Ultrafast Imaging Of Femtosecond Laser-induced Periodic Ripples On The Surface Of Silver Film

The formation of laser-induced periodic surface structure (LIPSS) on metal、 semiconductors and dielectrics has gained remarkable attraction because of its extensive applications. Such as observation, enhanced luminescence, colorizing metal, self-cleaning on the surface, raman enhancement, etc. The period of LIPSS is always smaller than λ. The formation mechanism of LIPSS is very important, strongly dependent of the characteristics of the materials and the incident electromagnetic field, but it is still a challenging problem. This paper reports the dynamics of femtosecond laser-induced periodic ripples on silver film by a time-resolved pump-probe imaging method. After 1-6 pump pulses irradiation, temporal evolution of the periodic ripples on sample surface is observed. The premier ripples appear in the initial 50-70 ps after the second fs laser irradiation, and the ripple positions keep unmoved until the formation processes is completed in 1000 ps. The results suggest that the periodic deposition of laser energy during the interaction between femtosecond laser pulses and sample surface plays a dominant role in the formation of periodic ripples, which is caused by the excitation of surface plasmon polariton. During the solidification process, some ripples become shallow and even disappear because of surface melting.