Unit 10 Lasers,Passage A What is a Laser? Passage B Introduction: Super-tool Passage C Lasers,When real lasers finally arrivedin 1960writers and moviemakers immediately leaped upon their destructive power and substituted the word “laser” for ray gun. But this image of the laser is a reflection more of the need for drama in works of fiction than of the lasers potential usefulness in our society. The nice sharp pictures of laser beams in this book are taken by projecting the beams through clouds of smoke, which scatter their light enough to allow them to be seen and photographed.,Think of it simply as a tool. One that uses light instead of mechanical energy. Intensity 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.1 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 miles!,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. 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., 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). Mixed 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 produce several different colors, but even they can emit only one color at a time.2 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, such as infrared and ultraviolet light.,NOTES 1 Intensity 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。,2 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. 激光束可以是彩虹中的每一种颜色(红色是最常见的激光颜色), 还可以是许多种看不见的光, 但每个激光器能且只能发出一种颜色的光。 ,Exercises 1. Fill 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 laser 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, eventually dispersing to 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 the 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 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 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 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 looking for a futuristic weapon(though they too are not about to admit their lack of