Fig. 1. Schematic of experimental setup for processing high-aspect-ratio straight and inverted tapered holes using spinning beam method

Fig. 2. Schematics of spinning beam drilling method. (a) After passing through tilted optical window, lateral displacement is generated for femtosecond laser, and optical window and half-wave plate rotate at angular speed of ω; (b) rotation of femtosecond laser after being focused by lens is similar to precession of gyroscope, with angular velocity of ω around Z-axis, and polarization direction rotates at angular velocity of 2ω around direction of light propagation

Fig. 3. Holes processed using spinning beam machining method. (a) Variation of hole diameters on top and bottom surfaces with processing time; (b) variation of hole taper angle with processing time; (c1)‒(c8) SEM images of top and bottom surfaces of holes at different processing time

Fig. 4. Holes processed using polarization trepanning method (first stage of two-stage drilling). (a) Change in hole diameter on bottom surface with processing time; (b) change in hole taper angle with processing time; (c1)‒(c4) SEM images of top and bottom surfaces of holes at different processing time

Fig. 5. Holes processed using polarization trepanning method (second stage of two-stage drilling). (a) Change in hole diameter on bottom surface with processing time; (b) change in hole taper angle with processing time; (c1)‒(c6) SEM images of top and bottom surfaces of holes at different processing time

Fig. 6. Comparison between spinning beam machining method and dual-stage machining method

Fig. 7. SEM images of holes before and after adding circular mask. (a)‒(d) Polarization trepanning machining for 1500 s;