Check your understanding

Exercise 1. Answer the following questions.

1. What are the major properties of laser radiation?

2. In what way is a laser used in practice?

3. What is the working element of a ruby laser?

4. When was the first semiconductor laser invented?

5. What elements does it consist of?

6. What do two parallel mirrors provide?

7. At what temperatures do these lasers operate?

8. In what way is the p-n junction made?

9. Under what conditions does the laser emit light?

10. What semiconductors are used in the injection lasers?

11. What are the advantages of a semiconductor laser?

Exercise 2. Define what is true and what is false.

1. Laser light can travel a large distance in outer space with little reduction in signal strength.

2. The gallium arsenide semiconductor laser was invented in 1962.

3. The lasers usually operate at 77⁰C or lower.

4. When the intense electric current about 10000 amperes per square centimeter is applied to the device, it emits coherent or incoherent light.

5. The mirrors on either end of the active region provide the optical feedback.

Exercise 3. Finish the sentences with the suitable parts.

1. In practice a laser is used as…

1. ... an amplifier of current.

2. ... a source of radiation.

3. ... a frequency converter.

2. This intensity of the laser radiation...

1. ... is equal to that of the spontaneous radiation.

2. ... is smaller than that of the spontaneous radiation.

3. ... exceeds that of the spontaneous radiation.

3. A resonant cavity is necessary …

   1. … to produce photon emission.

   2. … to produce coherent radiation.

   3. … to produce diffusion electron.

3. In semiconductor laser light is emitted …

   1. … from a layer of the p-type GaAs.

   2. … from a layer of the n-type GaAs.

   3. … from the junction between the two layers.

3. Two parallel mirrors in the laser provide …

   1. …a resonant cavity.

   2. …a p-n junction.

   3. …optical pumping.