Characterization of the ablation morphology induced by the first pulse with a fluence of 7.27 J/cm2. (a) SEM image of the surface structure of silicon. (b) Atomic force microscope (AFM) profile of the cross-section of the structure in (a). (c) Sketch of the optical system for characterizing light focusing ability of the silicon-based crater array. (d) Focal spots image obtained with a CCD on the focal plane of the crater. (e) Calculated electric field distribution of the reflected pulse (N = 1) from untreated plane silicon surface. (f) Calculated electric field distribution of the reflected pulse (N = 2) from the crater generated by the first pulse. The focal spot of the incident pulse in (e) and (f) was set to be on the sample surface, indicated by right edge of the images.