Fig. 2

a The schematic illustration and profile SEM image of micro-lines fabricated by varying the laser focus at different relative positions (without the sacrificial layer, after HF etching). b The relationship of the depth/width of the resultant micro-lines and the relative position of laser focus to the sapphire surface. c The dependence of the depth of undamaged regions on the laser fluence. The insets are intensity distribution of laser focus with low (left) and high (right) fluence. d The schematic illustration and profile SEM image of micro-lines fabricated by varying the laser focus at different relative positions in the presence of a sacrificial layer (after HF etching).