The Formation And Ultrafast Dynamics Of Subwavelength And Deep-subwavelength Periodic Nanoripples On Stainless Steel Irradiated By Femtosecond Laser Pulses

Laser induced periodic ripples on solid material is an important direction that has been studied. The period of ripple induced by long-pulse laser is usually closed to the wavelength of the incident laser. Since femtosecond laser appeared, the periodic ripples on the metal induced with the femtosecond laser are subwavelength ripples (0.4<Λ/λ<1). In the recent, the deep subwavelength periodic ripples are induced on metal with femtosecond laser. But the mechanism and the condition of the formation of the deep subwavelength periodic ripples need further research. In this paper, we report the formation of subwavelength periodic ripples (0.4λ<Λ<λ) and deep subwavelength periodic ripples (Λ≤0.4λ) on stainless steel irradiated by 800 nm femtosecond laser pulses. The split of subwavelength periodic ripples (periodΛ≥400 nm) plays the decisive role in the formation of deep subwavelength periodic ripples (Λ≤320 nm). We further conduct pump-probe experiments and numerical simulations to study the ultrafast dynamics of the formation of surface periodic ripples.