The Connection Between Atoms and Lasers

A laser is a device that controls the way in which energised atoms release photons. There are many different types of laser available; all the different types of laser rely on the same basic elements. In all types of laser there is a lasing medium, which is pumped to get the electrons within the atoms to a higher-energy orbital i.e. to get the atoms excited. Typically, very intense flashes of light or an electrical discharge pump the lasing medium and create a large number of excited-state atoms. This creates a high degree of population inversion (the number of excited state atoms versus me number of atoms at ground-state energy level). At any stage the excited state atoms can release some of the energy and return to a lower-energy orbital. The energy released, which comes in the form of photons, has a very specific wavelength that is dependant on the level of energy or excitation of the electron when the photon is released. Two identical atoms with electrons in identical states will release photons with identical wavelengths. This forms the basis for laser light.

Laser light has the following properties:

• Laser light is monochromatic. It contains one specific wavelength of light, which as described earlier is determined by the amount of energy released when the electron drops to a lower-energy orbital.

• Laser light is coherent. Each photon moves in step with the other (i.e. all photons have wave fronts that move in unison).

• Laser light is highly directional (i.e. a laser beam is very tight and concentrated.

Any photon that has been released by an atom, (which therefore has a wavelength, phase and energy level dependant on the difference between the excited atom state and the ground-state energy level) should encounter another atom that has another electron in the same excited state, stimulated emission can occur. The first photon can stimulate or induce atomic emission so that the emitted photon vibrates with me same frequency and direction.

Understanding a printed text

TASK 6

Translate the text and answer the questions.

Lasers in Communication

Fiber optic cables are a major mode of communication partly because multiple signals can be sent with high quality and low loss by light propagating along the fibers. The light signals can be modulated with the information to be sent by either light emitting diodes or lasers. The lasers have significant advantages because they are more nearly monochromatic and this allows the pulse shape to be maintained better over long distances. If a better pulse shape can be maintained, then the communication can be sent at higher rates without overlap of the pulses. Telephone fiber drivers may be solid state lasers consuming power of only half a milliwatt. Yet they can sent 50 million pulses per second into an attached telephone fiber and encode over 600 telephone conversations.

1. What is the text about?

2. Why are fiber optic cables becoming a major mode of communication?

3. What lasers may be telephone fiber drives?

4. How many telephone conversations can be encoded per second?

TASK 7

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Laser cutters are credited with keeping the U.S. garment industry competitive in the world market. The programmed cutter can cut dozens to hundreds of thicknesses of cloth, and can cut every piece of the garment in a single run. The usefulness of the laser for such operations comes from the fact that the beam is highly collimated and can be further focused to a microscopic dot of extremely high energy density for cutting.

TASK 8

Read the text given below and answer in what abstract your can you find the information about:

1. holography;

2. b)using of laser beams in building construction;

3. computing the distance to the Moon;

4. medical uses of lasers.