Formation of periodic nanostructures on aluminum surface by femtosecond laser pulses

One-dimensional periodic nanostructures have been produced on the surface of an aluminum specimen using femtosecond laser pulses at wavelengths of 744 and 248 nm. The nanostructurization of the specimen has been conducted in water and in air in the preablation regime. We investigate the dependence that the surface topology has on the parameters of laser radiation (wavelength, fluence, and number of pulses), as well as on the medium in contact with the specimen surface. A calculation of the optical characteristics of aluminum as they depend on the electron temperature is performed that is good at describing the dependence that the reflection of the p-polarized infrared femtosecond pulses of pumping has on the fluence. Using these optical characteristics of the photoexcited aluminum within the interferential model, periods of the aluminum surface nanogratings are estimated which are in good agreement with the periods measured experimentally.