Fig. 1. Schematic of the setup (top view)

Fig. 2. Electric field intensity distribution on horizontal cutting plane of cone electrode

Fig. 3. Distribution of electric field intensity of laser filaments. (a) Overall view; (b) the zoom-in region of red dotted line section in Fig.3 (a)

Fig. 4. Distribution of electric field intensity and maximum electric field intensity under different filament lengths. (a) Distribution of electric field intensity; (b) maximum electric field intensity

Fig. 5. Real-color images. (a) Fluorescence image of interaction between laser filaments (6.22 mJ) and different voltages negative coronas; (b) negative coronas from the electrode under different voltages

Fig. 6. Fluorescence intensity distribution from the image at -60 kV. The tip position of the electrode is defined as 0, and the red dashed line indicates the reference line based on 3σ method which is used to define negative corona size. (a) Along laser filament (6.22 mJ); (b) along axial direction of the electrode (The negative direction of the yellow dashed line in the illustration is defined as the direction of the negative corona expansion)

Fig. 7. Negative corona size and filament length versus voltage. (a) Negative corona size; (b) filament length

Fig. 8. Real-color images of single laser filaments (0 kV) and interaction between laser filaments and negative coronas (-60 kV) under different laser energies. (a) 0 kV; (b) -60 kV

Fig. 9. Filament length and fluorescence intensity at the end of filament as functions of laser pulse energy

Fig. 10. Fluorescence intensity at the end of filament versus filament length

Fig. 11. Consumed corona power as a function of filament length during filament-induced negative corona discharge