МГТУ им. Н.Э. Баумана, 2020 г.
РУБЕЖНЫЙ КОНТРОЛЬ ПО ДИСЦИПЛИНЕ
ИНОСТРАННЫЙ ЯЗЫК (АНГЛИЙСКИЙ) РЛ2 МОДУЛЬ 16
ВАРИАНТ № 1
I. Grammar Complete the sentences 1-10, using the correct forms of the words, putting the prepositions where required.
1. The military has long been one of … users of the laser technology. (big)
2. When Theodore Maiman developed the first practical laser, few people … how important these machines … eventually …. (to realize, to become)
3. Depending on the type of laser, different gain media … can be used. (a solid, liquid or gas substance)
4. The experiment … on for a long time. I wonder what the result will be. (to go)
5. Are you going to read the report? No, I … I know what it says. (mustn't, shouldn't, needn't, can't)
6. He had a strange habit of … in other people's business. (to interfere)
7. In 1957 Gordon Gould, sketched in his lab notebook an idea for how a visible light version of the maser … work, coining the word "laser" that we've used ever since. (may, was to, could, has to)
8. Nobody knew what … next. (to happen)
9. When the laser was invented, few people realized what a wonderful device it …. (to be)
10. He didn’t remember where he … before the accident. (to be)
II. Read the text and answer the questions
You often read in books that "laser" stands for Light Amplification by Stimulated Emission of Radiation. It’s actually a very clear explanation of how lasers make their super-powerful beams of light. The radiation lasers make has nothing to do with dangerous radioactivity. Lasers make electromagnetic radiation, just like ordinary light, radio waves, X rays, and infrared. Although it's still produced by atoms, they make ("emit") it in a totally different way, when electrons jump up and down inside them. We can think of electrons in atoms sitting on energy levels, which are a bit like rungs on a ladder. Normally, electrons sit at the lowest possible level, which is called the atom's ground state. If you fire in just the right amount of energy, you can shift an electron up a level, onto the next rung of the "ladder." That's called absorption and, in its new state, we say the atom is excited—but it's also unstable. It very quickly returns to the ground state by giving off the energy it absorbed as a photon (a particle of light). We call this process spontaneous emission of radiation: the atom is giving off light (emitting radiation) all by itself (spontaneously).
Normally, a typical bunch of atoms would have more electrons in their ground states than their excited states, which is one reason why atoms don't spontaneously give off light. But what if we excited those atoms—pumped them full of energy—so their electrons were in excited states. In that case, the "population" of excited electrons would be bigger than the "population" in their ground states, so there would be plenty of electrons ready and willing to make photons of light. We call this situation a population inversion, because the usual state of affairs in the atoms is swapped around (inverted). Now suppose also that we could maintain our atoms in this state for a little while so they didn't automatically jump back down to their ground state (a temporarily excited condition known as a meta-stable state).. If we fired a photon with just the right energy through our bunch of atoms, we'd cause one of the excited electrons to jump back down to its ground state, giving off both the photon we fired in and the photon produced by the electron's change of state. Because we're stimulating atoms to get radiation out of them, this process is called stimulated emission. We get two photons out after putting one photon in, effectively doubling our light and amplifying it (increasing it). These two photons can stimulate other atoms to give off more photons, so, pretty soon, we get a cascade of photons—a chain reaction—throwing out a brilliant beam of pure, coherent laser light. What we've done here is amplify light using stimulated emission of radiation—and that's how a laser gets its name.
1. What kind of radiation does a laser produce?
2. What is absorption in a laser?
3. Which atoms are called excited?
4. How the population inversion is created?
5. What is the difference between spontaneous emission and stimulated emission?
МГТУ им. Н.Э. Баумана, 2020 г.
РУБЕЖНЫЙ КОНТРОЛЬ ПО ДИСЦИПЛИНЕ
ИНОСТРАННЫЙ ЯЗЫК (АНГЛИЙСКИЙ) РЛ2 МОДУЛЬ 16
ВАРИАНТ № 2
I. Grammar and vocabulary Complete the sentences 1-10, using the correct forms of the words, putting the prepositions where required.
1. The situation was bad but it … worse. (could, should be, could have been, would have been)
2. The device … for too long, probably it will soon fail. (to work)
3. The processed target detection information … be displayed to an operator. (must, can, may, should)
4. The researcher knew that it was he who … a mistake and he … for the failure of the project. (to make, to be responsible)
5. The big advantage of liquid dye lasers is that they can be used to produce a … band of light frequencies than solid-state and gas lasers. (broad)
6. It suggested that he must … all of the materials beforehand. (to read)
7. His experience in the field of material science can … upon. (to rely)
8. Come in and have a seat. We … the design of a new device for half an hour yet. (to discuss)
9. Since the temperature of the gas in laser can affect the discharge conditions, questions of cooling … be addressed. (could, have to, must, may)
10. She showed no sign of … when she learned the results of the experiment. (to surprise)
II. Read the text and answer the questions
Lasers produce light but they are more than just powerful flashlights. The difference between ordinary light and laser light is like the difference between ripples in your bathtub and huge waves on the sea. The difference is not only in power, there are other more significant differences. Where a flashlight produces "white" light (a mixture of all different colors, made by light waves of all different frequencies), a laser makes what's called monochromatic light (of a single, very precise frequency and color—often bright red or green or an invisible "color" such as infrared or ultraviolet). Where a flashlight beam spreads out through a lens into a short and fairly fuzzy cone, a laser shoots a much tighter, narrower beam over a much longer distance (we say it's highly collimated). Where the light waves in a flashlight beam are all jumbled up (with the crests of some beams mixed with the troughs of others), the waves in laser light are exactly in step: the crest of every wave is lined up with the crest of every other wave. We say laser light is coherent. A flashlight beam can be considered as a crowd of commuters, pushing and shoving, jostling their way down the platform of a railroad station; by comparison, a laser beam is like a parade of soldiers all marching precisely in step. Why do they make a so powerful single color and a coherent beam? It refers down to the idea that energy can only exist in fixed packets, each of which is called a quantum. It's a bit like money. You can only have money in multiples of the most basic unit of your currency, which might be a cent, penny, rupee, or whatever. You can't have a tenth of a cent or a twentieth of a rupee, but you can have 10 cents or 20 rupees. The same is true of energy, and it's particularly noticeable inside atoms. Like the rungs on a ladder, the energy levels in atoms are in fixed places, with gaps in between them. You can't put your foot anywhere on a ladder, only on the rungs; and in exactly the same way, you can only move electrons in atoms between the fixed energy levels. To make an electron jump from a lower to a higher level, you have to feed in a precise amount (quantum) of energy, equal to the difference between the two energy levels. When electrons flip back down from their excited to their ground state, they give out the same, precise amount of energy, which takes the form of a photon of light of a particular color. Stimulated emission in lasers makes electrons produce a cascade of identical photons—identical in energy, frequency, wavelength—and that's why laser light is monochromatic. The photons produced are equivalent to waves of light whose crests and troughs line up (in other words, they are "in phase")—and that's what makes laser light coherent.
1. What is monochromatic light?
2. Why is laser Light coherent?
3. Can energy exist inside atoms in any amount?
3. How much energy it is necessary to feed to an electron to transfer it to a higher level?
4. Why is laser light monochromatic?