Lasers that stimulate condensation may help to induce rain artificially.

Zeeya Merali

Make rain while the laser shines.J-P. Wolf / University of Geneva

The rain dance is getting a twenty-first-century revamp using laser technology. Optical physicists have demonstrated that shooting lasers into the air can trigger the formation of water droplets, a technique that could one day help to stimulate rainfall.

For more than 50 years, efforts to try to artificially induce rain have concentrated on ‘cloud seeding’ — scattering small particles of silver iodide into the air to act as ‘condensation nuclei’, or centres around which rain droplets can grow. “The problem is, it’s still not clear that cloud seeding works efficiently,” says optical physicist Jérôme Kasparian at the University of Geneva, Switzerland. “There are also worries about how safe adding silver iodide particles into the air is for the environment.”

Kasparian and his colleagues realized that there might be a more environmentally friendly alternative. Firing a laser beam made up of short pulses into the air ionizes nitrogen and oxygen molecules around the beam to create a plasma, resulting in a ‘plasma channel’ of ionized molecules. These ionized molecules could act as natural condensation nuclei, Kasparian explains.

To test whether this technique could induce droplets, the researchers fired a high-powered laser through an atmospheric cloud chamber in the lab containing saturated air. They illuminated the chamber using a second, standard low-power laser, enabling them to see and measure any droplets produced. Immediately after the laser was fired, drops measuring about 50 micrometres wide formed along the plasma channel. Over the next three seconds, the droplets grew in size to 80 micrometres as the smaller droplets coalesced. The team’s results are published online in Nature Photonics (www.nature.com) Continue reading Rain-making lasers could trigger showers on demand