Text A. The laser today and tomorrow

The laser has become a multipurpose tool. It has caused a real revo­lution in technology.

Atoms emit rays of different length, which prevents the forming of an intense beam of light. The laser forces its atoms to emit rays having the same length and travelling in the same direction. The result is a nar­row, extremely intense beam of light that spreads out very little and is therefore able to travel very great distances.

The most common laser is the helium-neon laser in the laser tube, containing 10 per cent helium gas and 90 per cent neon gas. At the end of the tube there is a mirror, and at the other end there is a partial mir­ror. The electrons get energy from a power supply and become "ex­cited", giving off energy as light. This light is reflected by the mirror at one end of the tube. It can only escape through the partial mirror at the other end of the tube.

The first laser was built in 1960. Since then scientists have devel­oped several types of the laser which make use of luminescent crystals, luminescent glass, a mixture of various gases and finally semiconductors.

Having been developed at Lebedev Institute of Physics in 1962, semiconductor quantum generators occupy a special place among the optical generators. While the size of the ruby crystal laser comes to tens of centimetres and that of the gas generator is about a metre long, the semiconductor laser is a few tens of a millimetre long, the density of its radiation being hundreds of thousands of times greater than that of the best ruby laser.

But the most interesting thing about the semiconductor laser is that it is able to transform electrical energy directly into light wave energy. With an efficiency approaching 100 per cent as compared to a maximum of about 1 per cent of other types, the semiconductor laser opens up new possibilities of producing extremely economical sources of light.

But it is in the field of communication that the laser will find its most extensive application in future. Scientists foresee the day when a single la­ser beam will be employed to carry simultaneously millions of telephone conversations or a thousand of television programmes. It will serve for fast communications across continents, under the sea, between the Earth and spaceships and between men travelling in space

The potential importance of these applications continues to stimulate new development in the laser field

Vocabulary:

the laser — слово лазер состоит из начальных букв фразы, описывающей функцию прибора: Light Amplification by Stimulated Emission of Radiation — усиление света в результате вынужденного излучения

partial mirror — полупрозрачное стекло

power supply — источник питания

approach — приближаться; достигать

beam — луч

carry — передавать

compare — сравнивать

density — плотность

emit — излучать

employ — использовать

extensive — обширный

foresee (foresaw; foreseen) — предвидеть

intense — интенсивный

mirror — зеркало

narrow — узкий

prevent — препятствовать

single — один, единственный

spread (spread) — распространяться

travel v — двигаться

Exercise 1. General understanding: