Nonlinear waves generated on liquid silicon layer by femtosecond laser pulses

Two-dimensional nonlinear waves are generated by multipulse femtosecond ultraviolet laser irradiation of silicon above the ablation threshold. The train of 120-190 pulses generates the unidirectional cnoidal-like waves as well as the Y- and X-type configurations. In the region of high laser intensity, the interaction of line solitary-like waves give rise to the complex network structure. For 200 ≤ N < 220, the transition from stable into unstable waves takes place. At the critical number of pulses (≥230), the catastrophic destruction of cnoidal-like and solitary-like waves, takes place. Thus, the number of pulses plays the role of the control parameter. The stable cnoidal-like and solitary-like waves in a thin layer of molten silicon are reproduced by using the Kadomtsev-Petviashvili equation with negative dispersion (KP-II), and the unstable ones by using the KP-I equation with positive dispersion.