Fig. 1. Plasma columns and their corresponding grey values generated by (a) positively and (b) negatively chirped sub-picosecond laser pulses with a pulse duration of (a) ∼0.92  ps and (b) 0.97 ps at a laser power of 6.5 W, respectively. The images of the plasma columns were captured by a camera (Nikon D7000: shutter speed S=1/40  s, f number F=5, light sensitivity ISO=1600).

Fig. 2. Airflow generated by (a) positively and (b) negatively chirped sub-picosecond laser pulses with a pulse duration of (a) ∼0.92  ps and (b) 0.97 ps at a laser power of 6.5 W, respectively. The images were captured by a Nikon D7000 camera (S=1/50  s, F=3.2, ISO=1600).

Fig. 3. (a) Snow on the cold plate without laser shooting. (b) Close-up view of part of the snow in (a). The shooting conditions of the camera are S=1/40  s, F=3.2, and ISO=1600 for (a), S=1/40  s, F=5.0, and ISO=1600 for (b).

Fig. 4. Snow piles on the cold plate with (a), (b) positively and (c), (d) negatively chirped sub-picosecond laser pulses at a laser power of 6.5 W with a pulse duration of (a), (b) ∼0.92  ps and (c), (d) 0.97 ps, respectively; (b) and (d) are close-up views of (a) and (c). Panels (a), (c) and (b), (d) are in the same scale. The shooting conditions of the camera are S=1/50  s, F=3.2, and ISO=1600 for (a), S=1/50  s, F=5.0, and ISO=1600 for (b), and S=1/40  s, F=5.0, and ISO=1600 for (c) and (d).

Fig. 5. Dependence of the amount of small snow piles below the plasma columns (black circles and red squares, left scale) and concentration of NO3− in the melted water (green triangles and blue stars, right scale) in the pulse duration of positively (black circles and green triangles) and negatively chirped pulses (red squares and blue stars), respectively. There is no chirp for the 27 fs pulse duration. The pulse duration was measured at the laser exit.