Fig. 1. Schematic diagram of the femtosecond Bessel beams irradiation. Beam propagation direction is along z-axis. HWP, half-wave plate; Zmax, focal depth of the initial Bessel beams.

Fig. 2. (a) Cross-sectional optical image of laser-modified regions formed in fused silica by femtosecond Bessel beams irradiation at E=40  μJ, v=5  μm/s with their magnifications; (b) Beam propagation direction is along z-axis.

Fig. 3. (a) Cross sectional SEM images of the microgroove after HF etching at HF solutions with concentration of 10% in ultrasonic cleaner for 2 h; (b) magnification of the entrance of the groove; (c) magnification of the medium part of the groove; (d) magnification of the bottom part of the groove.

Fig. 4. Dependence curve of aspect ratio on the pulse energy and the scanning velocity is 5 μm/s, when the femtosecond Bessel beams were focused on the surface of the silica.