No other scientific discovery of the 20th century has been demonstrated with so many
exciting applications as laser acronym for (Light Amplification by Stimulated Emission
of Radiation). The basic concepts of laser were first given by an American scientist,
Charles Hard Townes and two Soviet scientists, Alexander Mikhailovich Prokhorov and
Nikolai Gennediyevich Basov who shared the coveted Nobel Prize (1964). However, TH
Maiman of the Hughes Research Laboratory, California, was the first scientist who
experimentally 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 in
the normal light sources like tungsten lamps, mercury lamps, etc. The unique property of
laser is that its light waves travel very long distances with e very little divergence. In case
of a conventional e source of light, the light is emitted in a jumble of e separate waves
that cancel each other at random (Fig. 1.1a) and hence can travel very short distances
only. An analogy can be made with a situation where a large number of pebbles are
thrown It into a pool at the same time. Each pebble generates a wave of its own. Since the
pebbles are thrown at random, the waves generated by all the pebbles cancel each other
and as a result they travel a very short distance only. On the other hand, if the pebbles are
thrown into a pool one by one at the same place and also at constant intervals of time, the
waves thus generated strengthen each other and travel long distances. In this case, the
waves are said to travel coherently. In laser, the light waves are exactly in step with each
other 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, so
powerful and so easy to focus on a given object. The light with such qualities is not found