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AMAZON multi-meters discounts AMAZON oscilloscope discounts Want to put on a neighborhood light show that will dazzle your friends and family? Considering going into the professional laser light show business? Or just interested in experimenting with new art forms? The projects described in this section can turn you into a light show wizard. You’ll learn how to make complex geometric patterns using devices known as galvanometers. You’ll also find details on making your own galvanometers and the basics of how to effectively use argon and krypton lasers in light shows. Finally, this section provides important information on restrictions and rules governing public light show performances. WHERE TO HAVE A LIGHT SHOW Before discussing the how’s of advanced light shows, let’s take a moment to examine where to have them. Your choice of location goes a long way toward the overall enjoyment of the show and the ease with which you can produce it. You must consider the size of the room or auditorium, the location of screens or backdrops, the degree of light-proofing for doors and windows, and several other factors. Even high-powered lasers look dim when they are used to create flashing beams and undulating light forms on the screen. A truly professional light show uses high-powered 2- to 5-watt argon and krypton lasers that cost $35,000 to $80,000. Unless you find one of these that has fallen off some truck (in which case you probably don’t want it), you’ll be using a trusty red helium-neon laser for your light shows. The higher the output of the laser, the brighter the beam. However, note that a 10 mW laser might not necessarily appear twice as bright as a 5 mW laser. Beyond a certain level the eye can no longer discern brightness. But the higher output tube will deliver more light as the beam is swept across the screen. Speaking of screens, you must provide some type of light colored background or the laser beam may not be clear or easy to see. A beaded glass screen designed for movie projection isn't a good idea because the little beads of glass act as prisms and mirrors. Not only will the beam be reflected back into the audience, it will appear fuzzy due to dispersion inside the glass. Any light-colored wall, preferably one painted with flat white paint, will do. If such a wall isn't handy, bring one in the form of a well-pressed sheet, a piece of photographic background paper (this stuff comes in convenient rolls), or a scenery flat. A flat, used in live theater, is a piece of painted muslin stretched taut in a wood frame. The flat is lightweight, but its size makes it hard to transport. Obviously, the room or auditorium must be large enough to accommodate the number of people attending the show, but it must also be spacious enough to allow the light show pattern to spread to a respectable size. The distance between the laser and the projection surface is called the throw. The longer the throw, the larger the light show image. An image that's 1 foot high at a distance of 6 feet will measure 2 feet high at a throw distance of 12 feet. An easy rule of thumb is that every time you double the throw, the image size increases by 100 percent. Because the laser beam is so compact, the effects of the inverse square law are minimized (recall from Section 3 that the inverse square law requires the intensity of light to fall off 50 percent for every doubling of light-to-subject distance). It doesn’t really matter if the laser is 10 feet from the wall or 20 feet, but remember the effects of a long throw. Too much distance can cause the light show patterns to fan out excessively. Beam divergence also becomes a problem at long distances. A laser beam with a divergence of two milli-radians will diverge to a spot approximately two inches in diameter at 80 feet. How will you seat the audience? The conventional chairs- facing-the-screen seating arrangement is only marginally useful in laser light shows. Projecting the laser beam like a movie image requires that the laser projector be placed high above the audience, and your room might not easily allow for this. EXPERIMENTS WITH GALVANOMETERS Professional light shows don’t use R/C servos or stepper motors as laser beam scanners. Rather, they use a unique electromechanical device called the galvanometer. A galvanometer—or galvo for short—provides fast and controllable back-and-forth oscillation. Mount a mirror on the side of the shaft and the reflected light forms a streak on the wall. Position two galvanometers at a 90-degree angle, apply the right kind of signal, and you can project circles, ovals, spirals, stars, and other multi-dimensional geometric shapes. What is a Galvanometer? Most electronics buffs are familiar with the basic galvanometer movement of an analog meter. The design of the movement is shown in ill. 20-1. A coil of wire is placed in the circular gap of a magnet. Applying current to the coil causes it to turn within the electromagnetic field of the magnet. The amount of turning is directly proportional to the amount of current that's applied. The needle of the meter is attached to the coil of wire. ill. 20-1. The basic operation of the galvanometer. Some meter movements are designed so that the needle rests in the center of the scale. Applying a positive or negative voltage swings the needle one direction or the other. Say that at full deflection the meter reads + and —5 volts. When charged with + 5 volts, the needle swings all the way to the right. When charged with —5 volts, the needle sways all the way to the left. Current under 5 volts (positive or negative) causes the needle to travel only part way right or left. Meter movements are designed for precision and are not capable of moving much mass. But by using a stronger magnet and a larger coil or wire, a galvanometer can be made to motivate a larger mass. Heavy-duty scanning galvanometers are often made to actuate the needles in chart recorders and they have more than enough “oomph” to rack a small first-surface mirror back and forth. Some galvo manufacturers, most notably General Scanning, make units specifically designed for high-speed laser light deflection. These are best suited to laser light show applications but their cost is enormous. Surplus galvanometers, available from several sources including Meredith Instruments, Fobtron Components, and General Science and Engineering, cost from $660 to $320 apiece; new high-speed models cost upwards of $950. You may use either commercially made galvanometers for the projects that follow or make your own using small hobby dc motors. Be aware that commercially-made galvos work much better than homemade types, but if you are on a budget and simply want to experiment with making interesting light show effects, the dc motor version will prove more than adequate. Using Commercially-Made Galvos Ill. 20-2 shows a typical commercially made galvanometer. The General Scanning model GVM-735 galvanometers illustrated in the picture are actually Cadillacs among scanners, so the units are not representative of typical quality. There are other makers of fine galvanometers, including C.E.C., Minneapolis-Honeywell, and Midwestern. Galvanometers carry a number of specifications you can use to judge quality, versatility, and practicality. Among the most useful specifications are: * Rotation. The amount of deflection of the shaft, in degrees. Usually stated in both + and — about a center point. A deflection of 10 to 20 degrees is fine for light show applications. * Natural frequency. Often stated as the resonance frequency, in hertz, and provides an indication of top speed. Most galvo applications call for a top frequency of 80 percent of the resonance frequency. E.g., with a resonance frequency of 225 hertz, top operating frequency is about 180 Hz. * Rotor inertia. The measurement of the ability to move mass. A higher inertia means the galvanometer can move a greater amount of mass. The rotor inertia is relatively small—1 to 2 g/cm but it’s sufficient to move a small, mounted mirror. * Coil resistance. The resistance, in ohms, of the drive coil. Helpful in designing and applying drive circuits. * Operating voltage. Nominal and /or maximum operating voltage, typically 12 volts. Also useful in designing and using drive circuits. ill. 20-2. A commercially made precision galvanometer. * Power consumption. The power consumption, in milliamps or amps, of the galvanometer, typically under worst-case conditions (full rotor deflection, full voltage, etc.). The drive circuit you use must be able to deliver the required current. Driving Galvanometers Galvanometers can be driven in a variety of ways, including power op amps, audio amplifiers, and transistors. A basic, no-frills drive circuit appears in ill. 20-3 (refer to TABLE 20-1 for a parts list). The input can be an audio signal from the LINE OUT jack of a hi-fl or an unamplifled input from a frequency generator (more on these later). You can apply an amplified signal to the input of the drive circuit, but the op amp will clip the output if the input is excessively high. The two drive transistors, a complementary pair consisting of TIP31 and T1P32 power types mounted on heatsinks, interface the output of the op amp to the coil of the galvanometer. The circuit works with a variety of voltages from ± 5 volts to ±18 volts. Most scanners operate well with supply voltages of between ± 5 and ± 12 volts. Check the specifications of your galvanometers and make sure you don’t exceed the rated voltage. If anything, operate the galvos at a reduced voltage. They will still operate satisfactorily but the rotor might not deflect the full amount. This isn't a problem for most applications, including laser light shows, where full deflection isn't always desired. ill. 20-3. Driver circuit for operating a galvanometer from line-level audio source. Build two circuits for controlling two galvanometers. Notes: Q1 and Q2 must be on heatsinks! Use supply voltage to complement galvanometer; up to ± 18 VDC. Table 20-1. Galvanometer Drive Parts List
All resistors are 5 to 10 percent tolerance, ¼ watt. One by-product of full deflection is a “ringing” that occurs when the rotor hits the stop at the ends of both directions of travel. The ringing appears in the laser light form as glitches or double-streaks. To make two-dimensional shapes, you need two galvanometers positioned 90 degrees apart, as illustrated in ill. 20-4. Mount mirrors on the shafts using aluminum or brass tubing. Add a set screw (see ill. 20-5) so that you can tighten the mirror mounts on the rotor shaft of the galvanometer. You can use any number of mounting techniques to secure the galvos to an optical breadboard or table, but the mounts you use must be sturdy and stable. Vibrations from the galvos can be transferred to the mounts, which can shake and disturb the light forms. ill. 20-4. How to arrange two galvanometers to achieve full X and Y axis deflection. Place the mirrors of the galvanometers close together to counter the effects of beam deflection. Set screw ill. 20-5. You can mount a thin, front-surface mirror to the galvanometer shaft using an aluminum spacer that has been filed down. Galvo shaft Build a separate drive circuit for both galvanometers and enclose it in a project box (or you can include the driver circuit in a larger do-everything light-show console). I built the prototype drive circuit on a universal breadboard PCB and had plenty of room to spare. The enclosure measured 4¾ by 7¾ by 2¾ inches. Subminiature ½-inch phone jacks were provided for the audio inputs and scanner outputs and potentiometers were mounted for easy control of the input level. To test the operation of the galvanometers and drive circuits, plug in the right and left channels of the hi-fl and turn the gain controls (R1 for both drives) all the way up. The galvos should shake back and forth in response to the music. Shine a laser beam at the mirrors so the light bounces off one, is deflected by the other, and projects on the wall. The light forms you see should undulate in time to the music. Providing an Audio Source The test performed above only lets you test the operation of your galvanometer setup. With the arrangement detailed above, the light form will always be squeezed into a fairly tight line that crawls up and down the wall at a 45-degree angle. Full flexibility of a pair of galvanometers, physically set apart 90 degrees, requires an audio source that has two components — both of which are set 90 degrees apart in phase. Audio signals are sine waves, and sine waves are measured not only by frequency and amplitude but by phase. The phase is measured in degrees and spans from 0 to 360 degrees. Ill. 20-6 shows two sine waves set apart 90 degrees. Notice that the second wave is a quarter step (90 degrees) behind the first one. If you could somehow delay the sound coming from one channel of your stereo, you can broaden the 45-degree line into a full two-dimensional shape. The closer the delay is to 90 degrees out of phase, the more symmetrical the light form will be. Imagine a pure source of sine waves—a sine wave oscillator. The oscillator is sending out waves at a frequency of 100 Hz. It has two output channels called sine and cosine. Both channels are linked so they run at precisely the same frequency, but the cosine channel is delayed 90 degrees. The lightform projected on the screen is now a perfect circle. The circuit in ill. 20-7 provides such a two-channel oscillator. Two controls allow you to change the frequency and “symmetry” of the sine waves. The symmetry (or phase) control counters the destabilizing effects caused by rotating the frequency knob. This circuit, with parts list provided in TABLE 20-2, is designed so that the resistors and capacitors are the same value. Changing the value of one resistor throws off the balance of the circuit, and the symmetry control helps rebalance it. Note that the frequency and symmetry controls provide a great deal of flexibility in the shape of the projected beam. Fiddling with these two potentiometers allows you to create all sorts of different and unusual light forms. ill. 20-6. Two sine waves; the bottom wave is delayed 90 degrees from the top wave. Cosine output Sine output ill. 20-7. One way to implement a sine/cosine audio generator for operating two galvanometers. Table 20-2. Sine/Cosine Generator Parts List
The circuit's designed around the commonly available 747 dual op amp (two LM741 op amps in one package). You can use almost any other dual op amp, such as the LM1458 or LF353, but test the circuit first on a breadboard. For best results, use a dual op amp. You can obtain even more outlandish light forms when combining the sine and cosine signals from two separate oscillator circuits. On a perf-board, combine two oscillators using two LM741 op amps. An overall circuit design is shown in ill. 20-8. One set of switches allows you to turn either oscillator on and off and the input controls let you individually control the amplitude from each sine/cosine channel (for a total of four inputs). A parts list for the general circuit's in TABLE 20-3. The switch lets you flip between mixing the sine inputs together or criss-crossing them so that the sine channel of one oscillator is mixed with the cosine of the other oscillator, and vice versa. * When the switch is in the “pure” position(A)—sine with sine and cosine with cosine—you obtain rounded-shape designs, such as spirals, circles, and concentric circles. * When the switch is in the “cross-cross” position (B)—sine with cosine for both channels—you obtain pointed shapes, like diagonals, stars, and squares. Like the drive circuit, you should place the oscillator, with all its various potentiometers, in a project box or tuck it inside a console. Provide two ½-inch jacks for the outputs for the two galvos. Table 20-3. Complete Light Show Circuit Parts List
All resistors are 5 to 10 percent tolerance, ¼-watt. ill. 20-8. A schematic for designing a two-channel sine/cosine audio generator, with dual op-amp mixers (note: use separate op amps for the mixers). Using the Oscillator Connect the outputs of the oscillator to the inputs of the drive circuit. Apply power to both circuits and rotate the mixer input controls (R1, R2, R6, and R7) to their fully on positions. Flick on switch #1 so that only the signals from one oscillator are routed to the mixer amps and turn switch #3 to “A” position. Slowly turn the control knobs until the galvanometers respond. If the galvanometers don’t seem to respond, temporarily disconnect the jumpers leading between the oscillator and drive circuits and plug an amplifier into one of the oscillator output channels. You should hear a buzzing or whining noise as you rotate the frequency and symmetry controls. If you don’t hear a noise, double-check your wiring and be sure the mixer controls are turned up. When turned down, no signals can pass through the mixing amps. Aim a laser at the mirrors and watch the shapes on a nearby wall or screen. Get the feeling of the controls by turning each one and noting the results. With the symmetry control turned down and the frequency control almost all the way down, you should see a fairly round circle on the screen. If the circle looks like an egg, adjust the mixer controls to decrease the X or Y dimension, as shown in ill. 20-9. If the egg is canted on a diagonal, the phase of the cosine channel isn't precisely 90 degrees. Try adjusting the symmetry control and fine tuning it with the frequency control. There should be one or more points where you achieve proper phase between the sine and cosine channels. ill. 20-9. The basic circle produced by turning on one sine/cosine generator and adjusting the frequency and symmetry controls to produce a pure sine wave. Now turn off the first oscillator and repeat the testing procedures for the second oscillator. It might behave slightly different than the first due to the tolerance of the components. If you need more precise control over the two oscillators, use 1-percent tolerance resistors and High-Q capacitors. For really interesting light forms, turn on both oscillators and adjust the controls to produce various symmetrical and asymmetrical shapes. At many settings, the light forms undulate and constantly change. At other settings, the shape remains stationary and can appear almost three-dimensional. FIGURES 20-10 and 20-11 show sample light forms created with the circuit and galvanometers described above. Alternate between “A” “B” settings by flicking switch #3. Note the different effects you create when the switch is in either position. Powering the Oscillator and Drive Circuits So far we’ve discussed using galvo oscillator and drive circuits but have paid no attention to the power supply requirements. Although you can build your own dual-polarity power supply to run the galvo system, I strongly recommend that you use a well-made commercial supply, one that has very good filtering. Sixty cycle hum, caused by insufficient filtering and poor regulation, can creep into the op amps and make the galvos shudder continuously. Output voltage and current depend on the galvanometers you use. I successfully used two General Scanning GVM 734 galvos with a power supply that delivered volts at about 250 mA for each polarity. You might need a more powerful power supply if you use different galvanometers (some require ± 12 at 1 amp or more). The power supply I used for the prototype system was surplus from a Coleco computer system that cost $20.95. Look around and you can find an equally good deal. ill. 20-10. One of many spiral light forms created by turning on both sine/cosine generators. ill. 20-11. A clearly definable “Lissajous” figure, made with the galvanometer light show device. Useful Modifications and Suggestions Not shown in the driver circuit above is an additional switch that allows you to change the polarity to one of the galvanometers. This provides added flexibility over the shape of the light forms. Wire the switch as shown in ill. 20-12. The drive circuit detailed above might not provide adequate power for all galvanometers. If the galvos you use just don’t seem to be operating up to par, use the drive circuit shown in ill.20-13, developed by light show producer Jeff Korman (see parts list in TABLE 20-4). This new driver is similar to the old one but provides better performance at low frequencies. Korman also uses a special-purpose sine/cosine oscillator chip made by Burr-Brown. The chip, called the 4423, is available directly from Burr-Brown or from Fobtron Components. ill. 20-12. Wire a DPDT switch to From one of the galvanometers to reverse its direction in relation to the other galvanometer. Cost is high ($35 to $55) but it provides extremely precise control over frequency with out the worry of knocking the signals out of 90-degree phase. Other useful tips: * Whenever possible, try to reduce the size of the light forms; it makes them appear brighter. * Connect an audio signal into one channel of the drive circuit and connect the sine/cosine oscillator into the other channel. The light form will be modulated in 2-D to the beat of the music. * You can record a galvanometer light show performance by piping the output of the oscillators into two tracks of a four- track tape deck. Use the remaining two tracks to record the music. When played back, the galvanometers will exactly repeat your original recording session. This is how most professional light show producers do it. Notes: Q1 and Q2 must be on heatsinks’ Use supply voltage to complement galvanometer; up to ± 18 Vdc. ill. 20-13. An enhanced high current galvanometer circuit designed by light show consultant Jeff Korman. Table 20-4. Enhanced Galvanometer Driver Parts List
All resistors are 5 to 10 percent tolerance, ¼ watt, unless otherwise indicated. * Try adding one or two additional oscillators. Combine them into the mixing network by adding a 10k pot (for volume control) and a 10k input resistor. Wire in parallel as shown in the ill. 20-8 schematic, above. * Triangle or sawtooth (ramp) waves create unusual pointed-star shapes, boxes, and spirals. You can build triangle and sawtooth generators using op amps, but an easy approach is to use the Intersil 8038 or Exar XR-2206 function generator ICs. Making Your Own Galvos A set of commercially-made galvanometers can set you back $150 to $280, even when they are purchased on the surplus market. If you are interested in experimenting with laser graphics and geometric designs but are not interested in spending a lot of money, you can make your own using small dc motors. Follow the diagram shown in ill. 20-14 to make your own galvanometers. You can use most any 1.5- to 6-volt dc motor, but it should be fairly good quality. Test the motor by turning the shaft with your fingers. The rotation should be smooth, not jumpy. Measure the diameter of the outside casing. It should be about 1 inch. Refer to TABLE 20-5 for a list of required parts. Use a high-wattage soldering iron or small brazing torch to solder a penny onto the side of the motor shaft. For best results, clean the penny and coat it and the motor shaft with solder flux. Make sure the penny is thoroughly heated before applying solder or the solder may not stick. You’ll need to devise some sort of clamp to hold the penny and motor while soldering—you need both hands free to hold the solder and gun. Let the work cool completely, then mount a small ½-by-¾-inch front-surface mirror to the front of the penny. You can use most any glue: Duco adhesive or gap-filling cyanoacrylate glue are good choices. Note that the mirror shouldn't be exceptionally thick. You get the best results when the mirror is thin—the motor has less mass to move, so it can vibrate faster. Snap the motor into a ¾-inch electrical conduit clamp and fit it into position (the clamp will have a 1-inch opening and will hold most small hobby motors). If the clamp is too small, widen the opening by gently prying it apart with a pair of pliers. Mount the motor and clamp to a 2-by-3-inch acrylic plastic base (½-inch thickness is fine). Drill holes as shown in ill. 20-15. Use a 6/32 by ½-inch bolt and a 6/32 nut to secure the pipe clamp to the base. Use a treated, synthetic sponge and cut into two 1-by-½-inch pieces. The sponge should be soft but will dry out when left overnight. After the sponge has dried out, compress it and secure it under the penny using all-purpose adhesive. Now slide a 1-by- ½-inch piece of anti-static foam into the gap between the sponge and penny. The fit should be close but not overly tight. If you need more clearance, compress the sponge by squeezing it some more. The finished dc motor galvanometer is shown in ill. 20-16. As an alternative, cut a piece of ½-inch foam and stick it under the penny. Try different foams to test their “suppleness.” The foam should be soft enough to let the penny and mirror vibrate but not so soft that it acts as a tight spring and bounces the penny back after only a small movement. Using the Motor/Galvanometers Attach leads to the motor terminals and connect the homemade galvanometers to the drive circuit and oscillator detailed earlier in this section. Repeat the testing procedures outlined for commercially made galvos. Position the motors so that they are 90 degrees off-axis and shine a laser onto both mirrors. You should see shapes and patterns as you adjust the controls on the oscillator. ill. 20-14. Basic arrangement for making galvanometers using small dc motors. The sponge prevents the mirror and shaft from turning more than 20-25 degrees in either direction and helps dampen the vibrations. Table 20-5. Dc Motor Galvanometer Parts List
ill. 20-15. Cutting and drilling template for the base for the homemade motor galvanometers. ill. 20-16. A completed motor galvanometer, secured to the base with a ¾-inch electrical conduit clamp. The motor/galvanometers can be mounted in a variety of ways. One approach is to use metal strips bent 90-degrees at the bottom. Drill matching holes in the strip and attach the base of the motor/galvos to the strips using 6/32 hardware. You can also secure the base of each motor/galvanometer using ½-inch galvanized hardware brackets (available at the hardware store). The light forms might not be perfectly symmetrical. Depending on the motors you used and the type and thickness of foam backing you installed, one motor might vibrate at a wider arc than the other. Try adjusting the foam and sponge on both motors to make them vibrate the same amount. SMOKE EFFECTS Smoke effects are obtained by spreading the laser beam into an arc (the light is projected as a straight line) and filling the room with smoke or vapor. Because you see only a thin slice of the smoke through the arc of laser light, you can clearly view the air currents as they swirl and shift. Smoke effects in professional light shows require multi-watt lasers—a 2- to 5-watt argon laser makes wonderful smoke effects. The “smoke” is often vapor left by heating dry ice. Dry ice vapor is heavier than air so it must be blown through the stream of laser light. Small blowers keep the air circulating. You can experiment with laser smoke effects by using a helium-neon laser (1 mW or more). Although the smoke isn't visible at any distance, it can be used for small, amateur light shows. You can also use laser smoke effects to view fluid aerodynamics (see Section 22) or just to see what happens to smoke particles in a ventilated room. You can use dry ice vapor (buy the dry ice from a local ice-packing company), smoke from a cigarette, incense stick, or match. In all cases, exercise reasonable care. Dry ice can cause frostbite, so handle it only with gloves and place it in Pyrex or metal containers (plastic and regular glass could shatter). Cigarettes, incense, and matches present a fire hazard. Get help if you are not sure of what you are doing. Note that smoke—and all particles in the air—are seen when laser light shines through them. You see them best when you are on one side of the smoke particles and the laser is on the other. You see the outline of the smoke particles as they swirl around. Casting the Arc Spread the laser beam into an arc using the sheet effects described in the last section. As a recap, you can spread light out in an arc by: * Spinning a mirror on the side of a motor shaft. * Rotating an off-axis mirror mounted on the end of a motor shaft. * Spinning a holograph scanner mirror wheel. * Spreading the light with a cylindrical lens. These approaches don't allow you to change the spread of the arc. You can obtain more control over the angle—make it narrow or wide—by using a single galvanometer (commercially made or homemade) and by adjusting the amplitude of the drive signal. You can use the oscillator and driver circuits detailed previously in this section. Making the Smoke Effect Turn off all the lights except for a dim pilot light that you can extinguish remotely. Light the cigarette, incense, or match, and waft the smoke under the laser light arc. Alternatively, dunk the dry ice in a pail of tepid water. Move to a position that allows you to clearly see the smoke and turn off the pilot light. Depending on the spread of the arc, the power of the laser, and the amount of smoke or vapor, you should clearly see particles swirling in the air. Watch the effect as you add more smoke or vapor or make the spread of the arc smaller. If the air is moving too fast, the smoke/vapor might disperse too quickly. Turn off blowers, air conditioners, and other appliances that may be agitating the air. On the other hand, if the room gets too filled with smoke, you’ll see a general haze in the light and the swirling won’t be as easy to see. Clear the room by airing it out. Use blowers or fans to speed up the process. USING ARGON AND KRYPTON LASERS Most professional laser light shows use argon or krypton lasers. Both of these are manufactured in high-output versions and provide two or more colors. As you learned in earlier sections, argon lasers emit light at two principle wavelengths or mainlines—488.O nm and 514.5 nm. Krypton lasers have the unique ability to produce light at just about any wavelength, providing a spectrum of colors. Because they can produce all three primary colors—red, green, and blue—krypton lasers are often used in color holography. The three primary colors can also be created by using an argon and helium-neon laser. Using a prism or set of dichroic filters allows you to separate the mainlines. The prism disperses the light into its component colors so that each color can be individually manipulated. Dichroic filters let you block all but the color you want. E.g., a “red” filter placed in front of an argon laser will block the green 514.5 nm mainline. Serious light-show applications require a laser with a minimum power output of 100 mW. Better, more dramatic results are obtained with even higher wattages; it’s not uncommon to see 3- to 5-watt argon lasers used in professional light shows. These Class N devices are downright dangerous unless you know precisely what you are doing. They also require water cooling and extensive plumbing, making them a hassle to use. High-output krypton and argon lasers are unreasonably expensive but if you are serious about laser light shows, you might locate a used specimen at an affordable price ($5,500 or so). If you keep an eye out and make plenty of contacts, you might luck onto a high-output industrial-grade argon laser—used for such applications as medicine, optical disc manufacturing, and forensics—that is no longer functioning but is repairable. Per haps the tube is gassed out or maybe the power supply is fried, but the cost of fixing the laser will be less than buying a new one. Before you sign the check, make sure you know what the problem is and that you are confident the laser can be fixed. High-output lasers can’t be plugged into the ac socket and aimed at the wall. Most require 220-volt, three-phase ac (wall outlets provide 110-volt single-phase ac). The la ser generates too much heat for air cooling and must be shrouded by water to keep it cool. The water supply must be continually circulating from the faucet to a drain. Adequate filtration and pressure regulation is needed to prevent deposits in the cooling jacket or rupturing the tube. Finally, but most importantly, the power supplies used to operate high-output lasers produce high current at high voltage. Touching a high-voltage component or wire on the power supply or tube will kill you—no exceptions. Thoroughly familiarize yourself with the safe operation of the laser before using it. YOU AND UNCLE SAM They say the government has its fingers in everything, and lasers are no exception. Uncle Sam’s interest in lasers is purely one of safety—the federal government wants you to comply with minimum safety requirements before you put on a light show. As you learned in Section 2, “Working With Lasers,” the branch of the government that regulates the laser industry is the Center for Radiological Health, or CDRH (formerly BRH, or Bureau of Radiological Health). The CDRH monitors the manufacture and use of lasers so that harmful laser radiation does not befall unsuspecting people. Most of the CDRH regulations concern the manufacture of lasers, but some sections deal with the use of lasers in public arenas, including light shows. Briefly stated, anyone wishing to conduct a laser light show for public viewing or otherwise demonstrate the operation of lasers to the public, must fill out forms and submit them to the CDRH. These forms provide necessary information on the type and class of laser and how you intend to use it. You must also provide details, as precisely as possible, of how the light show equipment will be arranged, where beam stops will be placed, and the number and type of fail-safe mechanisms used. You must also demonstrate an understanding of the regulations and that you intend to comply with them. In the case of a traveling light show, you must indicate how your laser system can adapt to different rooms and auditoriums. The complete CDRH requirements for laser light shows is too involved to repeat here. You can obtain compliance regulations and application forms directly from the CDRH; their address is given in Section A. GOING PROFESSIONAL Laser light shows can be both fun and rewarding, both on a personal and financial level. Although permanent laser shows, most notably Laserium, are the most visible, they represent only a small number of light shows conducted in the U.S. Many rock bands like to play to the accompaniment of a light show, especially one that includes lasers. Contact local bands and clubs and ask if they would add a laser show to their gig A local non-laser light show producer who has not had the time, inclination, or background to include lasers in his repertoire, might be delighted to have you as a consultant. If you can’t find music groups or nearby light show producers, ask at the radio stations in town (call or drop by). You will probably need to start small and work your way to the big time, all the while adding to your laser system. On a smaller scale are light shows for schools and organizations. What boys’ or girls’ club wouldn’t like to be treated to a light show? These gigs are mostly non-paying, but they are an excellent way to hone your light show talents. Even if you don’t take your light show on the road and perform before a live audience, you can doodle with the art-forms created by the assortment of mirrors, motors, servos, galvanometers, and other sundry equipment on film or videotape. A telecine adapter, used primarily for converting Super-8 movies and 35 mm transparencies to videotape, can be used to capture the light-show images on film. Simply replace the film projector with the laser projector. You can use a video camera or still camera to capture the images on the rear-projection plate. Another alternative is to aim the laser at the wall or screen and photograph or videotape the images directly. This method doesn’t yield the best results, because you pick up the pattern on the wall or screen and the images aren’t generally as brilliant. To photograph the light show art forms, place the camera (video or film) on a tripod and focus the lens on the front of the screen. You might need to use the zoom or macro feature of the lens, or else attach supplementary positive diopter lenses in front of the camera in order to take sharp pictures. Persistence of vision is the capacity of the eye to blend a series of still pictures into smooth motion. A movie is made up of thousands of individual still pictures. These pictures are flashed on the screen faster than our eyes can detect, so the image appears to be in motion. The same technique is used in laser light shows. The scanning of motors, R/C servos, or galvanometers produces a two-dimensional shape on the screen. What appears as a spiral or circle is actually one beam of light, moving so fast that our eyes (and brain) synthesize it into a complete, moving picture. While your eye smooths the scanning of the laser beam to create the illusion of motion, the eye of the camera may be faster, so the results you see on film might not match those you see in person. When taking still pictures of a laser image, choose a shutter speed ‘/15th of a second or longer. Shorter (higher in number) shutter speeds might result in only partial images. Television pictures are also created by flashing a series of still pictures on the screen. The video frame rate for a complete picture is V3o of a second. That’s faster than your eye can detect, so you don’t witness any flicker. Videotaping a laser light show image could result in objectionable flicker. You can see the flicker on your TV set while recording. However, you can often minimize the flicker by adjusting the speed or frequency knob on the light-show motor/galvanometer controller. |
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