plane < R-plane. The experimental damage threshold of different crystal planes increases in the order of C-plane < M-plane < A-plane < R-plane and material removal rate decreases in the order of C-plane > M-plane > A-plane > R-plane. The analytical result is in agreement with the experimental result. The experiment results also present that the damage accumulation of M-plane sapphire plates is the largest. Therefore, M-plane is more easily to form cracks under multiple pulse irradiation.