Fig. 1. (a) Schematic diagram of parallel fabrication process of MLAs. (b) Optical setup of multi-beam femtosecond laser irradiation showed in dashed box in (a).

Fig. 2. Typical etched surface morphologies of laser-cut silicon in mixed acid (a) HF∶HNO3=10∶1 and (b) HF∶HNO3=1∶6 after 2 min.

Fig. 3. Typical etched surface morphologies of laser-ablated microholes in mixed acid (a) HF∶HNO3∶HAC=3∶12∶10 and (b) HF∶HNO3∶H2SO4∶HAC=3∶12∶1∶10 after 40 min.

Fig. 4. (a)–(c) are MLAs fabricated at a laser pulse number of 100 and different powers (for a single microhole, the same below) of (a) 2, (b) 10, and (c) 15 mW. The etching time for (a)–(c) was 30 min. (d)–(f) are MLAs fabricated at 5 mW with different pulse numbers of (d) 100, (e) 300, and (f) 500. The etching time for (d)–(f) was 60 min. Figure 4 was captured by the optical microscopy.

Fig. 5. (a) SEM image of MLA fabricated at a laser power of 5 mW, a pulse number of 500, and an etching time of 60 min. The fill factor of the MLA is about 92.8%. (b) The 3D observation of the marked part in (a). (c) The cross-section profile of microlenses along the direction marked in (b).

Fig. 6. Image array formed by MLA showed in Fig. 5. The inset shows the object “TEC.”