Optics researchers from the University of Central Florida's College of Optics&Photonics and the University of Arizona are working on a new technique to aim a high-energy laser beam into clouds to make it rain or trigger lightning. They are developing the a technique to surround a primary beam with a second beam that acts as an energy reservoir, sustaining the central beam to greater distances than previously possible.
The secondary "dress" beam refuels and helps prevent the dissipation of the high-intensity primary beam, which on its own would break down quickly.
Water condensation and lightning activity in clouds are linked to large amounts of static charged particles. Stimulating those particles with the right kind of laser holds the key to possibly one day summoning a shower when and where it is needed.
http://www.science20.com/news_articles/ ... her-134522
A team from the University of Central Florida (UCF) College of Optics & Photonics and the University of Arizona are developing a technique to trigger rain and lightning in clouds with a high-energy laser beam.
The researchers have discovered that surrounding a laser beam with a second beam creates an energy reservoir that can sustain the central beam over long distances. This second “dress” beam helps prevent the dissipation of the primary, higher-intensity beam; alone, that primary beam breaks down, limiting its reach.
http://www.photonics.com/Article.aspx?AID=56102
Second article (and others) mention this is/was a DoD sponsored project.