SEM images of the titanium alloy surface formed under picosecond laser treatment. (a) p = 25 W, V = 500 mm/s, n = 5, f = 400 kHz, (b) p = 25 W, V = 1000 mm/s, n = 10, f = 100 kHz, (c) p = 30 W, V = 2000 mm/s, n = 10, f = 400 kHz, and (d) p = 20 W, V = 2000 mm/s, n = 10, f = 400 kHz47