Fig. 1. (a) Schematic diagram of tunable ultrafast laser Bessel beam processing system; (b) Geometric optical path diagram of tunable ultrafast laser Bessel beam processing system

Fig. 2. Light intensity of top view (top row) and side view (bottom row) of Bessel beams under different tuning modes.(a) Tunable mode Ⅰ; (b) Tunable mode Ⅱ; (c) Tunable mode Ⅲ

Fig. 3. Light intensity of Bessel beams under different tuning modes. (a) The intensity distribution along the cross section (X direction); (b) The intensity distribution along the laser beam propagation direction (Z direction)

Fig. 4. (a) Bessel beam detection experimental setup；(b), (e) The cross-sectional intensity distribution and intensity curve distribution of Bessel beam at a propagation distance of 290 mm under Tunable mode Ⅰ; (h), (k) At a propagation distance of 440 mm; (c), (f) The cross-sectional intensity distribution and intensity curve distribution of Bessel beam at a propagation distance of 170 mm under Tunable mode Ⅱ; (i), (l) At a propagation distance of 330 mm; (d), (g) The cross-sectional intensity distribution and intensity curve distribution of Bessel beam at a propagation distance of 30 mm under Tunable mode Ⅲ; (j), (m) At a propagation distance of 70 mm

Fig. 5. Comparison of the central main lobe radius of tunable Bessel beams under theoretical calculations, numerical simulations and experimental tests

Fig. 6. (a), (d) The micrographs of the front and back surfaces of the Bessel beam under Tunable mode Ⅰ; (b), (e) The micrographs of the front and back surfaces of the Bessel beam under Tunable mode Ⅱ; (c), (f) The micrographs of the front and back surfaces of the Bessel beam under Tunable mode Ⅲ

Table 1. The center main lobe radius and the maximum nondiffracting propagation distance of Bessel beam under different tuning modes