Fig. 1

(a) Optical field distribution of a Gauss laser beam and the schematic program of inside-out femtosecond laser scanning technology. (b) The dependence of the depth of the undamaged region (d_z) on the laser fluence (A_0^2). The inset is the SEM image of a typical undamaged region. (c) The schematic illustration of laser modification and subsequent wet etching of sapphire surface without and with a sacrificial layer.