Laser

“ But with even less exotic devices than lasers, the road from the laboratory to the marketplace may often be long and hard. Price, efficiency, reliability, convenience—these are all factors that must be considered. It soon became clear that with something as new as the laser, much improvement was necessary before it could be used in science and medicine, and even more before it could be used in industry. ”

“ But it is also possible to focus laser light as no light has ever been focused before. At close range a laser beam can be focused down to a circle just a few wavelengths across, concentrating its energy and making it possible to drill holes only 0.0002 inch in diameter. ”

“ Sunlight focused onto the side of the laser (see Figure 32) provides the pumping power, enabling the device to put out 1 watt of continuous infrared radiation, enough for special space applications. Descendents of this device could produce visible light if this is deemed desirable.
Another approach, using chemical lasers, is even more intriguing and may have greater consequences. Chemical lasers will derive their energy from their internal chemistry rather than from the outside. A mixture of two chemicals may be all that is needed to initiate laser action aboard a spacecraft or satellite. ”

“ In this booklet we shall learn what there is about the laser that gives it so much promise. We shall investigate what it is, how it works, and the different kinds of lasers there are. We begin by discussing some of the more familiar kinds of radiation, such as radio and microwaves, light and X rays.
5 THE ELECTROMAGNETIC SPECTRUM
Some 85% of what man learns comes to him through his vision in response to the medium of light. Yet, ironically, it wasn’t until the end of the 17th century that he first began to get an inkling of what light really is. ”

“ When two laser beams touch, they produce an interference pattern of light and dark ripples that can be recorded on a photographic plate. And if one of the beams, instead of coming directly from the laser, is reflected first off an object such as a human face, the resulting pattern will be very complex indeed, but it can still be recorded. ”

“ An input of radio waves of the proper frequency did the job very nicely.
But most significant of all, Javan’s gas laser provided the first continuous output. This is commonly referred to as CW (continuous wave) operation. The distinction between pulsed and CW operation is like the difference between baking one loaf of bread at a time and putting the ingredients in one end of a baking machine and having a continuous loaf emerge at the other.
When a non-expert thinks of a laser, he is apt to think of power—blinding flashes of energy—as illustrated in Figure 26. ”

“ Pumping light (wavy arrows in a) raises most of the atoms to the excited state, creating the required population inversion.
Figure 18 Sequence of operations in a solid crystal laser. (a) Pumping light raises many atoms to excited state. (b) Lasing begins when a photon is spontaneously emitted along the axis of the crystal. This stimulates other atoms in its path to emit. (c) The resulting wave is reflected back and forth many times between the ends of the crystal and builds in intensity until finally it flashes out of the partially silvered end. ”

“ However, it is often asserted that machining the laser end mirrors to high accuracy may be a major roadblock to automated manufacture of lasing devices. Nazemetz (personal communication, 1980) has pointed out that a laser is accurate enough to surface a rough-hewn mirror to the accuracy required for its own construction. In a pinch, concave mirrors could be hewn from solid metal or basalt blanks simply by sweeping the laser beam radially across the disks, applying higher power nearer the center so more material volatizes there, thus creating a perfect spherical or parabolic surface gradient. ”

“ A laser printer. Typically, it works a bit like some copying machines, with your computer controlling the printed image rather than a document you put in front of a mirror. This wasn’t the choice for me; laser printers at the time went for several thousand dollars up. By now, however, the price may be much lower. Political fund-raisers love the nice quality that lasers can add to slick letters saying how badly they need your money. ”

“ The narrow beam of the laser offers one more fascinating possibility, especially in the case of satellites relatively near earth. The light of a laser might actually be used to beam energy to a receiver, either for immediate use or 51 storage. It would then become possible to “refuel” satellites at will, giving them much greater capabilities.
If available laser power is great enough, laser beams might even be used to push satellites back into their proper orbits when they begin to wander off course, as they almost invariably do after a while. ”

“ The earth shook and a great cloud of dust arose from the site, momentarily hiding the laser units. A light morning breeze drifted the dust downstream in a minute.
Ten huge holes gaped in the river bed underneath the laser beam heads mounted on adjustable cranes out and away from their power units.
"Fire," came the order again. This time there was nothing but the trembling of the earth as the beams cut a molten path through rock, clay, sand and boulders.
"Measure," the engineer ordered. A radar gauge bounced a beam off the bottom of one of the holes. ”

“ Precision machining of liquid- and air-tight valves, laser mirror surfaces, and various other small intricate parts will demand the closest scrutiny of the rate at which energy is delivered to the workpiece. Lasers may also be used for super-accurate ranging and sizing measurements, which require an ultralow power capability as well as sophisticated optics, timing, and data processing systems. Automation of the LMF Laser Machining System will require close computer/mechanical control to perform each of the seven basic machining steps described earlier in section 5F.5. ”

“ The crucial difference between the sun’s light or any ordinary kind of light and laser light lies in the extent to which the emission of energy can be controlled. In the production of ordinary light the atoms, as we know, emit spontaneously, or in an uncontrolled fashion. But if the atoms could be forced to take in the proper amount of energy, store it, and release it when we wanted them to, we would have stimulated, rather than spontaneous, emission. ”

“ Scientists are experimenting with a new kind of “lens”, one that uses variations in the density of gases to focus and guide the beam automatically. Since there are no surfaces in the path of the light beam, and since the gas is transparent and free of turbulence, the laser beam is not appreciably weakened or scattered as it travels through the pipe. ”

“ Since the beam of laser energy is narrow, it would be possible for the radiation to miss the earth altogether and be lost entirely unless the laser were pointed at the receiver with extreme precision. Aiming a gun at a target 50 yards away is one thing; aiming a laser from an unmanned spacecraft 100 million miles away is quite another. ”

“ You are familiar with a watt and have an idea of its magnitude: think, for example, of a 15-watt or a 150-watt bulb. A watt is a unit of power; it is the rate at which (electrical) work is being done.
Figure 26 High power is demonstrated as a laser beam blasts through metal chain.
44
The joule is a unit of energy and can be thought of as the total capacity to do work. One joule is equivalent to 1 watt-second, or 1 watt applied for 1 second. But it can also mean a 10-watt burst of laser light lasting 0.1 second, or a billion watts lasting a billionth of a second. ”

“ A possible solution is the use of “light pipes”, similar to the wave guides already in use for certain microwave applications over short distances. But as often happens, new developments create new needs; how, for example, can we get the laser beam to stay centered in the pipe and follow curves? ”

“ But such mirrors must be made and adjusted to exceptionally close tolerances to allow useful output, and must operate in a vacuum for best effect. Multilayer dielectric mirrors with a reflectivity of 99.9999 percent were developed. The invention of laser light sources and fiber-optics has enabled the production of small, light, and dependable ring laser gyros. Mirror-based devices continue to be used in physics research. ”

“ IF YOU NEED LASER FLAVOR, TAKE SOME NUTS, CRUSH THEM; THEY WILL IMPART TO YOUR DISH AN ADMIRABLE FLAVOR. REPLACE THE USED NUTS WITH A LIKE NUMBER OF FRESH ONES [3]
[1] List. and G.-V. uncia—ounce. Making an ounce of laser go a long way. Tor. nucea; Tac. nucia. Lister, fond of hair-splitting, is irreconcilably opposed to Tor., and berates Caspar Barthius for defending Tor. List. ”

“ With proper auxiliary equipment, bursts of several billion watts have been achieved; but the burst lasts only about 100 millionths of a second. For certain uses, that’s just what is wanted: a highly concentrated burst of energy that does its work without giving the material being “shot” a chance to heat up and spread the energy, perhaps damaging adjacent areas.
Figure 27 Active substance for a modern liquid laser is made in an uncomplicated 10-minute procedure. Bluish powder of the rare earth, neodymium, is dissolved in a solution of selenium oxychloride and sealed in a glass tube. ”

“ High-frequency resistance and induction welding can also join a wide variety of materials, and with high efficiency. Table 4.29 compares key characteristics of laser and electron-beam processes with those of two less-promising alternatives for space and lunar applications. It is apparent that both E-beam and laser techniques are competitive in most categories whether on Earth or in space. Equipment cost of the E-beam should be much lower in a vacuum environment, since the major expense in terrestrial applications is for the maintenance of proper vacuum. ”

“ A laser system called Doppler LIDAR (light detecting and ranging) reflects energy from "aerosols" (minute particles) instead of raindrops. This system can avoid picking up ground clutter (moving cars, etc.) ”

“ Television programs must compete for space on cross-country networks with telephone, telegraph, and transmission of data. The increasing use of computers in science, business, and industry will strain our facilities still further. Communication satellites will help, but they will not give us the whole answer; and much development work remains to be done on satellites.
Figure 2 Precision control of a machine tool by laser light.
Why the interest in the laser for communications? In a recent experiment all seven of the New York TV channels were transmitted over a single laser beam. ”

“ Laser beam machining is "especially adaptable and principally used for relatively small materials processing applications such as cutting, trimming, scribing, piercing, drilling, or other delicate material removal operations similar to milling or shaping" (Yankee, 1979) .
Dunning (unpublished Summer Study document, 1980) has suggested a variety of space and lunar applications for laser machining, including flash trimming of cast basalt parts; engraving bar codes on parts to enable quick and accurate recognition by robot vision systems; drilling holes in workpieces an inch thick or less ”

“ The purpose of describing the above nonlaser welding and machining systems is to suggest that laser machining should be equally automatable because the laser may be viewed as another modality for delivering heat or cutting action to a workpiece. Any nonlaser automated welding/machining technology in principle may be modified to accept a laser as its active machining element. ”

“ R&D required - Further developments in electron-beam and laser technologies are likely to be highly fruitful. Laser flashlamp lifetimes must be greatly increased. Qualitative Tukey Ratio - The Ratio is somewhat poor for solid-state lasers using present-day technologies, though the components are not too massive and so could be lifted from Earth with only modest penalty. ”

“ Laser cutting speeds typically are as much as 30 times faster than friction sawing (Yankee, 1979) . Cutting accuracy is about 0.01 mm/cm under closely controlled conditions. All metals - including high-strength, exotic, and refractory alloys such as Inconel and titanium, as well as aluminum, stainless steel, and brass - and nonmetals such as diamond, ceramics, and plastics may be vaporized by laser beams. Hence, parts of these materials may be easily machined. Burr-free laser holes may be drilled as small as 10-100 μm. ”

“ It had two dials on it with signs of calibration, and a button that was probably intended to activate it. "If it is a laser, and if these dials move the power from low to high, who knows which end is which?"
"Take it into the power plant and aim it at the floor. An instrument that small can't have too much power and won't hurt a half mile of solid iron. See what happens," suggested Mark. ”

“ Mike turned back to the laser milling machine. "Now can we take the focusing lens off of this, and rig something to give me a focus at about 4.5 miles? Or would it need focusing at all? Shooting at that distance?"
"Depends on what you shoot, Mike. The unfocused beam can make a black surface very hot very quick. But from a mirror surface, it would just bounce, unless it's carefully focused."
"It ought to take care of the plastic at least, then."
"Go right through it. You gonna laser Hot Rod?"
"No. Just the anchor tubes that hold the mirror ”