Surface damage induced by a combined millisecond and nanosecond laser

The surface damage morphologies of single-crystal silicon induced by a combined pulse laser (CPL) and a single millisecond laser are investigated, respectively. The CPL includes a millisecond (ms) laser superposed by a nanosecond (ns) laser. Inspected by an optical microscope, it was found that the surface damage was more serious when the sample was irradiated by the CPL than by a single ms laser with the same incident laser energy. Besides surface cleavage, obvious ablation and fold areas were discovered by CPL irradiation. A two-dimensional spatial axisymmetric model was established to assess the difference between single ms laser and CPL irradiation and explain the generation mechanism of the different surface damage. This was attributed to the preheating effect by the ms laser and the surface damage caused by the ns laser.