High-spatial Frequency Periodic Structures Induced On Metals Surface By Femtosecond Laser

Laser induced periodic surface structures(LIPSSs)have been studied extensively for a long time,which can be used for some specific applications(such as manufacture of grating,color marking of metallic surfaces and bio-mimetic surfaces).Especially with the advent of fs-laser,not only low-spatial frequency LIPSSs(LSFLs:0.5<Λ/λ)with period close to the incident laser wavelength are obtained,but also high-spatial frequency LIPSSs(HSFLs:Λ/λ<0.5)with period much smaller than the laser wavelength are formed.On one hand,although several mechanisms have been put forward to interpret the HSFLs formation,the formation of HSFLs is still debated.On the other hand,it is unclear why the formation of HSFLs on metals is harder than dielectrics and semiconductors.Therefore the study of HSFLs formation on the metal surfaces has a great significance.In this paper,we report the formation of LIPSSs on Fe film,Fe,Ti,Ni,Cu and A1 surfaces under fs-laser(λ=800 nm)irradiation.LSFLs emerge on all metal surfaces,but HSFLs just form on the Fe and Ti surface.HSFLs with period of 150-230 nm form on Fe film surface,while on the bulk Fe surface,HSFLs with period of 230 nm are obtained.On the Ti surface,not only HSFLs(220-340 nm)perpendicular to the laser polarization,but also HSFLs(100±10 nm)parallel to the laser polarization are obtained.Combining surface plasmon polaritons with second harmonics generation and Sipe model,we find that surface plasmon polaritons,which emerge at the interface between the metal and oxide layer,maybe play a vital role in the LIPSSs formation.Analyzing the thermal diffusivity and reflectivity,we find that the smaller the thermal diffusivity and reflectivity,the easier the HSFLs formation.The preparation of the HSFLs on different metals,not only helps us understand the LIPSSs formation mechanism for different materials(dielectric,semiconductor,metal),but also provides a good way to manufacture functional devices.