AgI is an important man-made ice nucleus for the catalyzing of cold clouds in weather modification. Its condensation efficiency has always been in the focus of attention. In order to increase the nucleation effectiveness of the AgI pyrotechnic in the cloud, hygroscopic salts need to be mixed.
Femtosecond laser filament is a new technique developed in recent years to induce water condensation. When the AgI pyrotechnic is combined with the irradiation of a femtosecond laser filament, the water condensation yield is expected to increase, considering that laser filaments can provide both the highly hygroscopic acid and the strong airflow for AgI nucleants.
Recently, researchers led by Professor LIU Jiansheng at Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences and Chinese Academy of Meteorological Science, have combined AgI pyrotechnic with the irradiation of a femtosecond laser filament. The side Mie scattering of particles, snow formation, laser-induced side fluorescence spectra, and particle number and size were demonstrated for the cases with and without the assistance of laser filaments.
In their experiments, regenerative 800-nm Ti: sapphire laser pulses of 29 fs/6.7 mJ/1 kHz were used. The laser pulses were focused by an f = 400 mm lens, and then propagated collinearly with the 532-nm probe laser into a cloud chamber [0.5 m (length) × 0.5 m (width) × 0.2 m (height)]. AgI pyrotechnic was burned in a closed cubic chamber of 1 m3, and 25-ml or 50-ml nucleants were injected into the cloud chamber using an injection syringe.
It is found that when the AgI nucleants were irradiated by laser filaments, the condensate particles on the glass slide become highly soluble, and their sizes become slightly larger. The amount of snow on the cold bottom plate increases by 4.2–13.1%. The concentration of NO3- in the melt water increases by more than ten times.
This research indicates that laser filaments have a potential to be suitable as an alternative method to mix hygroscopic compounds (HNO3) into AgI pyrotechnics and increase the efficiency of water condensation.
The research entitled “Femtosecond laser filament-assisted AgI-type pyrotechnic nucleant-induced water condensation in a cloud chamber” has been published in Opt. Express.
This work was supported by the National Natural Science Foundation of China and the State Key Laboratory Program of the Chinese Ministry of Science and Technology.
Microscope images of particles condensed on the glass slide
Mr. Cao Yong
General Administrative Office
Shanghai Institute of Optics and Fine Mechanics, CAS