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