In 1973, Laser Images Inc. in Van Nuys, CA, premiered its Laserium shows, which were greeted with enthusiasm by a mostly teenage audience. Laser entertainment has since found its way into a wide range of mainstream theme park, display, and advertising applications.
Until recently, however, entertainment laser users adapted products primarily intended for scientific or industrial applications. Now, a new generation of lasers is being employed in cutting-edge theme park applications.
High-power ion lasers are the type most widely used in entertainment. The two primary components are the laser head and the power supply (Figure 1). The head contains the plasma tube, magnet, mirrors, and the resonator, the mechanical structure that supports the mirrors. The plasma tube confines the inert fill gas, which is argon, krypton, or a mixture of both. The power supply produces an electrical discharge that ionizes the gas inside the plasma tube. The ionized gas (plasma) emits light that oscillates between the mirrors at each end of the resonator. The oscillation of light between the mirrors stimulates further emission of light.
By design, a small amount of this amplified light passes through one of the mirrors and constitutes the laser beam. This process of converting electrical energy to light energy is, unfortunately, inherently inefficient, and physics exacts its revenge in the form of heat, which must be removed continually by a water flow of several gallons per minute; otherwise, the plasma tube components would literally melt. Plasma tubes have a finite lifetime--they are a consumable quantity, and as such, most manufacturers make allowances for their replacement.
Lasers offer many unique and valuable properties. The laser delivers its light in one or more pure colors, which are extremely intense and visually appealing. Unlike the common laser pointer, ion lasers used for entertainment produce more than one wavelength (color) simultaneously. This is called multiline emission. The laser beam is therefore composed of several different colors that can be externally separated or combined by optical devices.
Argon ion lasers produce colors in the green, blue, and violet part of the spectrum, while krypton ion lasers generate colors in the green, yellow, and red. When a mixture of these two gases is used, the output beam spans the spectrum from violet to red. A mixed-gas laser of this type is commonly referred to as a white-light laser, because the mixture of the emission lines produces a white-colored beam.
Laser light is confined in a narrow beam that does not diverge appreciably over significant distances. Even though most ion lasers produce only a few watts of light energy, retaining the light in a small-diameter beam produces very high visual intensity. The "visual candy" of a typical laser light show is made up of scan patterns, lumia effects, and diffraction patterns, or combinations of all three.
Scan patterns are created by using electronically controlled galvanometer-mounted mirrors to deflect the beam across a projection surface. Acousto-optic modulators are used to select specific colors and/or vary the beam intensity (Figure 2). When a laser spot is scanned rapidly, the eye perceives a continuous image rather than a moving point of light. The speed of the beam deflection apparatus and the ability to modulate the light precisely offers an artist a great deal of flexibility to produce detailed, visually exciting images. Digital technology complements this capability by allowing the storage and playback of very long and complex sequences.
Lumia effects are created by passing the laser beam through an irregular material, such as rippled glass or plastic, resulting in diffuse, multicolored, cloud-like patterns. Lumia are sometimes used as the background for other effects. Diffraction patterns, which can be very complex, are geometric images caused by the interaction of a laser beam with a diffractive optical element, such as a diffraction grating or an array of pinhole apertures.
Because scientific and industrial usage constitutes the lion's share of the market for ion lasers, it's no surprise that most manufacturers have focused their product development on those sectors. Recently, however, ion laser manufacturers have begun to concentrate more on the entertainment market.
Entertainment applications do not usually demand the same level of beam quality. Generally, the primary concern in entertainment is obtaining usable amounts of light from several different wavelengths simultaneously. But obtaining adequate brightness from the red line of krypton when used in a mixed-gas configuration has been problematic for entertainment laser designers.
Another concern is the trade-off between output power and beam divergence. Relaxing a divergence specification may allow for higher output power and make the laser ideal for multimode fiber coupling, but if the same laser is scanned directly through fog or smoke, it may not be as visually appealing as a lower divergence laser with a lower output power.
Ivan Dryer, president of Laser Images, says, "In the early days of laser entertainment the major problems were short operating lifetimes (1,500 hours), plasma tube instability, and the need for virtually constant skilled maintenance." In 1981, however, improved tube lifetime and reliability was realized in Coherent Inc.'s introduction of Innova(r) metal-ceramic plasma tube technology.
The metal-ceramic design derives its name from the copper and tungsten metal bore-defining elements and the alumina ceramic envelope that confines them. The metal-ceramic design delivers the chemical and temperature resistance, thermal stability, and thermal conductivity necessary to ensure stable plasma tube lifetimes in the 5,000-hour range.
Coherent has also refined its overall product offering for entertainment by introducing the Enterprise(tm) II, Star(tm) II, and Sabre(r) laser systems. The Enterprise II PureLight(tm) is a small-frame ion laser designed for indoor installations. It features an output power specification of 1.2W in a mixed-gas white-light configuration. The Enterprise II PureLight delivers high output on a modest 208V single-phase input power, and can be cooled by a water-to-air heat exchanger, making it popular where the availability of cooling water is a problem.
Star II series lasers produce significantly higher power than the Enterprise II, and are suited for either indoor or outdoor use. Star II lasers are available in SkyLight(tm) Argon models with up to 6W of blue-green output power, SkyLight Krypton with 1.75W of red output power, and PureLight models with up to 3.5W of white light output. Low-divergence and red-enhanced models are also available.
Large-frame Sabre lasers are extremely high power and intended for outdoor installations such as theme parks, architectural lighting, and stadiums. Sabre lasers are available in SkyLight Argon models up to 30W output, SkyLight Krypton models to 6W output, and PureLight mixed-gas models to 13W output. Low-divergence models are available in each configuration.
Coherent's mixed-gas lasers address concerns about ocular perception from audiences. The human eye is sensitive to light in the spectral range from 380nm (deep violet) to 780nm (near infrared), with peak sensitivity around 555nm (green). The eye's sensitivity to the 514.5nm (green) emission line of the argon laser is approximately 10 times greater than its sensitivity to the 647.1nm (red) line of the krypton laser. To make red effects appear as bright to the viewer as green effects, red power must be increased. With the mixed-gas lasers, red enhancement is enabled by the precise control of gas pressure dynamics inside the metal-ceramic plasma tube. A metal-ceramic design maintains the red performance and the balance between the various colors without compromising the relative proportions of all the emission lines.
Laser output power is directly affected by mirror alignment, which can be altered by vibration, shock loading, or changes in ambient or cooling-water temperature. Mirror realigning requires some knowledge and experience with lasers, especially when misalignment is severe enough that the laser ceases to generate a beam of light. Coherent's "search-and-peak" feature uses internal light-regulation circuitry and motorized mirror mounts to achieve alignment on demand, even from a non-lasing condition. Maintaining optimum alignment means achieving maximum light output for minimum tube current, which also increases plasma tube lifetime.
Coherent mounts its mirrors on a rigid SuperInvar resonator. The high thermal mass and ultra-low thermal expansion coefficient of SuperInvar ensures superior long-term mechanical stability of the mirror alignment. Consistent output power, excellent beam-pointing stability, and a reduced need for realigning external optics such as galvo mirrors and modulators result.
Smoke and other aerosol environmental contaminants are part of the light show environment. Without protection for the internal optics, laser performance suffers, and the optics must eventually be cleaned to restore output power. Adding insult to injury, the system must be completely repeaked after any optical cleaning.
Innova metal-ceramic plasma tube design, however, has a sealed-mirror feature which hermetically seals the intra-cavity components and eliminates all cleaning requirements. The sealed-mirror design also removes a non-essential optical component from the laser cavity, further increasing reliability.
In the Sabre lasers, a vast amount of heat must be effectively dissipated to the cooling water. Precise control over the temperature, conductivity, and flow rate of the cooling water is paramount to the lifetime of the plasma tube. For this reason, the Sabre lasers include an integral water-to-water heat exchanger that protects the plasma tube even if the outside water supply is inconsistent.
Virtually all large laser shows and theme park installations are run under digital control, which eliminates the need to have a person make adjustments manually. All Coherent's entertainment lasers have digital interface capability. Status and maintenance information are also provided through the digital link, allowing service personnel located anywhere in the world to perform diagnostics and adjustments over phone lines.
Coherent's entertainment lasers have already helped show creators produce a new generation of spectacular displays at reasonable operating costs and with minimal requirements for trained personnel. Samsung's Everland theme park in Korea is the setting for a massive multimedia show created by Laservision of Dural, Australia.
The show venue is an outdoor area about the size of a football field which holds audiences of up to 10,000. An enormous rear-projection screen occupies one end of this space. In front of this screen is a 200'-wide (61m) fountain that produces an 80'-high by 160'-wide (24x49m) waterscreen. The boundaries of the show area are formed by adjacent park structures.
Laser components of the multimedia show include one Coherent Sabre PureLight 10W laser, three Sabre SkyLight Argon 30W lasers, three Sabre SkyLight Krypton 6W lasers, and five Nd:YAG lasers. Nd:YAG (Neodymium Yttrium Aluminum Garnet) lasers typically used in entertainment applications are flashlamp-pumped, solid-state, frequency-doubled, acousto-optically q-switched (pulsed) systems generating up to 60W average power in 532nm green. The high average power and visibility of the pulsed Nd:YAG laser make it a natural choice for certain atmospheric scanning effects. However, its single color output, oscillation at 20kHz, large beam diameter, and very high divergence seldom make it suitable for more sophisticated artistic effects.
Sixteen High End Systems Cyberlights(r), 60 High End Systems Dataflash(r) 1,200W strobes, 400 underwater lights, over 300 other theatrical lights, a Westrex 70mm film projector, 50 fog machines, a 72,000W Electro-Voice sound system, and various pyrotechnics complete the Everland installation. These elements are controlled from a central location by Laservision's proprietary hardware and software. Because of the scope of the project, the reliability and digital interfacing capability of the Coherent lasers were critical to its success.
During the show, effects are displayed on the rear-projection screen, the waterscreen, and the surrounding structures, creating a 3D illusion that completely immerses the audience within the fantasy. One of the major challenges in designing a show of this size and scope was to achieve adequate brightness for the various effects. Therefore, one pair of argon and krypton lasers is used for the rear-projection screen, and two additional pair are located in the wings; each pair of lasers generates a combination of red, green, and blue light. This format was necessary since a single large-frame mixed-gas laser did not meet the extremely high output power requirements of the installation.
The show begins with an animated waterscreen image of a god from ancient Korean mythology. This character "greets" the audience by shooting laser "bolts" at them; after this initial display of anger, he takes the audience on a fantastic journey, from a garden besieged by giant, laser-generated insects to a storm-tossed undersea tableau. To complete the underwater effect, a pattern of rippling laser light is projected on a ceiling of fog above the audience. Transitioning from inner to outer space, the audience then finds itself in the middle of a laser battle between spaceships. The rousing finale consists of an all-out assault on the audience using every available effect.
Laservision competed with organizations worldwide to win this contract and credits its success partly on its ability to produce a fully automated show that does not require highly trained on-site operators or maintenance personnel. The computer-controlled Coherent lasers, Cyberlights, and Westrex projector, together with Laservision's own Spectravision sequence editor were key ingredients in achieving this.
The ability to diagnose and fix system malfunctions remotely was also essential to Laservision's successful bid. Commands for either downloading laser diagnostic data or altering virtually any laser operating parameter can be issued by modem from the Laservision home office.
"While the initial purchase price of the Coherent lasers is higher than the competition, the long-term operating costs are lower due to 'hands-free' operation, greater lifetime, reliability, and the ability to perform remote diagnostics," says Simon McCartney, Laservision's export manager and senior producer.
Creating a laser display for the horticultural theme park Cypress Gardens in Winterhaven, FL, presented Redmond, WA-based Laser Fantasy International with an unusual problem. The show consists primarily of laser effects rear-projected onto a 35'-tall by 75'-wide (11x23m) waterscreen located in the middle of a lake. Two grandstands on the lake shore can seat 5,000. The problem was that park management did not want high-voltage AC power run from the show control center onshore out to the display area in the lake.
To power the waterscreen pumps, Laser Fantasy put a diesel generator on a pontoon platform in the lake. The lasers are located onshore, and their light is fed via underwater fiber optics to scanning and effects optics situated behind the waterscreen. The only underwater power line is low-voltage DC, which powers the scanners.
Using fiber delivery created two additional challenges for the show designers. First, there is an optical power loss of about 60% over the 300' (91m) of fiber which runs underwater; and second, the optical alignment of the laser beam and the fiber must be precisely maintained to get maximum laser power into the fiber.
To deal with the power loss, Laser Fantasy decided to use a pair of lasers to feed each fiber. This solution was both more reliable and more economical than using a single large laser. The answer to the alignment problem was to use Coherent Star PureLight lasers.
Other equipment used in the show includes a JBL sound system, two fog machines, a theatrical fan, 12 PAR lighting fixtures, and some pyrotechnics. Show control, including all the laser effects, is provided by Alesis ADAT digital tape decks, with some of the lighting and pyro effects run by an operator. Controlling the show via ADAT digital tape allows for both standardized production and implementation, as well as perfect control over artistic effects without on-site personnel.
The "Fantasy on the Lake" performance consists of a series of vignettes depicting a "Southern Belle" character and a butterfly named Flutter. Flutter's movement "paints" the sophisticated laser animations that comprise the bulk of the show. These animations use the multicolored argon/krypton lasers. Green YAG laser beams are used for framing and background effects. Additionally, YAG lasers are used to paint patterns on aerial fog above the audience.
"The combination of stability, reliability, and economy of the Coherent Star really helped us put this project together successfully," says Jeff Silverman, vice president of project development at Laser Fantasy. "Their sealed optics construction also means reduced laser maintenance, and lessens the need to adjust the critical fiber alignment."
The laser entertainment business, once virtually an afterthought for laser manufacturers, has now matured into a significant business segment. With laser display companies and various regulatory agencies, the International Laser Display Association (ILDA) works to ensure that increasingly spectacular and powerful outdoor displays like those described above remain safe not only for the audience, but also for commercial and general air traffic. As one can imagine, this is very serious business when the laser beams being used are powerful enough to be potentially harmful several miles from the show location.
The creation of fantastically complex laser displays is due in part to the advances in products engineered for the entertainment user. Does this mean that an even more exciting generation of dazzling shows and attractions is on the horizon? Given the talent and drive of the laser display industry, I don't think audiences will have a long wait!