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Lasers that stimulate condensation may help to induce rain artificially.
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 (see video). 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 Photonics1.
The next step for Kasparian and his team was to take the technique outside. The researchers already have experience using plasma channels to modify the weather: in 2008, they demonstrated that a beam from their high-powered portable ‘Teramobile laser’ could be fired into thunder clouds, triggering an electric discharge2. The beam was able to reach its target without being deflected because the generated plasma channel modifies the speed at which light travels through air — slowing it down in the centre of the beam and speeding it up at the sides. This causes the beam to continually self-focus, helping it to maintain a high intensity across large distances (see ‘Bendy laser beam fired through the air’).
This time, Kasparian and his colleagues tested the Teramobile laser over a number of different nights and in various humidity conditions. Once again, they detected the amount of condensation induced by monitoring how much the light from a second laser was back-scattered by any droplets. In low humidity conditions, the Teramobile laser did not induce droplets. But when the humidity was high, the team measured up to 20 times more back-scattering after the Teramobile laser was fired than before, says Kasparian, suggesting that condensation droplets were forming.
However, the technique is still in its early stages. “We can only create condensation along the laser channel, so we won’t be going out and making rain tomorrow,” Kasparian notes. He and his team are now investigating whether they can create condensation over a wider area, by sweeping their laser across the sky.
Thomas Leisner, an atmospheric physicist at the Karlsruhe Institute of Technology, Germany, remains cautious about the feasibility of scaling up the technique in this way. “I am sceptical that this could be used to trigger rain on demand,” he says. But he adds that the technology will have other uses. The researchers should now calibrate the relationship between the amount of condensation produced by the laser and the prevailing atmospheric conditions, he says. “They could use the amount of condensation produced by their laser as a measure of water saturation to help forecast the chance of rain,” he says.
- Rohwetter, P. et al. Nature Photonics advance online publication doi:10.1038/nphoton.2010.115 (2010).
- Kasparian, J. et al. Opt. Express 16, 5757-5763 (2008). | Article
Source : naturenewsRead More
LOBO electronic recently premiered its first interactive laser show at Germany’s Holiday Park. LOBO’s Alex Hennig said the show worked better than expected, with thousands of audience members eagerly responding to the commands of a laser-projected girl.
The show, performed this summer in the theme park’s Aqua Stadium, featured a floating water screen, four laser systems, and 18 fog generators. The laser-projected girl gave the audience instructions (such as waving hands, clapping, and singing along to the music). “Surprisingly, the audience really followed even the most demanding actions and this concept really had a booster effect,” said Hennig. To add more excitement, the audience was given small battery-powered fiber lamps that turned the audience area into a sea of moving lights.
Source : The LaseristRead More
The laser at the Lawrence Livermore National Laboratory is roughly the size of three American football fields, and those in charge of it aren’t joking when they say they’ll create a tiny sun in the next few months.
It’s called the National Ignition Facility and it’s all about finding the holy grail of energy production – nuclear fusion – a high-energy reaction that would theoretically provide limitless energy for humanity.
In a nutshell, the laboratory hopes to split its laser beam up into 192 beams, then fire them at a tiny target wrapped in gold that’s smaller than a fingernail.Read More
For almost as long as visible-wavelength lasers have existed, artists have been inspired by their potential to create stunning visual displays.
As the clock ticked toward the end of the first half of Super Bowl XLIV, two teams huddled on the sidelines, waiting for the signal. Each had a single objective and a tight timeframe for achieving their goal.
But they weren’t looking to score a touchdown. Rather, these teams were the special-effects technicians for the halftime show. They had nine minutes to ensure that 16 powerful lasers were hooked up and safely aligned to a 40-section platform in preparation for a laser show to accompany the performance of the rock group the Who.
More than 100 million people watched the Feb. 7, 2010, performance on television, making it one of the most-viewed laser shows ever. The special effects teams set up two “laser compounds,” one at each 35-yard line on the New Orleans Saints’ side of the gridiron. Each compound had two 50-W Nd:YAG pulsed lasers, cooled with a recirculating-water chiller, plus two air-cooled, full-spectrum units: a 25-W optically pumped semiconductor (OPS) laser and a 13-W diode-pumped solid-state (DPSS) RGB laser.
Laser shows have always held a universal appeal. People from all over the world have enjoyed them at planetariums, concerts, corporate meetings and other venues. In the United States, outdoor laser displays dance across the faces of the Grand Coulee Dam in Washington and Stone Mountain in Georgia. They illuminate the pyramids of Giza in Egypt and the night sky above the Hong Kong business district. Coherent beams of color formed pictures of Olympic athletes against the side of the Sydney Opera House in 2000, and, at the 2010 Olympic Winter Games in Vancouver, 20 lasers were used in a nightly light show in which people from around the world controlled the beams through public Internet access.
How laser shows work
The stunning visual effects of laser shows rely on some of the simplest optical equipment and principles: moving mirrors and the effect known as persistence of vision—which refers to the afterimage that persists when a point of light moves faster than the eye can react to it. The afterimage lasts for roughly 1/25 of a second.
A European project unveils a fully CMOS-compatible laser source coupled to a silicon waveguide.
A team of researchers from across Europe will present details of a fully CMOS-compatible laser source that is coupled to a silicon waveguide this week. The achievement is a major milestone in a three-year €3.2m project known as WADIMOS (Wavelength Division Multiplexed Photonic Layer on CMOS). The ultimate goal of the project is to demonstrate a photonic interconnect layer on CMOS.
WADIMOS, an EU-funded research project, started in January 2008 and has six project partners. It is co-ordinated by IMEC of Belgium and also involves STMicroelectronics, MAPPER Lithography, Lyon Institute of Nanotechnologies (INL) and the University of Trento.
Working with a circuit design from INL and IMEC, LETI completed the specific process studies for the laser source by adapting and modifying standard III-V materials process steps to comply with a CMOS environment. Specifically, LETI replaced gold-based metal contacts with a Ti/TiN/AlCu metal stack. The circuits were processed on 200 mm wafers at LETI’s facilities.Read More
Green Event at the Key Club – April 10, 2009Read More
Transport Canada and police are investigating a complaint that a WestJet pilot was hit in the eye with a green laser beam while his plane was taking off from the Calgary airport, CBC News has learned.
This is at least the fourth incident this year where someone has used a hand-held laser pointer to target a plane leaving from, or arriving at, the Calgary airport.