Fig. 1. Schematic of frost assisted femtosecond laser processing station

Fig. 2. Schematic of TEC temperature control system

Fig. 3. Frost layer thickness versus time under different relative humidity values

Fig. 4. Surface morphologies of laser ablated microgrooves assisted by frost layer under different laser powers. Surface morphologies when laser powers are (a) 0.3, (b) 0.5, (c) 0.6 W, respectively; (d)‒(f) corresponding 3D morphologies of microgrooves

Fig. 5. Surface morphologies of laser ablated microgrooves assisted by frost layers with different thicknesses when scanning speed is 0.4 mm/s. Surface morphologies when frost thicknesses are (a) 2, (b) 6, and (c) 10 μm, respectively; (d)‒(f) corresponding 3D morphologies of microgrooves

Fig. 6. Surface morphologies of laser ablated microgrooves assisted by frost layers with different thicknesses when scanning speed is 0.2 mm/s. Surface morphologies when frost thicknesses are (a) 2, (b) 6, and (c) 10 μm, respectively; (d)‒(f) corresponding 3D morphologies of microgrooves

Fig. 7. Surface morphologies of laser-ablated microgrooves assisted by frost with different repetition frequencies. Surface morphologies when repetition frequencies are (a) 200, (b) 500, (c) 800 kHz, respectively; (d)‒(f) corresponding 3D morphologies of microgrooves

Fig. 8. In-situ micrographs at different moments during surface etching process with laser assisted by frost. (a) 0.5 s; (b) 1.5 s; (c) 2.5 s; (d) 3.5 s

Fig. 9. SEM images with frost assisted processing and frost-free processing. (a) Frost assisted processing, 500× magnification; (b) frost-free processing, 500× magnification; (c) frost assisted processing, 10000× magnification; (d) frost-free processing, 10000× magnification