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Show Basics: Projectors

Getting to Know Your Projector
By Patrick Murphy, Pangolin Laser Systems
(This is an excerpt of a more detailed article available at:

The first requirement for a laser show is, of course, a laser. There are three general types of light show graphics lasers: low power helium-neon (red), and medium and high power argon (green-blue) or mixed gas argon/krypton (red-yellow-green-blue).

The power you need depends on whether you're concentrating on beams or graphics, and on the scope of your shows -- for small or large audiences.
Low power HeNe lasers are fine for studio work and small-scale indoor graphics. Medium power lasers use standard 110 volt AC power and are air-cooled by fans. They can handle many indoor graphics, and small-scale indoor beam effects. High power lasers need 220 or 440 volts and require water cooling using hoses or chillers. They are for large-scale indoor graphics, outdoor graphics and beam effects.

Usually, a laser projector will work with just about any laser. Therefore, if your emphasis is on graphics, spend less on the laser initially and more on the projector and computer system. This is because you can later rent or purchase a more powerful laser for your existing projector. If your emphasis is on beam effects, spend more on the laser to get the maximum possible brightness. You want as much power as possible so beams show up even under adverse conditions, such as outdoor shows in high-brightness areas.

A popular laser for beams is based on frequency-doubled YAG technology. YAGs are great for beams, but are poorly suited for graphics as they have larger diameters and usually are not continuous. (Scanned graphics may have fat, dotted lines.) If you are buying only one laser for both graphics and beams, stick with continuous-wave gas laser technology such as argon/krypton.

You can purchase new or used lasers. Probably the best value is a used laser which has been re-gassed or re-tubed by a company specializing in this work. Warranties are available from reputable used laser dealers.

Laser projectors
T he laser projector includes a pair of galvanometer scanners, a blanking or color system, and related electronics. You can either buy a fully assembled laser projector, or put together your own projector.
Fully assembled projectors are usually made on a semi-custom basis. The manufacturer will design a system with components matched for your particular requirements. Full-color (PCAOM-based) graphics projectors start at around $7500. Adding beam tables and lumia effects quickly raises the cost. If you are technically minded, you can buy the projector components and assemble them into a system. This is an especially attractive approach for those on a budget with relatively simple needs, or for those who have previous experience with laser projectors.

Before going into detail on the projector parts, let's look at the final components of a laser system: the computer and software.

Computer and software
Laser show software is available for almost every personal computer, from the Amiga and Macintosh to IBM PC compatibles. There are even programs with their own custom computers. Look for the software first; this will help narrow down your choice of computer.

There are three general levels of software: hobbyist, intermediate and professional. Roughly speaking, price ranges are under $1000 for the hobbyist level, $1000-5000 for intermediate, and above $5000 for professional. This may seem costly in comparison with spreadsheets or word processors. But remember that the market for laser show programs is much more limited.

As with all software, the more expensive programs give you more features, a friendlier user interface and better service and support. Be sure to choose software that meets your needs, both for now and for the future.

The laser projector is the heart of a graphics system. It contains the galvanometer scanners and scanner amplifiers, which together move the beam fast enough to create graphics. It also contains an intensity device that blanks and/or colors the laser beam. This section discusses these two vital parts of a projector. There can be other parts, such as beam tables and lumia special effect devices. However, this section will concentrate on the graphics-specific parts, since graphics are vital to today's laser shows.

Here's some essential information on what's necessary to put together a good graphics projector:

X-Y scanners
Scanners move tiny (3 x 5 mm) mirrors that deflect the beam. Two are needed; one for horizontal motion (X) and one for vertical (Y). Together, they can position the beam anywhere on the display screen.
For the most accurate graphics reproduction, use closed-loop galvanometer scanners (they're also called "position-detecting" scanners).

The mirrors and mirror mounts for the scanners may be included with the scanners, or may be priced separately. You also need a positioning mount. This holds the scanners at right angles to each other, in the best orientation for X-Y scanning. You can purchase this or machine your own.

Scanner amp
Each closed-loop galvo scanner requires a closed-loop scanner amplifier to condition and amplify the computer's laser control signals. You can obtain the amplifiers either as circuit boards or as fully assembled units. Circuit board amps use trimpots for control adjustments, and require a power supply, usually +/-15 VDC or +/- 24 VDC at 2 to 4 amps. Fully assembled amps come in a case with 110 volt AC power supply and knobs to adjust controls. An advantage of boards is that you save money and you can mount them inside your projector chassis, avoiding another box to carry around.

A cable connects the boards to the scanners. You can purchase this or make your own. The cable is usually short, to provide the most accurate feedback signals between the scanners and the amp.

Before you buy
Before you buy scanners, be sure you know exactly what you're getting. For example, you may see ads for "abstract graphics" projectors. This term means that the projector is not intended for accurate computer control. It usually uses open-loop scanners with simple amps. Also avoid resonant scanners; these scan only simple patterns at fixed frequencies.

Incidentally, used scanners of any type are often a wise buy -- if you know the scanners are in good condition. Should you be purchasing new scanners, note that there is often a backlog. Lead times can be as much as ten weeks.

Single-color control
Most graphics projectors use some type of blanking device, to turn off the laser's beam as it moves between the visible lines of a drawing. Blanking in a single-color projector can be done with a galvo scanner or with an acousto-optic modulator (AOM) crystal.

The advantage of galvo blanking scanners is their compatibility with galvo mirror scanners. Their on/off response time inherently synchronizes with the galvo mirrors' movements. The disadvantage is that this response time is relatively slow. It is not enough to simply use an arm which rotates in and out of the beam. Complex, multi-mirror optical paths are required, so that a small movement of the blanking galvo can instantly cut off the laser beam.

AOMs operate much faster than galvos, automatically giving clean on/off response. Many people feel they are easier to work with, since they do not require the optical path lengthening of galvo blanking. However, timing adjustments are necessary in the laser software or in the AOM driver circuit so that the AOM is synchronized with the much slower X-Y scanners.

Full-color projectors
A white-light laser beam enters the PCAOM crystal from the right, while a radio-frequency signal is injected from the top. The RF signal sets up a diffraction pattern which acts as a prism.
The result is two beams exiting on the left: the desired color and a "waste" beam with all colors except the desired color. Since 1992, most full-color projectors use polychromatic AOMs (PCAOMs). These control both blanking and color selection in one device. They are usually used with so-called "white-light" beams to do full-color graphics.

You can create a white-light beam on a budget by using an air-cooled argon and a helium-neon laser. The two beams are mixed using a dichroic filter into a single white-light beam containing red (HeNe) plus green and blue (argon). For more power and convenience, select a mixed-gas laser. This will provide white light (either red-green-blue or red-yellow-green-blue) in a single beam.

Color balance is important, so be sure your beam has a good mix of colors to make a balanced white. Because the eye is more sensitive to green, there should be more red and blue light than green.
In a PCAOM system, a white-light beam is directed into a crystal. Signals from the computer go into the PCAOM driver, which causes the crystal to diffract different wavelengths (color) away from the original beam. The diffracted, colored beam continues on to the X-Y scanners.

PCAOM driver electronics come in 4-, 6- or 8-channel models. This refers to how many wavelengths (colors) can be simultaneously controlled. Usually, the more channels the better. For example, Pangolin's LD Pro controls up to six channels. This lets you create unique colors such as a pure violet. It is not a mixture of red and blue, but it is the argon's natural violet wavelength coming through.

PCAOMs have become the de facto method of color control. This is because they are simple to align, relatively inexpensive, and provide extremely fast control. PCAOMs are so fast that each point in an image can have a different color. (One benefit of this speed is that TV-like raster images can be created.)
Even if you don't have a white-light laser beam, you may still want to consider a PCAOM. It can give higher throughput since it will modulate all available wavelengths (such as the greens and blues in an argon laser). And, you can move up to full color at any time, simply by using a white-light beam as input to your projector.

Basics and add-ons
Here are some suggested system configurations. Costs given are only for the parts in a graphics projector; they do not include the projector chassis, laser or computer.

If you're a hobbyist on a very tight budget, start with a simple two-scanner system. One scanner controls the X (horizontal) axis, the other controls the Y (vertical) axis. At a minimum, you will need: two scanners with mounted front-surface mirrors, a mount to position the scanners relative to one another, two single-channel scanner amps (or one dual-channel amp), a power supply for the amp(s), and a cable to connect the amps and scanners.

To give an idea of costs, the above is about $2000 using the fastest available scanners, Cambridge Technology model 6800. Cambridge provides everything except the power supply.

The system above will not have blanking. Although it is possible to do clever drawings which hide the retrace line, most people should also add a blanking or color control device. It is certainly easier to create images when you can hide the beam. A blanking projector adds a blanking device (galvo or AOM), a driver (scanner amp or AOM driver), a bracket to hold the device in position, and a power supply for the driver. Expect to pay roughly $1000 for a monochrome blanking device and driver. A PCAOM can be the best way to go. At a cost of $1000 - $3000, it serves not only to blank the beam, but to control color of all but the highest power laser beams. Having a PCAOM gives you great flexibility to move up in power and capabilities without buying any new equipment.

The costs given above do not include a chassis. One important reason to buy a fully assembled projector is that the manufacturer provides the chassis plus additional convenience and safety features, such as a shutter. In the United States, the manufacturer should also provide CDRH certification.

This last item means that the projector has been built to the standards of the U.S. laser safety agency, the Center for Devices and Radiological Health. If you perform public shows in the U.S., you must certify both your equipment and show sites to the CDRH. Most manufacturers of complete, turnkey projectors will include equipment certification as part of their service.

Patrick Murphy is president of Pangolin Laser Systems, past president of ILDA, and currently services as ILDA's Air Space Issues Coordinator.


Additional Show Basics Links





X-Y laser scanners by Cambridge Technology Inc.

Ion lasers and power supply by Spectra Physics