Two-dimensional periodic structure induced by single-beam femtosecond laser pulses irradiating titanium.

A novel two-dimensional (2-D) periodic structure on the ablated hole wall is formed by using the method of single-beam femtosecond laser pulses irradiating a titanium target. This 2-D structure on the ablated surface, after consecutive irradiation of 10000 pulses, presents different spatial periods which characters a 1500 nm period along the hole wall in the vertical direction and a 400 nm period in the azimuthal direction of the hole. The reported experimental results can be well interpreted by a prophetic theoretical model of Bonch-Bruevich (A. M. Bonch-Bruevich et al., Opt. Eng. 31, 718 (1992)).