1、Unit Ten Lasers,Passage A What is a Laser? Passage B Introduction: Super-tool Passage C Lasers,Passage A What is a Laser?In H. G. Wellss The War of the Worlds, published in 1898, extraterrestrial aliens wreak destruction on our planet with their “heat ray”, a beam of energy so hot, so powerful, that
2、 it destroys anything it touches. “Suddenly there was a flash of light,” wrote Wells. “It was sweeping round swiftly and steadily, this flaming death, this invisible, inevitable sword of heat.” Wellss heat ray, which inspired generations of science-fiction writers to imagine ray guns and death rays,
3、 was a chillingly accurate premonition of plans to use the high-energy infrared laser as a weapon.,When real lasers finally arrivedin 1960writers and moviemakers immediately leaped upon their destructive power and substituted the word “laser” for ray gun. A laser was one of the leading pieces of mac
4、hinery in the James Bond techno-spy thriller Goldfinger in the early 1960s. As you may recall, Bond (Sean Connery played the role at the time) was tied down to a metal table by the villain Goldfinger, his legs spread apart, while a laser made its way directly toward his genitals. The lasers bright,
5、red, thick beam easily cut a swath through the table. It obviously had the power to tear him asunder, lengthwise.,This is, alas, the most popular image of the laser. A ray gun. A death ray. And indeed, some lasers do cut through metal and some can be used as weapons. But this image of the laser is a
6、 reflection more of the need for drama in works of fiction than of the lasers potential usefulness in our society. Most laser beams cant cut or burn and are at best faint pencil lines in the air, light scattered by dust. The nice sharp pictures of laser beams in this book are taken by projecting the
7、 beams through clouds of smoke, which scatter their light enough to allow them to be seen and photographed.,So how should you think of the laser? Think of it simply as a tool. One that uses light instead of mechanical energy. And a tool that allows its user to control the form and amount of energy d
8、irected at a particular place. The laser can cut through a two-inch-thick sheet of steel or detect a single atom. It can perform a task as dramatic as igniting a thermonuclear fusion reaction or as seemingly mundane as drilling a hole in a baby-bottle nipple.,A laser is a device that produces a very
9、 special kind of light. You can think of it as a super flashlight. But the beam that comes out of a laser differs from the light that comes out of a flashlight in four basic ways: Laser light is intense. Yet only a few lasers are powerful. Thats not the contradiction you might think. Intensity is a
10、measure of power per unit area, and even a laser that emits only a few milli-watts can produce a lot of intensity in a beam thats only a millimeter in diameter.1 In fact, it can produce an intensity equal to that of sunlight. An ordinary light bulb emits more light than a small laser like this, but
11、that light spreads out all over the room. Some lasers can produce many thousands of watts continuously; others can produce trillions of watts in a pulse only a billionth of a second long., Laser beams are narrow and will not spread out like ordinary light beams. This quality is called directionality
12、. You know that even the most powerful flashlight beam will not travel far. Aim one at the sky, and its beam seems to disappear quickly. The beam begins to spread out as soon as it leaves the flashlight, eventually dispersing so much as to be useless. On the other hand, beams from lasers with only a
13、 few watts of power were bounced off the moon, and the light was still bright enough to be seen back on the earth. One of the first laser beams shot at the moonin 1962spread out only two and a half miles on the lunar surface. Not bad when you consider that it had traveled a quarter of a million mile
14、s!, Laser light is coherent. This means that all the light waves coming out of a laser are lined up with each other. An ordinary light source, such as a light bulb, generates light waves that start at different times and head in different directions. Its like throwing a handful of pebbles into a lak
15、e. You cause some tiny splashes and a few ripples, but thats about all. But if you take the same pebbles and throw them one by one, at exactly the right rate, at the same spot, you can generate a more sizeable wave in the water. This is what a laser does, and this special property is useful in a var
16、iety of ways. Put another way, a light bulb or a flashlight is like a shotgun; a laser is like a machine gun., Lasers produce light of only one color. Or, to say it in a more technical way, the light is monochromatic. Ordinary light combines all the colors of visible light (i.e., the spectrum). Mixe
17、d together, they come out white. Laser beams have been produced in every color of the rainbow (red is the most common laser color), as well as in many kinds of invisible light, but each laser can emit one color and one color only. There are such things as tunable lasers, which can be adjusted to pro
18、duce several different colors, but even they can emit only one color at a time. A few lasers can emit several monochromatic wavelengths at oncebut not a continuous spectrum containing all the colors of visible light as a light bulb does. And then there are many lasers that project invisible light, s
19、uch as infrared and ultraviolet light.,KEY WORDS extraterrestrial 地球外的，地球大气圈外的 inevitable 不可避免的，不可逃避的，必定的 premonition 预感，预兆 asunder 分开地(的)，分离地(的) alas 唉，哎呀 drama 剧本，戏剧，戏剧的演出 ignite 点火，点燃，使兴奋 thermonuclear 热核的 fusion 熔解，熔化 coherent 紧凑的，表达清楚的，粘附的，相干的 pebble 卵石，水晶透镜 monochromatic 单色的，单色光的，黑白的,NOTES1 In
20、tensity is a measure of power per unit area, and even a laser that emits only a few milli-watts can produce a lot of intensity in a beam thats only a millimeter in diameter. 强度是每单位面积上能量的度量，即使一个仅产生几毫瓦能量的激光器也能产生一个直径只有1毫米的高强度光束。 后半句的主句为a lasercan produce a lot of intensity in a beam。,EXERCISES 1. Fill
21、in the blanks.(1) When real lasers finally arrivedin 1960writers and moviemakers immediately their destructive power and substituted the word “laser” for ray gun.(2) The lasers bright, red, thick beam easily cut a swath the table.(3) One that uses light mechanical energy.(4) But the beam that a lase
22、r differs from the light that comes out of a flashlight in four basic ways.(5) Intensity is a measure of power per unit area, and even a laser that emits only a few milli-watts can produce intensity in a beam thats only a millimeter .,(6) The beam begins to spread out it leaves the flashlight, event
23、ually dispersingto be useless.(7) A few lasers can emit several wavelengths at oncebut not a continuous spectrum containing all the colors of visible light as a light bulb does.,2. True/False.(1) A laser was one of the leading pieces of machinery in the James Bond techno-spy thriller Goldfinger in t
24、he early 1970s.( )(2) This is, alas, the most popular image of the laser. A ray gun. A death ray. And indeed, some lasers do cut through metal and some can be used as weapons.( )(3) Most laser beams can cut or burn and are at best faint pencil lines in the air, light scattered by dust.( )(4) It cant
25、 perform a task as dramatic as igniting a thermonuclear fusion reaction or as seemingly mundane as drilling a hole in a baby-bottle nipple.( ),(5) An ordinary light bulb emits more light than a small laser like this, but that light spreads out all over the room.( )(6) An ordinary light source, such
26、as a light bulb, generates light waves that start at different times and head in different directions.( )(7) There are such things as tunable lasers, which can be adjusted to produce several different colors, but even they can emit only one color at a time.( ),Passage B Introduction: Super-tool What
27、 Are Lasers Good For?The range of uses for the laser is striking, going far beyond the original ideas of the scientists who developed the first models(though they dont like to admit this), as well as vastly beyond the visions of the early science-fiction writers, who more often than not were simply
28、looking for a futuristic weapon(though they too are not about to admit their lack of vision).1The wide variety of lasers is also striking. At one end of the scale, there are lasers made from tiny semiconductor chips similar to those used in electronic circuits, no larger than grains of salt (a kind
29、of laser that Gordon Gould, one of the pioneers of the field, says surprised him when it was introduced). At the other end, there are the building-size laser weapons that the military is testing, quite different from the hand-held ray guns of science-fiction writers.,Our purpose in this book is not
30、only to explain lasers but to tell you about all the ways in which theyre now usedand will be used in the near futureand about how lasers will therefore affect our lives. The tasks that lasers perform range from the mundane to the esoteric, but they usually have a common element: they are difficult
31、or impossible with any other tool.2 Lasers are relatively expensive tools and are usually brought in to do a job only because they can deliver the required type and amount of energy to the desired spot. Charles H. Townes, one of the inventors of the laser and a Nobel prize-winner, told us recently t
32、hat he believes the laser “is going to touch on a very great number of areas. The laser will do almost anything. But it costs. That is the only limitation.”,The $50,000 Scalper and Television FibersA typical surgical laser, for example, costs from $30,000 to $50,000 and up, or about a thousand times
33、 more than a good conventional scalpel. And to be honest, for many operations a scalpel may be better than a laser. But if you have a detached retina, a condition that could lead to blindness, you may be happy that these expensive scalpels exist. A laser can do what a knife cant: weld the retina bac
34、k to the eyeball. No incision is required for this delicate surgery, which can be performed right in the doctors office. The laser beam shines through the lens of the patients eye and is focused on the retina, producing a small lesion that helps hold it to the eyeball. Exotic as this sounds, a simil
35、ar laser treatment has become a standard way of curing blindness caused by diabetes. (Charles Townes finds this application of the laser amazing. He admitted to us recently that the adaptation of the laser for medical uses took him by surprise, especially the detached retina procedure.),Laser medici
36、ne probably hasnt touched you personally(youd know if it had), but laser communication has undoubtedly served you already. If you watched the 1980 Winter Olympics from Lake Placid, New York, or any recent football game from Tampa Bay (Florida) Stadium on television, you saw signals that were transmi
37、tted part of the way to your home by laser. Lasers carry telephone signals in dozens of places around the country. In both cases, light from the lasers is carried through hair-thin fibers of glassfiber opticsa technology that could ultimately bring a multitude of new communication services into your
38、 home.,Death Rays, Drills, Nuclear FusionLasers are already commonplace items among our military, but probably not in the way you think. Their main function in the business of war is that of range finder and target designator, not ray gun. Lasers measure the distances to targets or pinpoint them wit
39、h a “bulls-eye,” helping either guns or missiles to home in on the enemy. And yes, in an offshoot of H. G. Wellss idea, the U.S. military is also spending about $300 million a year trying to build lasers able to destroy targets ranging from helicopters to ballistic missiles and satellites. The Sovie
40、t Union has a comparable program and is believed to have already used a laser to temporarily blind the sensitive electronic “eyes” of a U.S. spy satellite.,In factories around the world, lasers are now used routinely to drill holes in diamonds, label automotive parts, and weld battery cases for hear
41、t pacemakers. Laser quality-control “inspectors” sit ever-vigilant on assembly lines, making sure that the sizes of parts do not deviate from an acceptable range.One of the hopes for ending our energy problems is thermounuclear fusion, the process by which our sun generates its energy. One way of cr
42、eating fusion here on earth is to heat and compress pellets containing hydrogen to the temperatures and pressures needed to fuse the nuclei of the hydrogen atoms together, creating tiny hydrogen bombs and thus generating incredible power.3 What can compress these pellets? Lasers, of course.,Three-di
43、mensional Images and Super ReadersLasers are what make holograms possiblethose three-dimensional images that seem to float before you, suspended in space. But holography has many seemingly mundane applications as well, from testing the quality of aircraft tires to measuring heat flow to aiding in th
44、e design of such things as hair dryers.Lasers have made new art and new entertainment forms possible, even beyond holography. Laser light shows, the best known of which is Laserium, have been seen by millions of people around the world. A laser is also at the heart of one type of videodisk player, t
45、hat new device that plays back movies and television programs prerecorded on phonograph like disks.,Lasers can read. Those cryptic bar codes on food packages in supermarkets are read by scanning them with a laser beam. The pattern of reflected light is decoded to tell a computer in the back of the s
46、tore what the label says. This not only tabulates the price on the cash register but automatically registers in the computers inventory memory. Lasers also read special typewriter faces, so that manuscripts can be typeset automatically, without human aid.And laser can write. Its simple for a compute
47、r to control a laser, making it write on film, special paper, or the drum of a copying machine, for later transfer to paper. Laser expose printing plates for newspapers and print statements for insurance companies and mutual funds.,KEY WORDS scalpel 轻便小刀，解剖刀 detached 分离的，分开的，孤立的 retina 视网膜 diabetes
48、糖尿病 multitude 许多，大批，大量 helicopter 直升飞机 ballistic 弹道的，射击的，冲击的 vigilant 警戒的，警惕的 nucleus (pl. nuclei) 中心，核心 hologram 全息照相，全息图 dimension 范围，方向，维，元 cryptic 隐义的，秘密的 elaborate 精心制作的，细心完成的，周密安排的,NOTES1 The range of uses for the laser is striking, going far beyond the original ideas of the scientists who dev
49、eloped the first models (though they dont like to admit this), as well as vastly beyond the visions of the early science-fiction writers, who more often than not were simply looking for a futuristic weapon (though they too are not about to admit their lack of vision). 激光的用途极其广泛，令人瞩目，远远超出了设计第一代模型的科学家
50、们的想像(尽管他们不愿承认)，也极大地超出了早期科幻小说家的想像，这些小说家只是单纯地寻找一种未来武器(尽管他们也不愿承认自己缺乏想像力)。,2 The tasks that lasers perform range from the mundane to the esoteric, but they usually have a common element: they are difficult impossible with any other tool. 激光器能完成从平凡到神秘的多种任务，但这些任务通常都有一个共同点：它们很难或不可能由其他工具来完成。 句中的两个they均指the
51、tasks。3 One way of creating fusion here on earth is to heat and compress pellets containing hydrogen to the temperatures and pressures needed to fuse the nuclei of the hydrogen atoms together, creating tiny hydrogen bombs and thus generating incredible power. 在地球上实现熔合的途径是对含有氢气的气团加温加压，以达到使氢原子熔合的温度和压力，产生小型氢弹，因而出现难以想像的巨大能量。,
