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AMAZON multi-meters discounts AMAZON oscilloscope discounts Even before the laser was invented, science fiction writers told of incredible weapons and machines that emitted a bright saber of light, a death ray that disintegrated everything in its path. In the 1951 classic The Day the Earth Stood Still, a 7-foot tall “police robot” was equipped with a powerful disinto-ray gun. The gun was mounted behind a visor in the robot’s helmet and shot its high-intensity, pencil-thin flame with great precision. Even today, science fiction movies and books place high emphasis on weapons that use light instead of bullets. But real science hasn’t kept up with science fiction; most lasers do little or no harm to human flesh, and many can’t cut through a piece of paper, let alone tanks, automobiles, and spaceships. As unlikely as practical laser-based weapons seem given the current limitations of the state-of-the-art, it’s possible that weapons using an intense form of light could someday be developed. In 1983, President Ronald Reagan outlined a plan for outfitting land- and space-born satellites with laser weapons as a defensive measure against ballistic missiles. What are the possibilities of developing powerful laser weapons that thwart nuclear destruction? Can weapons be placed on the ground, installed in tanks or towed on trailers? And what about non-war use of laser guns: could they be used—as they are in the “Star Trek” TV show and movies—to either kill or stun an opponent? Let’s take a brief look at laser weapons and the technology that’s currently available. Then read the plans for constructing a useful but relatively harmless laser “gun” using a helium-neon tube. The emphasis of the laser gun is to show you what goes into hand held lightwave weapons, not to make an effective munition. On a more practical standpoint, laser pistols and rifles provide a means for target practice without wasting bullets, pellets, or B-B’s and with much less risk of bodily injury. AN OVERVIEW OF LAND/SPACE LASER WEAPONS Lasers are already used in the battlefield, but not as offensive weapons. The U.S. Army and North Atlantic Treaty Organization (NATO) use laser rangefinders for determining the distance between the firing line and the target. The laser system can be mounted on a rifle stock and carried by one person. A number of high-caliber cannon, tanks, and helicopters use their own laser rangefinders, controlled by an on-board firing computer. Laser rangefinders operate in a variety of ways, but many work by means of transmitting short modulated pulses, then waiting for an echo. The timing of the return signal indicates distance. Accuracy is within 10 to 20 feet for most systems and range is up to 7 miles. Reagan’s Strategic Defense Initiative (SDI), which he announced in a widely publicized speech on March 23, 1983, calls for the deployment of land- and space-based weapons using one or all of three possible technologies: * Particle beam weapons, shooting atoms of neutral or charged particles from ground- or space-based platforms. * Kinetic energy weapons, from ground-based cannon, that fling high-speed projectiles at the target. * Laser weapons, which use short-wavelength electromagnetic energy to heat up the target, damaging its electronics or flight control mechanism. Of the three types, kinetic energy weapons ( KEW) have received the greatest attention. Battlefield KEWs are believed to be technologically possible, and may provide the greatest amount of firepower. The most common variety of KEW is the electromagnetic rail-gun, which shoots specially designed heavy metal “bullets” at about six miles per second (the bullet from an M-16 rifle travels at about 2/3 of a mile per second). Rail-guns require a great deal of energy and many designs are one-shot affairs: the gun is severely damaged after just one firing. To be effective, the wavelength of a laser weapon must be short, at least in the visible band but preferably in the ultraviolet or x-ray band. The greatest difficulty in designing short-wavelength lasers is power—the shorter the wavelength, the more energy that's required. Optical (visible or ultraviolet) lasers work by heating the skin of the target. The beam must remain at the same spot for several seconds until the skin is hot enough to do internal damage to the target. This is tough because the typical ballistic missile travels in excess of 6 miles per second. Imagine focusing on the same 2- or 3-foot spot over a distance of 50,000 feet and you have an idea how accurate such a laser weapon must be. In addition to the problems of accuracy, laser weapons of any power tend to be monstrous. That limits them to ground-based ray guns, using mirrors to direct the beam to the target. High-powered lasers using turbine-powered chemical jets have been developed and even placed aboard aircraft, but the wavelength of the light is long—6 to 10 micrometers—far in the infrared region. This makes the laser relatively inefficient at destroying their targets. X-ray lasers, still in the “so secret they don’t exist” category, emit an extremely high powered beam that can literally destroy a missile in mid-flight. X-rays can’t be deflected by mirrors, however, which means that the weapon must be easily aimed and in a direct line of sight to the target. Fortunately, x-ray lasers can be built small, experts say, making them suitable for space-based operation. The biggest disadvantage to x-ray lasers is that they use an internal atomic explosion to work, so they are essentially one- shot devices. A relative newcomer to the SDI (or “Star Wars”) scene is the free-electron laser, which is being developed at several national laboratories and universities. The free- electron laser uses a stream of electrons that's made to emit photons of light after being oscillated by giant electromagnets. Free-electron lasers (FELs) have been built and they do work. But if put into production, an actual anti-ballistic missile FEL would take up a football field or more. Obviously, such a device would be useful only as a stationary ground-based weapon. It’s possible, though unlikely, that it would be built over a span of several years on a low-orbiting space platform. SMALL-SCALE WEAPONS USING LAB-TYPE LASERS So far, we’ve discussed high-power laser weapons designed to counter a nuclear attack. Laser guns in the movies are often hand-held devices, or at most, small enough to prop on a vehicle. Lasers powerful enough to inflict damage but small enough to be carried have been developed, but they are not used in any current military application. It’s relatively easy, for example, to build a hand-held ruby laser that puts out bursts of large amounts of light energy. When focused to a point, the light from a ruby laser can cut through paper, cloth, skin, or even thin metal. Ruby crystals are poor conductors of heat, so ruby lasers emit only short pulses of light to allow the crystal to cool between firings. Nd:YAG lasers operate in a similar fashion as ruby lasers but can produce a continuous beam. Making a hand-held Nd:YAG laser is no easy feat, however. The Nd:YAG crystal must be optically pumped by another high-powered laser or by an extremely bright flash lamp or light source. Though the power output of an Nd:YAG laser is extremely high, considering the current state-of- the-art, a hand-held model is impractical. However, such a weapon could be built as a “laser cannon,” transported on an armored vehicle or on a towed trailer. CO lasers are often used in industry as cutting tools. This type of laser is known for its efficiency—30 percent or more compared to the 1 to 2 percent of most gas and crystal lasers. A pistol-sized CO laser would probably be difficult to design and manufacture because the CO gas mixture (which includes helium and nitrogen) must be constantly circulated through the tube. What’s more, the laser requires a hefty electrical power supply. Still, such a weapon could be built in an enclosure about the same size as a personal rocket launcher. These are designed to be slung over a shoulder and fired when standing in an upright position. BUILD YOUR OWN HELIUM-NEON LASER PISTOL The small lab-type laser weapons described above would cost several thousand dollars to build and require expert machining and tooling. You can readily build your own low power, hand-held laser using a commonly available and affordable helium-neon tube and 12-volt dc power supply. The pistol is made from 2- and 1¼-inch schedule PVC plumbing pipe that you can cut with an ordinary hack saw. Defining Barrel Length The exact length of the pistol barrel depends on the laser tube and power supply you use. The laser used in the prototype pistol is a common variety 2 mW tube measuring 1½ inches in diameter by 7½ inches. You can obtain even smaller tubes through some laser dealers and make your pistol more compact. The power supply is one of the smallest commercially made, measuring a scant 7/8-inch in diameter by slightly under 4 inches in length. This particular power supply was purchased through Meredith Instruments but is also available from Melles Griot and several laser manufacturers. Cutting the Barrel and Grip TABLE 21-1 provides a parts list for the laser pistol. Assuming you use the same or similar tube and power supply, cut a piece of 2-inch schedule 40 Pvc to 12½ inches. Sand or file the cut ends to make them smooth. Drill a ¾-inch diameter hole four inches from one end of the tube, as shown in ill. 21-1. This hole serves as the leadway for the power wires. Next, cut a length of 1¼-inch schedule 40 PVC to 6¼ inches. Using a wide, round file, shape one end of this piece so that its contour matches the 2-inch PVC. The angle of the smaller length of pipe, which serves as the grip, should be approximately 10 to 15 degrees. The match between the barrel and grip does not need to be exact, but avoid big gaps. Cut the grip a little long so to allow yourself extra room for shaping the contour. The grip is about the right length if it measures 6 inches top to bottom. Cut a ¼-inch hole 1¼ inches from the bottom of the grip and another ¼-inch hole 90 degrees to the right but at a distance of 4¾ inches from the bottom (see ill. 21-2). The lower hole is for the ¼-inch phone jack for the power, and the upper hole is for the push button switch. Note that the size of the upper hole depends on the particular switch you use. The switch detailed in the parts list is commonly available at Radio Shack and other electronics outlets. If you use another switch, you should measure the diameter of the shaft and drill a hole accordingly. Cut two ¼-inch-wide slits approximately ½ inch from the top of the grip. The slits should be opposite one another and at right angles to the top hole (used for the switch). Unthread the loose end of a 12-inch-long (3½-inch diameter) hose clamp through the slits. Tighten the clamp one or two turns, but not so much that you can’t insert the barrel into it. The pistol so far should look like ill. 21-3. Table 21-1. Laser Pistol Parts List
ill. 21-2. Cutting and drilling guide for the He-Ne laser pistol grip. Wiring the Jack and Switch Use 20- or 22-gauge stranded wire to connect the components as shown in ill. 21-4. The wire lengths are approximate and provide some room for easily fitting the jack, switch, power supply, and tube into the PVC enclosure. After you have soldered the jack and switch, mount them in the grip, feed the wires through the hole in the barrel, and mount the grip to the barrel. Center the hole in the grip and tighten the clamp. ill. 21-1. Cutting and drilling guide for the He-Ne laser pistol barrel. ill. 21-3. Barrel and grip held in place with an adjustable car radiator hose clamp. ill. 21-4. Wire the He-Ne laser pistol as shown in this diagram. Be aware of the high voltages present at the output of the power supply. Mounting the Laser Tube and Power Supply Attach the power supply leads to the tube. With the power supply and tube used, the anode lead from the supply connects directly to the anode terminal of the tube. This wire must be kept short to minimize current loss and high-voltage arcing. The cathode lead stretches from the supply to the opposite end of the tube. This design works well because the tube emits light from the cathode side, opposite the power supply. Because not all He-Ne lasers operate this way, you’ll want to choose the tube carefully. The tube must emit its light from the cathode side or the power supply will get in the way. Loosely attach the power supply to the tube by wrapping them together with electrical tape. The tube should be protected against shock by wrapping it in a thin Styrofoam sheet, the kind used for shipping fragile objects. One or two wraps should be sufficient. Close up the sheet with electrical tape. Final Electrical Connection and Assembly Solder the wires from the jack and switch to the power supply. Be sure to observe proper polarity. Slide the tube and power supply into the barrel so that the output end of the laser faces forward. Drill a ¾-inch hole in the approximate center of a 2-inch knockout “test” plug (available in the ABS plumbing pipe department of most hardware stores). Because the tube might not rest in the exact center of the barrel, determine the proper spot for drilling by first inserting the plug and observing the location of the output mirror. Mark the spot with a pencil, remove the plug, and drill out the hole. After drilling, replace the plug and push the tube into the barrel so that the output window is just flush with the inside of the plug. Don’t allow the window to protrude outside the plug, or you run a greater risk of chipping or breaking the output mirror. Insert another 2-inch plug in the rear of the barrel. Test plugs are not routinely available for 1¼-inch pipe, so you must use an ordinary end cap for the bottom of the grip. Slip the end cap over the pipe; the fit should be tight. If not, try another end cap. Building the Battery Pack The battery pack for the laser is separate, not only because it allows you to build a smaller gun but allows you to power the device from a variety of sources. The main battery pack consists of two 6-volt 8 AH lead-acid batteries contained in a 4¾-by-7¾-by-2¾-inch phenolic or plastic experimenter’s box (available at Radio Shack). The batteries are held in place inside the box with heavy double-sided foam tape. The battery pack contains a fuse and power jack, mounted as shown in ill. 21-5. A parts list for the pack is provided in TABLE 21-2. The fuse is absolutely necessary in case of a direct short. Lead-acid batteries of this capacity produce heavy amounts of current that can easily burn through wires and cause a fire. A 5-amp fast-acting bus fuse provides adequate short-circuit protection with out burning out during the short-term shorts that can occur when plugging in the battery pack cable. Wire the battery pack as indicated in ill. 21-6. When wired in series, the two 6-volt batteries produce 12 volts. The high capacity of the batteries means you can operate the laser for at least an hour before needing a recharge. I have operated the prototype pistol for up to 6 hours before needing a recharge. ill. 21-5. The internal arrangement of the twin six volt batteries, fuse, and power jack for the battery pack. Table 21-2. Battery Pack Parts List
To make the battery pack conveniently portable, insert two 5 eyelet screws near the top of the box. Snap on a wide camera strap and adjust the strap for your shoulder. You can sling the battery pack over your shoulder while holding the pistol in your hands. Current is delivered from the battery pack to the pistol by means of a 6- to 12-foot coiled guitar extension cord. These are available at Radio Shack and most music stores. Buy the two-wire mono variety; you don’t need the three-wire stereo type. Remember to double-check the hookup of the power jacks in the battery pack and pistol. Make sure that the positive terminal connects to the tip of the jack. Battery Recharger The battery recharger is a surplus battery eliminator/charger pack designed for 12-volt systems. The pack outputs 13 to 18 volts at about 350 mA. The batteries can be recharged in the box by unplugging the power cord that stretches between the pack and pistol and plugging in the recharger. At 350 mA, recharging takes from 10 to 14 hours. Because the battery eliminator/recharger isn't “intelligent,” be sure to remove it after the recharge period. Otherwise the batteries could be damaged by overcharging. ADDING ON TO THE LASER PISTOL There are several modifications you can make to the laser pistol to increase its functionality and versatility. These include a power indicator, modulation bypass jack, and single-shot circuit. Power Light Add-on A power light provides a visual indication that the laser gun is on. The light is especially helpful if you are using the pistol in daylight when the beam is hard to see and you want to be sure that the gun is working. ill. 21-6. The wiring diagram for the battery pack. Don't omit the fuse. The power light consists of a light-emitting diode and current-limiting resistor. Drill a hole for the LED in the rear test plug and mount it using all-purpose glue. The LED is connected in parallel with the laser power supply: when you pull the switch, current is delivered to the power supply and LED. Modulation Bypass Add-on The modulation bypass permits you to easily modulate the beam with an analog or digital signal. The bypass consists of a ¼-inch miniature earphone jack connected between the cathode lead of the power supply and the cathode terminal of the tube. Both LED and modulation bypass add-ons are shown in ill. 21-7. To add the bypass to the pistol, drill a hole for the jack in the rear test plug. Apply high-voltage putty around the terminals to the jack; be sure that none of the putty interferes with the contacts of the jack. The putty helps prevent arcing due to high voltages. When not using the bypass jack, insert a shorting plug into the jack (the shorting plug has its internal contacts shorted together). To use the modulation bypass, remove the shorting plug and insert the leads from a modulation transformer, as detailed in Section 13, “Free-Air Laser Light Communications.” The transformer can be driven by an audio amplifier so signals can be transmitted via the laser beam. Depending on what you connect to the modulation transformer, you can transmit audio signals or digital data over distances exceeding 1 mile. Aiming Sights or Scope If you plan on using the pistol for target practice, you’ll want to add front and rear sights along the top of the barrel. Because the beam comes out of the barrel almost 1¼ inches from the top, you are bound to experience parallax problems with any type of sight system you use. For best results, mount the sights as close the barrel as possible—the further away they are from the barrel, the more pronounced are the effects of parallax error. ill. 21-7. Schematic diagram for adding the modulation bypass and LED indicator enhancements to the He-Ne laser pistol. Effective homemade sights can be made inserting two small, flat or pan-head ma chine screws into the top of the barrel (use flat-blade screws, not hex or Philips). The screws should be short and shouldn't overly extend inside the barrel. If they do, the tips of the screws could interfere with the laser and power supply. Adjust the leveling of the sights by turning the screws clockwise or counter-clockwise. Position the “slits” of the tops of the screws to that they are parallel to the length of the barrel. By adjusting the height of the screws you compensate for the differences in parallel between the sight and the laser tube. Note that there is no need to adjust for windage because the light isn't affected by the wind, nor do you need to compensate for bullet trajectory, because the light beam will continue in a straight path. Painting Although painting the laser pistol won’t make it work better, it certainly improves its look. Prior to painting, you should remove the end caps, tube, switch, and jack, or else use masking tape to prevent paint from spraying on them. Be particularly wary of paint coming into contact with the output mirror of the tube and the internal contacts of the power plug. Black ABS plastic pipe does not need to be painted, saving you from this extra step. However, straight pieces of 1¼- and 2-inch black ABS plastic is hard to find. Most plumbing and hardware stores carry only pre-formed fittings for drains and other waste-water systems. ill. 21-8. The completed He-Ne laser pistol, with modulation bypass shorting plug installed. Spray on a light coast of flat black paint; Testor’s hobby paints are a good choice, and when used properly, won’t sag during drying. The paint dries to a touch in 10 to 15 minutes, but it'sn’t cured until overnight. You can, of course, paint the pistol any color. A complete, painted pistol is shown in ill. 21-8. APPLICATIONS FOR THE LASER PISTOL Let’s face it, the He-Ne laser pistol isn’t going to make you Luke Skywalker, so there is little chance you’ll be going around the galaxy disintegrating bad guys. The output of the tube used in the pistol (like all other helium-neon lasers) isn’t enough to be felt on skin, it won’t burn holes in anything nor is it capable of any kind of destruction. That leaves rather peaceful applications of the pistol. Before detailing some of the fun you can have with the laser pistol, I need to stress the safety requirements once more. The hand-held nature and design of the pistol might prompt you to use it in a Laser Tag-like game. Don’t. The eyes of you and your opponent (man or beast) could be exposed to the laser beam—a definite health hazard. Point the pistol only at inanimate “blind” objects. Hand-Held Pointer Although the He-Ne pistol is rather large for the task, it can be effectively used as a hand-held pointer. Even in a large auditorium with a brightly lit movie, the laser pointer can be easily seen on the screen. If you don’t care for the pinpoint of light, try shaping the beam with optics and a shape mask. Use a double-concave lens to expand the beam from its nominal 0.75 mm to about 10 millimeters. A bi-convex lens collimates the beam—makes the rays parallel again. In front of the collimating lens you place a mask of an arrow, cut from a piece of thick black plastic, aluminum foil or photographic film (your local offset printer can provide a high-contrast mask of any artwork). When using aluminum foil, paint both front and back sides to cut down light reflections. Because the positioning of the optical components depends on the focal lengths of the lenses, you should experiment with some lenses and try out the system before building it onto the pistol. When you have determined the proper placement of the lens and mask, mount them in PVC pipe or paper tube and attach the pipe to the end of the pistol. A 2-inch coupler can be used to easily attach extensions to the front of the laser. The Ultimate Cat Toy Believe it or not, many owners of helium-neon lasers spend countless hours using the bright red beam as a high-tech cat toy. If you have a cat and it’s fairly playful, try this experiment: When the animal is least expecting it, shine the beam on the floor (not into its eyes). Most cats will react to the beam by pouncing on it. Of course, they can never get it because it’s simply a spot of light on the carpet. Scan the beam at a fairly slow rate and have the cat chase after it. Dogs don’t seem to be much interested in laser beam spots. Mine just licks the end of the laser and wags his tail. |
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