Zeeya Merali

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 (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.

Rainmaker

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. 

• References
  1. Rohwetter, P. et al. Nature Photonics advance online publication doi:10.1038/nphoton.2010.115 (2010).
  2. Kasparian, J. et al. Opt. Express 16, 5757-5763 (2008). | Article

Source : naturenews

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 Laserist

SCIENTISTS are using the world’s largest laser in an attempt to build a star on Earth.

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.

Nerd alert – inside the target there’s a couple of reactive hydrogen isotopes, so you know what comes next.

The heat from the laser will fuse those isotopes together in reaction that at 100 million degrees Celsius, more than five times hotter than the centre of the sun.

There is a slight radioactive danger, but the lab has encased the facility in concrete walls that are two metres thick, just in case.

But the payoff is that if the isotopes fuse, the tiny star will emit enough energy to power the Earth.

That is, for the 200 trillionths of a second that it survives.

“It’s the most fundamental energy source in nature,” project manager Bruno Van Wonterghem told CNN.

The only fuel it requires is seawater, the source of the aforementioned isotopes.

If it’s successful, the laboratory hopes the project, which has so far been five years in development and cost more than $2 billion, will deliver useable outcomes within 20 years.

“This is something you’re going to tell your grandchildren about,” Mr Van Wonterghem told CNN.

“It’s like standing on the hill watching the Wright brothers’ plane go by.”

Source : news.com.au

Patricia Daukantas

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.

Anyone can create a crude version of a laser show: Just aim the beam of a laser pointer at the wall and quickly shake your hand side to side to create a colored line. Today’s laser projectors basically do the same thing, only faster and with more precision. They contain prisms, mirrors and other components that laser-show pioneers would have had to have set up by hand.

To produce pictures on a screen or wall during a laser show, two galvanometers—dubbed “galvos” in the industry—use electrical signals to make small mirrors vibrate over a two-dimensional plane. The moving mirrors reflect the beam path fast enough to trace a shape on a target wall or screen. In the trade, this process is called “scanning.”

Simple 2-D manipulations of the mirror make the laser trace the familiar Lissajous figures of complex harmonic motion. Another galvo—or, in some modern projectors, an acousto- or electro-optic modulator—can move a second mirror to deflect the beam to the side, so that it doesn’t exit the projector. This type of modulation is known as “chopping,” and it’s the laser-show equivalent of lifting a pencil from the paper. Similarly, “blanking” modulates the beam by turning the laser on and off rapidly. Chopping and blanking separate line segments, curves and letters of the alphabet.

Laser displays are best suited for drawing outlines of familiar shapes, resulting in cartoon-like images. Today’s laser artists use graphics software to draw the logo or picture they want to reproduce, and then a specialized program translates the image into commands for moving the laser beam with a refresh rate of 15 to 30 Hz, thanks to the persistence of vision of 40 ms (25 Hz). For comparison, most theatrical films run at 24 Hz.

Laser artists can also create “atmospheric” or beam effects, in which the audience can see the laser beams as they move through the air, thanks to Rayleigh scattering. The artist usually uses theatrical fog or smoke from pyrotechnics to create this effect. Sometimes ambient dust will suffice if the beams are very powerful.

“Lumia” is the collective term used for the textured glass or plastic filters that are used to distort the outgoing laser beam into abstract shapes. Galvos and motors usually move these filters to the laser artist’s specifications. Diffraction gratings, both stationary and movable, cause the light to form multiple beams.

Laser art and the far-out 1960s

In the late 1960s and early 1970s, artists and scientists collaborated on projects for exhibits and concerts on both sides of the Pacific. Many fertile minds, some trained in art and others in science, were eager to explore the visual possibilities of the new medium.

It is difficult to define when the first laser show or laser-art exhibit took place. “The closer you look at it, the fuzzier it gets,” said Patrick Murphy, executive director of the International Laser Display Association (ILDA), a trade association for laser display companies.

An artist named Lowell Cross started visualizing electronic music as a graduate student at the University of Toronto in the mid-1960s. At first he connected an RF modulator to a television receiver to interpret his own music as well as the works of composers John Cage and David Tudor. In 1969, Cross and University of California at Berkeley laser physicist Carson D. Jeffries collaborated on a visual project, and the resulting public performance of sound and music at Mills College in Oakland, Calif., used multiple laser colors with 2-D scanning.

Around the same time, a Washington D.C. sculptor named Rockne Krebs joined a group of artists who were experimenting with the bold colors of acrylic paint. In 1967, Krebs purchased a He-Ne laser and then worked with a University of Maryland scientist to figure out how to use it. After designing a 1968 exhibit of one laser and two mirrors at a Washington art gallery, he wound up working alongside Hewlett-Packard engineers in Palo Alto, Calif., on a display destined for Expo ’70, the world’s fair near Osaka, Japan.

That futuristic international exposition attracted a collective group called Experiments in Art and Technology, or E.A.T., whose members brought their cross-disciplinary optical experiments into the public spotlight. The Pepsi Pavilion at Expo ’70 contained the world’s largest spherical mirror—which was made of aluminized Mylar and spanned 90 feet across. In the main hall, visitors could see their reflections hanging upside down above their heads. To get to that hall, they walked through a dark clam-shaped room illuminated by sound-activated laser beams shining downward and tracing Lissajous figures on the floor. E.A.T. commissioned Cross and Jeffries to design the laser-and-sound display.

An estimated 2 million people visited the Pepsi Pavilion during the six months of Expo ’70. However, according to Cross’s website, company officials were not able to maintain the technical exhibits to the artists’ standards, and the building was demolished soon after the exposition ended. Cross moved to the University of Iowa and created a mixed-gas argon-krypton ion laser show—complete with symphony orchestra, soloists and electronic music—for the opening of a new campus auditorium in 1972.

Source : OPN

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.

WADIMOS partners will present their results at this week’s Photonics Europe conference in Brussels, which runs 12–16 April.

The enormous computing power of multi-processor systems and manufacturing tools being considered will require data transfer rates of more than 100 Terabit/s. These data rates may be needed on-chip, e.g. in multi-core processors, which are expected to require total on-chip data rates of up to 100 TB/s by 2015, or off-chip, e.g. in short-distance data interconnects, requiring up to 100 TB/s over a distance of 10–100 m. Optical interconnects are the only viable technology for transmitting these amounts of data.

Besides a huge data rate, optical interconnects also allow for additional flexibility through the use of wavelength division multiplexing. This feature may help realizing more intelligent interconnect systems such as the optical network-on-chip system that the WADIMOS project also is studying.

WADIMOS will build a complex photonic interconnect layer incorporating multi-channel microsources, microdetectors and different advanced wavelength routing functions directly integrated with electronic driver circuits. It also will demonstrate the application of the electro-photonic ICs in an on-chip optical network and a terabit optical datalink.

Source : optics.org

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.

The WestJet flight had just taken off from Calgary, bound for Kelowna, B.C., on Oct. 3, when a green laserbriefly lit up the cockpit, said WestJet official Scott Wilson.

The first officer looked out to see where it was coming from and was hit directly in the eyes. The crew member did not suffer any permanent damage, which could jeopardize a pilot’s career. “As soon as they got to [the] destination, we had them off-loaded from the aircraft and report to emergency for a proper ophthalmologic exam,” said Wilson. “And we actually had one more followup when they returned to Calgary a day later.”

Wilson said powerful laser pointers are widely available and safe to use according to their instructions. But he warns that the police take incidents where a plane is being tracked with a laser very seriously, especially when planes are landing or taking off.

“I don’t know if the individuals that are perpetrating such things truly understand the danger of the laser versus it’s kind of fun to point a light at the aircraft. But you know, anything that can cause long-term ill effects to our employees or our guests causes us concern, great concern quite honestly.”

Transport Canada said it has received 73 reports of bright lights being shone into cockpits from the ground since 2005. David Mackow pleaded guilty earlier this year to breaching the Aeronautics Act after an Air Canada Jazz pilot was distracted by a green laser beam while landing in Calgary on Oct. 15, 2007. The laser beam came from an apartment in the city’s downtown core.

The pilot reported the incident and Calgary police dispatched its HAWCS helicopter to investigate. Mackow, a forklift operator, then pointed the green beam into the helicopter.

Mackow told police he was “just having some fun,” but was fined $1,000. Court records show that he later expressed remorse for his actions.