Fig. 1. Direct measurement of the light intensity inside the filament for Gaussian beam (a), circular iris (b) and stellate iris (c) modulation by the method of metal foil hole burning^[37]

Fig. 2. Evolution of plasma density under different focusing conditions^[47]

Fig. 3. Diffraction modulation pattern of 1 kHz repetition rate filament on probe light. (a) The modulation of the low-density region on probe light; (b)―(f) diffraction modulation pattern of plasma at different delay times^[48]

Fig. 4. Plasma evolution results obtained by probe-pump detection experiments with and without low-density refractive index correction. (a) Temporal evolutions of peak electron density; (b) temporal evolutions of filament diameter; (c) transverse distribution of electron density at different delay times^[48]

Fig. 5. Dependence of the plasma density on the laser pulse energy^[49]

Fig. 6. The peak position (bimodal fitting) of the fluorescence signal as a function of the pulse energy at repetition rates of 1 kHz (a), 500 Hz (b), 100 Hz (c), 50 Hz (d). The point of intersection between the red fitted lines indicates the critical power for self-focusing. (e) The critical power as a function of the repetition rate obtained by using Gaussian fitting and the bimodal fitting^[60]

Fig. 7. Intensity distribution determined by the ratio of the fluorescence signals of nitrogen 337 nm and 391 nm at different pulse energies 0.1 mJ (a), 0.2 mJ (b), 0.7 mJ (c), 1.2 mJ (d)^[63]

Fig. 8. The simulation results of intensity distribution inside the filament with different pulse energies of 0.1 mJ (a), 0.2 mJ (b), 0.7 mJ (c), 1.2 mJ (d)^[63]

Fig. 9. The spatial distribution of plasma density under different repetition rates^[67]

Fig. 10. The Boltzmann plots for O I from 100 Hz and 1000 Hz filaments (a) and the plasma temperature as a function of the laser repetition rate (b)^[67]

Fig. 11. Experiment results of spectral intensity distribution at different repetition rates^[69]

Fig. 12. Pointing stability of the forward SC laser and filament as a function of the applied high voltage at different repetition rates^[70]

Fig. 13. Atmospheric sensing of filament induced supercontinuum lidar. (a) Schematic of filament induced supercontinuum lidar; (b) the relationship between lidar signal and vertical distance at different wavelengths; (c) high resolution atmospheric absorption spectra at the vertical distance of 4.5 km^[75]

Fig. 14. Schematic of spaceborne filament for atmospheric remote sensing^[84]