Fig. 1. Schematic diagram of experimental setup for measurement of number of filaments of femtosecond vortex beams in fused silica

Fig. 2. Typical filament distributions generated in fused silica by vortex beams with m=1 and m=2, focused by lenses with different focal lengths. (a)(d) 500 mm; (b)(e) 400 mm; (c)(f) 300 mm

Fig. 3. Relationship between filament number and input energy under different vortex beams with different topological charges and focusing conditions. (a) Experimental measurement results; (b) theoretical equation calculation results

Fig. 4. Variation of blue-side cut-off wavelength of laser spectrum with input energy under different focusing conditions. (a) Focal length f=300 mm; (b) focal length f=400 mm; (c) focal length f=500 mm

Fig. 5. Number of filaments generated in fused silica by vortex beams with topological charges of 1 and 2 focused by different lenses as a function of P/Pcr0,f and P/Pcrm,f. (a) P/Pcr0,f; (b) P/Pcrm,f