  Costache et al. have reported recently a new type of periodic patterns
generated at femtosecond laser ablation of transparent dielectrics (Appl. Surf.
Sci. 186, 352(2002)). They show features known from other pattern forming
systems far from equilibrium, like point and line defects or grain boundaries,
and cannot be explained by the classical theory. The present work is an attempt
to investigate these pattern by means of a generalized Kuramoto-Shivashinsky
equation derived from the Bradley et al. and Cuerno et al. model for ripple
formation at ion beam sputtering of surfaces.
