How Lasers Are Going to Work for You (Jul, 1970)
How Lasers Are Going to Work for You
The light fantastic is no longer a scientific curiosity: It’s now being used for just about everything from moon measuring to tire checking
By C. P. GILMORE / PS Consulting Editor, Science
At RCA’s David Sarnoff Laboratory in Princeton, N.J., Dr. Henry Kressel handed to me what appeared to be an odd-looking gold-colored bolt about three quarters of an inch long. The threaded part was ordinary enough. But a small block perhaps a quarter of an inch long and half that thick was built onto one side of its flat head. A wire from the head arched up and connected to the side of the block.
“That’s the laser,” he said, pointing to where the wire joined the block. “This metal block?” I asked.
He took the device, walked into a laboratory next door, put it under a powerful binocular microscope, and peered into the instrument as he adjusted it.
“There,” he said. “Look where the wire joins the block.”
I did. And there was a smaller block, some 10-thousandths of an inch on a side, I learned, sticking to the side of the large block. The wire was connected to one side of the microscopic laser. The large block, I found, was just a heat sinkâ€”a blob of material to soak up heat from the laser.
The device I was looking at is a solid-state injection laserâ€”made primarily of a semiconductor material called gallium arsenideâ€”that is cousin to the transistor. It’s a relatively unknown member of a very famous family. If you still think of lasers as a bunch of laboratory curiosities, you couldn’t be farther off the beam. In the 10 years since the laser was invented, scientists and engineers have been vying with each other to find ever more applications for their laser devices.
Modern use of lasers
Today, lasers are working for you in ways you may have never suspected. For example, they’re . . .
â€¢ Guiding tunnel and trench diggers
â€¢ Welding microcircuits
â€¢ Drilling holes in rubber nipples for baby bottles
â€¢ Spotting tire defects
â€¢ Machining parts to ultra-fine tolerances
â€¢ Helping predict earthquakes.
How lasers work
The lasers that perform these and other tasks are an odd breed of exotic lightmaker. Normal lasers work when energy of some kind “pumps” their active atoms or molecules to “excited” or higher-than-normal energy states. When they cascade back down to normal, they release laser light. In other words, you pump energy in, it gushes back out in the form of laser, beams.
The pumping had always been done with either light or electricity. Several years ago, researchers in several places began looking for a chemical reaction that could pack energy into the atoms and make them laseâ€”give off laser lightâ€”without using any electrical energy. Projects at Aerospace Corporation, Avco, and Cornell University eventually produced such lasers. When the right chemicals are pumped in, they begin to react with each other and generate laser light.
Now, United Aircraft scientists have apparently gone a step further. They’ve built a CO2 laser that can draw tremendous amounts of energy from certain chemical reactions. Just how this has been done is secret. But researchers say it might be done several ways. For example, the exhaust of a jet engine or even of a Saturn 5 F-l rocket engine might be pumped directly into the laser chamber. Under the right conditions, this exhaust could contain highly excited carbon dioxide, carbon monoxide, and water-vapor molecules, which could be made to react and generate extremely powerful beams of laser light.
The laser is developing into one of the most versatile devices of the age because it produces an entirely new kind of light; one never before seen by human eyes. Regular light is incoherentâ€”a jumble of colors and frequencies all out of step, like a mob stomping out a grass fire. But the laser’s educated ray is coherentâ€”composed of light waves of just one frequency (color), all in perfect step, like a well-trained ballet corps.
The laser first appeared as a glint in the eyes of physicists Charles Townes and Arthur Schawlow. In 1958 they wrote a paper saying that it should be possible to build a device in which photons, individual packages of light, could be used to stimulate excited molecules to give off yet more photons in step with the original ones. In 1960, physicist Theodore Maiman, then of Hughes, built one. Despite the high-powered physics that led up to its design, it was a deceptively simple deviceâ€”a rectangular chunk of ruby surrounded by a bright photo-flash lamp. Every time the lamp flashed, its photons jiggled certain atoms in the ruby, causing them to give off photons and stimulate yet other atoms to radiate, just the way Schawlow and Townes said it would happen.
The new device was called a LASERâ€”which stood for Light Amplification by Simulated Emission of Radiation. Since then, other investigators have made hundreds of liquids, solids, and gases lase, giving off hundreds of different wavelengths or colors of visible light, and hundreds of other wavelengths of invisible infrared and ultraviolet. Some generate power continuously, others in bursts or pulses.
Because laser light is coherent, it can be focused to an extremely small spot. The energy density of such a spot can be a billion watts per square centimeter or moreâ€”enough to vaporize any substance in existence.
Because the process is so fast, laser light can perform seemingly magical tricks, such as burning the black lettering off an inflated rubber balloon without bursting the balloon.
A laser beam is intensely colli-mated; it spreads very little as it propagates in space. The ray of a simple helium-neon laser will spread into a beam no more than two and a half feet in diameter a mile from the source. By putting it through a telescope backwards, the beam spread can be held to about one-third of an inch per mile.
Finally, the coherence of laser light makes it a superb measuring tool.
A few years ago, the Western Electric Company, which makes most of the telephones in the country, had a problem. The firm makes 30-million miles of hair-fine copper wire a year by drawing copper rods through ever-smaller holes in diamond dies. The process wears out a lot of diamonds, and drilling them is a tedious task. To do it, a technician had to coat a fine steel pin with olive oil and diamond dust and begin to drill. Using many pins and much dust, he would take two days to drill a hole through the world’s hardest substance. In 1966, Western Electric bought a laser, focused it to an extremely fine beam, and began zapping diamonds. Now it takes only a few minutes to blast the hair-like hole all the way through.
A far different process: One manufacturer now uses a laser to punch precisely sized, tapered feed and vent holes in the rubber nipples for baby bottles.
Lasers also make great welders. In welding microcircuits, thousands of circuits are built into one piece of semiconductor the size of a penny. A properly adjusted laser welder can weld the connectors without even warming delicate, heat-sensitive parts only a few thousandths of an inch away.
And the super-beam of the laser can be used for ultra-fine machining. Western Electric, for example, wanted to enclose precision resistors in glass tubes, then adjust the resistance after the tube was sealed. So they aim at the resistor right through the glass, burning away small bits until the resistance is the proper value.
By any count, the most widespread use of lasers so far in industry has been as a replacement for the surveyor’s transit telescope. The drilling of the 8,000-foot Azotea Tunnel under a mountain near Chana, New Mexico, was guided by a laser beam, as was the tunnel under San Francisco Bay for the new subway. Once a laser beam is set up, its pencil-thin beam serves as a simple reference to guide drilling crews. Many pipeline companies now use lasers to guide the digging of the trench.
The University of Maryland aligned the 16-ton steel slabs of its new cyclotron to 1/1,000 of an inch with a laser. The Stanford University two-mile-long linear accelerator was laid out the same way.
The laser is doing more sophisticated jobs, too. For example, an ordinary gyroscope uses a rapidly spinning ball to keep track of its direction. A new gyro built by Honeywell does the same thing with laser light beams.
The laser gyro is built in the shape of a triangle, with mirrors at each corner. Two beams revolve around this triangular racecourse, one in each direction. Detectors in the tube constantly measure the frequencies of the two beams.
If the ship or plane in which the gyro is mounted turns, the instrument turns with it. The frequency detector in the laser tube is moving in the same direction one of the light beams is rotating; it’s moving opposite to the direction of the other. The well known Doppler effect (which makes an approaching locomotive whistle appear to be higher in pitch, a receding one lower) makes one beam appear to get higher in frequency, the other lower. By measuring the apparent Doppler shifts, the machine can compute the amount and duration of the turn.
Such gyros, while not now quite so accurate as the old spinning-ball type, have several important advantages. First, they’re totally immune to acceleration or g forces, which can upset gyros in a plane or spaceship. They’re also inherently simpler, cheaper, and more reliable.
Lasers can be used to measure distances with incredible accuracy. An instrument called a geodimeter or geodolite, depending upon who makes it, measures distance to within about one inch in 15 miles. Many geodimeter lines stretch across California’s active earthquake zones. By measuring them regularly, geophysicists have noticed several sharp earth movements immediately preceding earthquakes. With the help of a laser distance-measuring system, they hope to work out a system of earthquake forecasting.
The most accurate measuring job in history got underway last July 20, when Neil Armstrong and Buzz Aldrin placed on the surface of the moon a device called the laser reflector. Since then, astronomers on earth have been bouncing laser beams off the reflector, getting ever more-accurate measurements of the earth-moon distance. Within a few months, they hope to know the distance accurate to an astonishing six inches. Before, we knew it to 600 feet.
With the new super-accurate measurements, scientists hope to learn a number of important things. Among them:
â€¢ how the mass inside the moon is distributed. This in turn may help answer questions about how it came into being.
â€¢ The rate at which the continents on earth are drifting apart.
â€¢ Changes in location of the earth’s North Pole. This could help explain why we have earthquakes.
â€¢ Whether gravity is constant, or slowly weakening as some physicists suspect.
Holography. The coherent light of the laser has made possible an entirely new branch of science called holography, a kind of lensless photography. Holograms are made by illuminating a subject with a beam of laser light, and at the same time exposing the film to a direct beam from the same laser. There is no lens involved, and the film doesn’t record a picture as we know it, but a coded version of the light rays â€”scientists call them interference patterns.
The final product looks like a smudged, greyish transparency. But illuminate it with laser light, and a picture suddenly seems to leap into midair. It doesn’t look like a picture. It looks like the real, three-dimensional object. Move your head and you can see around itâ€”see some part you couldn’t see beforeâ€”just as you can when you move your head to get a new view of a real-life object.
With its super realism, holography can do a lot of jobs that regular photography can’t. For example, Uni-Royal was recently looking for a way to find defects in tires without cutting them open. A new technique developed by GC Optronics of Detroit proved to be just the thing. The whole contraption sits on a platform the size of a pool table. A collection of lenses splits the light from a laser and shines it both on the tire and directly on a piece of photographic film. As technicians pump air in the tire, they expose the film twice at brief intervals, making a deliberate double exposure. When the film is developed, hidden defects are obvious. Where the tire has inflated evenly, there is no change. But any place there is a ply separation, linear overlap, or other defect, a series of concentric circles, interference rings, show up clearly on the picture.
Other researchers have used holography to make out-of-focus pictures clearer, to identify fingerprints automatically, to make extra-sharp photomicrographs, and even let you play -back prerecorded color tapes over your TV set (see PS December, 1969). Two New Orleans engineers, R. E. Butler and D. H. Walsh, working with doctors at Tulane Medical School, have invented a way to filter out unwanted parts of an X ray with holography. For example, doctors could get a better look at the lungs if the ribs weren’t in the way. So the engineers devised a holographic filter to get rid of the ribs. Now, small variations in lungs that could not be seen previously stand out clearly.
Television. Another promising area: big-screen color TV. The current color TV tube has about reached its limit. And that three-color dot system doesn’t produce the sharpest pictures. A much better TV system could be built using three laser beamsâ€”red, blue, and greenâ€”projected on a screen. The screen could be any sizeâ€”it could cover a living-room wall or the end of a theatre.
At least two such systems have been built. General Telephone and Electronics has demonstrated a four-foot-wide TV picture. And now, at Expo 70 in Japan, Hitachi has on display a system with a picture 9 by 12 feet. People who have seen it say the picture is more brilliant and lifelike than the one we see on regular color TV sets.
Ultimately, such wall-to-wall TV may be practical in our homes. But right now, there’s a problem. Most lasers are highly inefficient. The big-screen laser display in Japan uses three lasers, each putting out about 7 watts of power. But it takes 30 kilowatts to run the equipmentâ€”too much for use in the home.
You may be even more surprised by a whole new class of military applications for the laser. For example, microscopic lasers (like the tiny injection laser I saw at RCA) are mounted in the nose of bombs being used now in Viet Nam. They do the job that used to be done by the radar proximity fuse, but they’re smaller and lighter, and can’t be jammed.
Other lasers of the same type are mounted in arrays of hundreds or thousands (the numbers are classified) to light up the countryside at night with invisible infrared rays. Yet other types of lasers are guiding bombs to their targets, mapping the countryside from the air, “serving as rangefinders for tanks and helicopters.
In fact, almost unknown to the general public, lasers have already become operational battlefield weapons. If they’re not yet as common as bullets, at least they’re recognized as one of the mainstays of modern military technology.
Technical details of virtually all military equipment are, of course, secret. But some of the startling facts are now coming out. For example, the most dramatic new technique in use is the laser-guided bombing system, developed under the Air Force’s Pave-way program. Here’s how it works:
An FAC (forward air controller) flies over a target and spots it through a special sight. As he keeps it in his viewer, an invisible infrared laser beam stabs down from the plane and hits the target.
Then another nearby plane drops its bomb. The bomb has an infrared homing device in its nose, and moveable guide surfaces in place of the regular fins. It homes in on the reflected infrared beam, eliminating the normal errors that make for missed target: pilot error, bomb-release mechanisms that don’t work quite right, ballistic uncertainties such as wind.
The system is spectacularly successful. Normally, a bomb will land within about a 300-foot circle centered on the target. That’s its circular error probability (CEP). The laser bomb’s CEP is 10 feetâ€”a direct hit nearly every time. Dr. John S. Foster, the Defense Department’s research chief, told a congressional committee that laser bombing accuracy is at least ten times better than the old way. Now the Air Force is working on hardware to aim rockets, missiles, machine guns, and cannon with the laser system.
That’s just the beginning. Perkin Elmer Corporation has built a night-vision camera now operating in the RC-4C reconnaissance aircraft. As the plane flies across enemy terrain, a laser beam sweeps back and forth across the ground beneath it. A camera aboard builds up a picture of the laser-illuminated ground, just as the flying spot on a TV camera constructs a picture. Hughes Aircraft, Xerox, RCA, Texas Instruments, and other companies are working on similar devices.
Hughes has built laser rangefinders for the Army’s M-60A1E2 tank; RCA developed one for the MBT-70 tank. The Lockheed AH-56 helicopter also has a laser range-finder system.
The accuracy of such devices is awesome; Spectra Physics gave a demonstration a couple of years ago by flying one of its laser distance-measuring devices 1,000 feet over a Philadelphia football stadium. A regular radar altimeter would have shown the slope of the seats. The laser showed each row of seats, the spaces between, and the slight depression that thousands of shoes had worked in the track at ground level.
Other fantastic laser devices may be in the offing. According to the highly reliable journal, Aviation Week, a laser weapon developed by the Defense Department’s Advanced Research Projects Agency recently succeeded in shooting down a drone target aircraft.
The possibility of a laser heat weapon (the heat ray) was suggested 10 years ago. But there just weren’t any lasers powerful enough. About four years ago, however, an entirely new device called the carbon dioxide laser was invented. And last April, Avco Research Laboratory announced a CO2 laser with a power of up to 60 kilowattsâ€”thousands of times larger than any continuous-beam laser of just a short time back.
Reports now are that the Defense Department has developed secret devices than can crank out up to hundreds of kilowatts.
Meanwhile, the number of proposed and actual laser uses continues to grow almost daily. Among recent ones.
â€¢ a burglar alarm system with miniature injection lasers built into an ordinary looking electric wall outlet.
â€¢ a holographic device to set Chinese type automatically.
â€¢ a short-range radar to spot pebbles and other small obstructions on railroad tracks where ultra-fast trains will run.
â€¢ a short-range laser radar to spot obstructions behind your car. It could keep you from backing over a tool, a toyâ€”or a child.
â€¢ a laser milk sterilizer.
â€¢ a laser-equipped cane for the blind that sends out beams of invisible light to detect holes or obstructions on the ground, at waist level, and at eye level.
â€¢ a laser device to verify credit cards.
â€¢ an automatic reader to identify freight cars as they roll by.
â€¢ a typewriter eraser that vaporizes dark ink on a page with one zap, and does it so fast that the white paper beneath is not even scorched.
That last one was invented and patented by Dr. Arthur Schawlow, one of the originators of the laser concept. He says he’s going to market it eventually.
Dr. Schawlow also predicts that the laser will ultimately become so cheap and common that it will be used for scores of everyday tasks around the factory, office, and home. One day, he says, we’ll use laser for everything from lighting the gas range to peeling potatoes.