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No other scientific discovery of the 20th century has been demonstrated with so manyexciting applications as laser acronym for (Light Amplification by Stimulated Emissionof Radiation). The basic concepts of laser were first given by an American scientist,Charles Hard Townes and two Soviet scientists, Alexander Mikhailovich Prokhorov andNikolai Gennediyevich Basov who shared the coveted Nobel Prize (1964). However, THMaiman of the Hughes Research Laboratory, California, was the first scientist whoexperimentally demonstrated laser by flashing light through a ruby crystal, in 1960.Laser is a powerful source of light having extraordinary properties which are not found inthe normal light sources like tungsten lamps, mercury lamps, etc. The unique property oflaser is that its light waves travel very long distances with e very little divergence. In caseof a conventional e source of light, the light is emitted in a jumble of e separate wavesthat cancel each other at random (Fig. 1.1a) and hence can travel very short distancesonly. An analogy can be made with a situation where a large number of pebbles arethrown It into a pool at the same time. Each pebble generates a wave of its own. Since thepebbles are thrown at random, the waves generated by all the pebbles cancel each otherand as a result they travel a very short distance only. On the other hand, if the pebbles arethrown into a pool one by one at the same place and also at constant intervals of time, thewaves thus generated strengthen each other and travel long distances. In this case, thewaves are said to travel coherently. In laser, the light waves are exactly in step with eachother and thus have a fixed phase relationship (Fig. 1.1b).It is this coherency that makes all the difference to make the laser light so narrow, sopowerful and so easy to focus on a given object. The light with such qualities is not found
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