Fig. 1. Schematic of femtosecond laser filamentation process^[2]. (a) Self-focusing effect; (b) self-defocusing effect; (c) dynamic balance process inside filament

Fig. 2. Acid-base property of femtosecond laser induced snow formation measured by using pH test papers^[22]. (a) Snow pile (indicated by white dotted circle) induced by femtosecond laser filamentation; (b) acidity-base property of snow/ice covered on cold plate at different positions measured by using pH test papers; (c) pH standard colorimetric card

Fig. 3. Number density [dN/d(lnD_p)] of 10 Hz femtosecond filamentation induced aerosols under different atmospheric conditions. (a) Humid argon (Ar), humid argon (Ar)+oxygen (O₂), etc.; (b) humid air, humid air+NH₃, humid air+(NH₄)₂SO₄, etc.^[28]

Fig. 4. Formation of particles and trace gases induced by 1 kHz laser filamentation^[30]. (a) N_a and m_a versus time; (b) particle number size distribution (PNSD) versus time; (c) particle mass size distribution (PMSD) versus time; (d) temporal evolution of mass mixing ratios between trace gases and ambient air

Fig. 5. Component analysis of 10 Hz femtosecond filamentation induced aerosol formation^[24]. (a) Mass increase of different size aerosols; (b) mass distribution of different components inside aerosols

Fig. 6. Relationship among number density of femtosecond filamentation induced nanoparticle aerosols, filament number, and photon bath contribution^[31]. (a) Laser-induced nanoparticle number density, filament number and photon bath contribution versus laser intensity; (b) laser-induced number density and filament number versus laser intensity or pulse duration

Fig. 7. Temporal evolution of femtosecond filamentation induced secondary ice crystal formation. (a) t=-12 μs; (b) t=0 μs; (c) t=12 μs; (d) t=12.1 ms; (e) t=19.1 ms; (f) t=20.1 ms^[33]

Fig. 8. Increase of optical density and ice crystal density of cirrus cloud irradiated by femtosecond laser pulses. (a) With (solid lines) and without (dashed lines) femtosecond filament action, gas phase temperature (T) and pressure (P) versus time; (b) with (solid lines) and without (dashed lines) femtosecond filament action, relative humidity with respect to ice phase (H_ri) and duration of laser operation (J) ve

Fig. 9. Femtosecond filamentation induced airflow thermodynamic motion under different repetition rates ^[35].(a)(d) 1 Hz; (b)(e) 15 Hz; (c)(f) 1 kHz

Fig. 10. Femtosecond filamentation induced airflow thermodynamic motion under different ambient air conditions^[38]. (a) Humid air; (b) humid helium

Fig. 11. Scattering images of 1.55 μm telecom laser propagating in air. (a)(c) Side view; (b)(d) front view; (e) transmission powers of 1.55 μm telecom laser through femtosecond filaments at different repetition rates ^[39]

Fig. 12. Femtosecond laser induced water condensation. (a) Side scattering image of scene inside chamber without laser filament; (b) side scattering image of scene inside chamber with laser filament; (c) 2D image of different size droplet density versus laser irradation duration; (d) line image of different size droplet density versus laser irradiation duration; (e) sketch of femtosecond laser interacting with ambient atmosphere; (f) relative increase rate of Mie backscattering signals^[

Fig. 13. Femtosecond laser induced snow formation. (a) Schematic of experimental setup; (b) fluorescence of laser filament in cloud chamber without probe beam (top), and Mie scattering patterns around filament induced by probe beam (bottom); (c) close-up shot for snowpack in Fig. 13(b); (d) laser induced snow formation on whole bottom base plate after firing 1 kHz laser pulse for 2 h; (e) close-up shot for snowpack in Fig. 13(d)<

Fig. 14. Physical picture of femtosecond laser-based atmosphere modulation