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5. Answer the following questions:

1. What is a laser? 2. What is the gain medium of a laser? 3. Can particles of electrons interact with light? 4. Is the output laser beam emitted through the mirror? 5. Does laser consist of a gain medium inside a highly reflective optical cavity? 6.When is the energy supplied? 7. Is photon emitted in the same direction as the light that is passing by? 8. Does laser produce light by itself?

6. Match the first part (1-5) of the sentence with the second part (a-e) :

1. The emitted laser light ...

2. A beam produced by a thermal or other incoherent light source ...

3. Pumping can interact with light by …

4. Particles have …

5. Emission ...

6. The gain medium ...

7. Stimulated emission is …

8. An optical amplifier is …

9. A light beam or beam of light is ….

a) … a device that amplifies an optical signal directly, without the need to first convert it to an electrical signal.

b) … the process by which an atomic electron (or an excited molecular state) interacting with an electromagnetic wave of a certain frequency.

c) … an instantaneous amplitude and phase which vary randomly with respect to time and position.

d) … a narrow projection of light energy radiating from a source into a beam.

e) … is notable for its high degree of spatial and temporal coherence.

e) … is the process of supplying the energy required for the amplification is called.

f) … is a material with properties that allow it to amplify light by stimulated emission.

g) … can be spontaneous or stimulated.

h) … either absorbing or emitting photons.

7. Read the supplementary text, translate and entitle it:

Many scientific, military, medical and commercial laser applications have been developed since the invention of the laser in the 1958. The coherency, high monochromaticity, and ability to reach extremely high powers are all properties which allow for these specialized applications. In science, lasers are used in many ways, including: spectroscopy, atmospheric remote sensing, holographic techniques . Laser based LIght Detection And Ranging (LIDAR) technology has application in geology, seismology, remote sensing and atmospheric physics. Lasers have been used aboard spacecraft such as in the Cassini-Huygens mission. In astronomy, lasers have been used to create artificial laser guide stars, used as reference objects for adaptive optics telescopes.

Most types of laser are an inherently pure source of light; they emit near-monochromatic light with a very well defined range of wavelengths. By careful design of the laser components, the purity of the laser light (measured as the "linewidth") can be improved more than the purity of any other light source. This makes the laser a very useful source for spectroscopy.

8. Render the text: Laser

UNIT 8

Pre-text exercises:

1. Choose the right word: Say, tell, speak, talk

1. Don't … him about our plans. 2. I waited for an answer, but she didn't … a word.

3. He … us that he was going to buy a new car. 4. Do you … English? 5. Mike, we need to … . 6. To … you the truth, I don't remember anything. 7. Did the director … at the conference? 8. Do you know how to … good-bye in Arabic?