Fig. 1. Measurement of filament-induced acoustic wave and fluorescence signal. (a) Schematic of experimental facility; (b) acoustic time-domain signal; (c) N₂ fluorescence spectrum with 337 nm fluorescence time-domain signal detected by PMT shown in inset

Fig. 2. Measurement results by acoustic and fluorescent methods. (a) Acoustic signal intensity induced by point source (inset: image of point source) and (b) 337 nm N₂ fluorescence signal intensity versus propagation distance when f =50 mm; (c) acoustic signal intensity and (d) 337 nm N₂ fluorescence signal intensity versus propagation distance when f =10 m and single pulse energy is 4.9 mJ

Fig. 3. Effects of pulse energy on spatial distribution of filament. Spatial distributions of (a) acoustic signal intensity and (b) 337 nm N₂ fluorescence spectral intensity induced by filaments under different pulse energies

Fig. 4. Measurement results by acoustic and fluorescent characterization methods. (a) Starting position and (b) length of filament versus laser energy

Fig. 5. Differences in measurement results of acoustic and fluorescence methods. (a) Normalized evolution curves of acoustic signal intensity and 337 nm N₂ fluorescence signal intensity with laser transmission distance; (b) relative deviation between acoustic signal and fluorescent signal