Periodic surface structures induced by femtosecond laser single pulse and pulse trains on metals

We experimentally investigate the formation of nanostructures on the surfaces of aluminum and copper with femtosecond laser single pulse and pulse trains. Subwavelength ripples were obtained on the surface of aluminum. The ripples' period gradually increases as the laser pulse fluence increases. With a single pulse ablation of copper, interlaced ripple structures formed on the wall of the crater when the laser pulse number is 2000, the reason for interlaced ripple formation is also discussed. A large scale of ripple structures formed by using a femtosecond laser single pulse and pulse trains to scan copper. We suggest that a pulse train is more effective in obtaining high quality ripple structures compared with a femtosecond laser single pulse.