Adjustment of surface morphologies of subwavelength-rippled structures on titanium using femtosecond lasers: The role of incubation

Laser-induced periodic surface structures have been extensively studied for various materials because of their promising applications. For these applications, uniform rippled structures with well-defined large areas are required. However, the efficient fabrication of uniform rippled structures is a challenge. Morphologies of rippled structures of multiple-shot-ablated regions considerably affect the processing efficiency of uniform rippled structures because incubation effects are crucial. In this study, the effects of a pulse number and irradiation modes on surface morphologies of rippled structures on the titanium surface are experimentally studied. The experimental results indicate the following: (1) Samples first irradiated using several shots and then using remaining shots by designing laser pulse irradiation modes exhibit improved surface morphologies, such as larger ablation areas and finer rippled structures. (2) When the pulse number in the first series is less than that in the second series, the rippled structures are characterized using larger areas and periods. (3) The ablated areas with rippled structures increase with the increasing number of pulses. (4) The periods of ripples reduce with the increasing number of pulses. Therefore, according to different requirements, uniform rippled structures can be efficiently fabricated and adjusted using the designed laser pulse modes and pulse number.