Simple formula for the interspaces of periodic grating structures self-organized on metal surfaces by femtosecond laser ablation

Self-organized grating structures formed on Mo and Ti metal surfaces irradiated with femtosecond laser pulses at wavelengths of 800 and 400 nm are investigated by electron microscopy. We observe the formation of the self-organized grating structures on the metals irradiated with 400-nm laser pulses at low laser fluence in narrow fluence ranges. The interspaces of the grating structure depend on the wavelength and fluence of the laser. We find that the dependence of the grating interspaces on laser fluence can be explained by a simple formula for induction of a surface-plasma wave through the parametric decay of laser light.